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Eclipse Forms: Rich UI for Rich Client Applications

摘要: Spice up your rich client with rich user experience using Eclipse Forms. Written as a thin layer on top of SWT, Eclipse Forms allow you to achieve the Web look in your desktop applications without using the embedded browser. This allows you to retain full control of the widgets in the UI and to maintain portability across all operating systems Eclipse already runs on. This article will take you from baby steps to advanced topics of the rich user interface experience of Eclipse Forms. By Dejan Glozic, IBM Canada Ltd.

The History (as we see it)

One of the fundamental features of the Eclipse platform is that applications built on top of it look, feel and smell like genuine native applications. Thanks to SWT, menus, windows, trees, tables, buttons and other widgets all feel 'right' no matter what OS or windowing system you are on. Being one of the first members of the Eclipse team, I remember the days when I could get hours of joy by playing with our prototype Eclipse code. Menus are real. Tool bars are real. Combos, text, button, check boxes, radios are all real. There is not a drawn widget in sight, all are native widgets.

For a long time, if your plug-ins contributed Eclipse user interface artifacts, they would generally fall into the following categories:

Editors
Views
Wizards
Dialogs

There are clear presentation rules for artifacts in these categories. We are used to seeing trees and tables in views, documents in editors and grids of simple widgets like buttons and text fields in wizards and dialogs. These rules are easy to follow and live by as long as your application is similar in principle to Eclipse SDK.

The RCP (Rich Client Platform) concept in Eclipse 3.x represents a fundamental broadening of the platform scope. It brought as a corollary an effective explosion of the problem domains. You can now build Rich client applications on top of Eclipse that have little in common with IDEs. While generic workbench parts like views and editors continue to work well, the widgets that are populating these parts in IDEs (trees, tables, text editors, etc...) may not be the best solution for this class of applications. Available since Eclipse 3.0, Eclipse Forms are designed to offer appealing alternatives.

Ironically, we developed Eclipse Forms as a solution for a concrete problem in the Eclipse SDK long before RCP existed as a concept. Developers of the PDE (Plug-in Development Environment) working on the plug-in manifest editor did not feel happy with following a Java editor paradigm of offering a color-coded, context-assisted text editor for the plugin.xml file. There is nothing wrong with Java editor in Eclipse by itself - in fact, it is very powerful and ideally suited for the task. However, it was designed for editing Java source files. In plug-in manifests, XML was used as a format to describe data at a higher level of abstraction. Editing XML by hand, even with color-coding and context assist/code completion was not perceived as the correct level of abstraction for the majority of users. In a plug-in manifest, the syntax itself is not important (yet another thing to learn). It is the data and what it represents that is important.

A good example of different ways of looking at markup is HTML authoring tools. At the source code level, all we can see are nested elements with the associated attributes. Although we see the syntax, it is hard to visualize what it really represents. A WYSIWYG view of the document can reveal a table, colors, some texts that span tables, images, etc. Working with HTML files at this level of abstraction is vastly more productive because syntax and markup are hidden in the background (which is the reason why I am typing this article on a WYSIWYG HTML authoring tool instead of hacking HTML tags).

It is easy to understand what WYSIWYG concept means for HTML documents. Since the HTML tags represent instructions for the web browser on how to compose a document from text, presentation attributes, hyperlinks and images, WYSIWYG in this context means editing the document in its final form -- as close as possible to the way it will appear in the browser. It was harder to figure out what the alternative presentation would mean for the plug-in manifest editor. Ultimately, the team made the following decisions:

Represent each section of the manifest in the way most suitable for its nature. For example, vital information like plug-in name, provider etc. can be easily edited in a text field. Hierarchical structure of extensions maps nicely into the tree widget etc.
Show sections of the manifest on separate editor pages, regardless of their physical order in the source
Pages of the editor would keep a document feel and would be able to host a mix of widgets, hyperlinks, images and text, and offer scroll bars when content is too large for the page size.

Figure 1: The Plug-in manifest editor as it first appeared in Eclipse SDK 1.0. It offered a mixture SWT widgets, hyperlinks and images that could scroll when there is not enough space (as you would expect in a web browser). Note how all the widgets have the 'flat' look that was selected for less clutter and better fit in the document context.

The third point effectively spelled the birth of a plug-in that now goes by the name of Eclipse Forms. Soon after release 1.0, other developers wanted to replicate the rich user interface that appeared in PDE multi-page editors. It was finally made available as a plug-in with public APIs in Eclipse 3.0.

In the following text, we will show you what Eclipse Forms are (and what they are not) and how to use them to create rich UI with little effort.

Eclipse Forms Mission

Now that we know how Eclipse Forms came into being, it is useful to describe their mission before going into details:

Let's look at the mission statement in more detail:

Point cannot be underestimated. When building interfaces in Eclipse Forms, you are using SWT. There is no Eclipse Forms button, or Eclipse Forms tree widget as an alternative to SWT widget. Instead, you are using Eclipse Forms support to tweak subtly the existing widget set to achieve a richer user experience.

Eclipse Forms make these rich user interfaces possible with the following elements:

A concept of a 'form' that is suitable for inclusion in content areas such as views and editors
A toolkit to manage colors, hyperlink groups and other aspects of a form, and serve as a factory for many SWT controls
A new layout manager that lays out controls in a manner similar to an HTML table layout algorithm
A set of custom controls designed to fit in the form (hyperlink, image hyperlink, scrollable composite, section)
A multi-page editor where most or all of the pages are forms (e.g. PDE manifest editors)

Although nothing in the design of Eclipse Forms prevents you from creating a form in a dialog, most of the usage scenarios have been focused on using forms in views and editors, rather than dialog and wizards. It is a matter of consistency -- having only a few form-based dialogs or wizards would look very strange when all other dialogs are 'normal'. Nevertheless, it is an interesting area to explore in the future.

Baby steps

It is very easy to start using Eclipse Forms in your user interfaces. You can start by adding a dependency on org.eclipse.ui.forms plug-in. We will create an Eclipse view that hosts a form and gradually fill in the content. Note that the plug-in with all the source code used in this article is available as a zip archive.

Hello, Eclipse Forms

We will start playing by adding an empty form to a view:

As you can see from this code snippet, it does not take much to create a form. We start by creating an instance of a toolkit ( ). We use the toolkit to create a scrolled form using the provided composite as a parent. We set the title of the form. We also make sure to transfer focus to the form when needed and dispose the toolkit when the view is disposed.

When we register the view using the class shown above and launch the second Eclipse instance, the view should look like this:

Figure 2: A simple empty form in a view. Making the view narrower will cause the form title to wrap. Once there is no more space to fit the entire form, scroll bars will appear.

Note that we have used scrolled form because we placed it in a view that can be resized. In the more complex situations where a form needs to be a child in a layout, a non-scrolled version is available. In this case, we would have called FormToolkit.createForm() instead and let the outmost parent worry about scrolling the overall content.

Adding some content

Now that we have the form view running, we can start adding some content to it. Eclipse forms have a body and we should create all the content there:

The body of the form is the usable space below the form title. Since this space is a SWT Composite, it can serve as a parent for other widgets. In the code above, we set the layout on the body, then create a hyperlink. The hyperlink is one of the few custom widgets that Eclipse Forms provide. The widget allows us to add a hyperlink listener so that we can be notified when the user clicks on the link.

The updated view should look like this:

Figure 3: A simple form with a hyperlink

Note how hyperlink has a focus rectangle painted around it. Upon view activation, focus is transferred to the form, which passes it to the first control capable of accepting focus -- our link in this case. With the keyboard focus in the link, simply pressing the 'Enter' key would activate the link.

Hyperlink Groups

Form toolkit has a hyperlink group object. Each created hyperlink is added to this group object. Hyperlink groups serve several roles. They define colors -- for normal, hover and active states -- for all links in the group. They change colors of the managed links based on their state. They change underline style of the managed links based on their state. They manage cursors and show busy cursor before link listeners process the link activation, and revert it after.

You can change the default settings of the hyperlink group by getting the object from the toolkit with getHyperlinkGroup().

Creating common controls

One of the design goals of Eclipse Forms was to allow the creation of common SWT controls in the editor/view content space. Since form body is a normal composite, you can use any layout and control you want inside it. However, remember that 'raw' SWT controls come with a widget background. We will now create some controls using their constructors:

layout.numColumns = 2; GridData gd = new GridData(); gd.horizontalSpan = 2; link.setLayoutData(gd); Label label = new Label(form.getBody(), SWT.NULL); label.setText("Text field label:"); Text text = new Text(form.getBody(), SWT.BORDER); text.setLayoutData(new GridData(GridData.FILL_HORIZONTAL)); Button button = new Button(form.getBody(), SWT.CHECK); button.setText("An example of a checkbox in a form"); gd = new GridData(); gd.horizontalSpan = 2; button.setLayoutData(gd);

We are now using two columns and creating a label, a text field and a checkbox. The result is below:

Figure 4: A form with SWT controls created directly using their constructors

What is wrong with this picture? The background of controls we created directly matches the system dialog background, not the form background. In addition, the text field looks fine because the screen capture was taken on Windows XP. On other windowing systems, it would look out of place due to the addition of a 3D border. To fix this problem, we will create these controls using the toolkit's factory methods instead:

Label label = toolkit.createLabel(form.getBody(), "Text field label:"); Text text = toolkit.createText(form.getBody(), ""); text.setLayoutData(new GridData(GridData.FILL_HORIZONTAL)); Button button = toolkit.createButton(form.getBody(), "A checkbox in a form", SWT.CHECK); gd = new GridData(); gd.horizontalSpan = 2; button.setLayoutData(gd);

The view will now look better:

Figure 5: A form with SWT controls created using the form toolkit as a factory

Factory methods provided by the form toolkit are there for your convenience. The toolkit is not all-inclusive --even for the SWT widget set-- and definitely not for the custom controls that you may have. A utility method FormToolkit.adapt(Control control, boolean trackFocus, boolean trackKeyboard) should be used to adapt an existing SWT control to fit into the form. Most of the factory methods call adapt themselves.

Achieving the 'flat' look

One of the recognizable attributes of Eclipse Forms used in PDE editors was the elegant 'flat' look of the controls. All the controls used there were without 3D borders that look fine in dialogs but less appealing in editors or views. This support is built into the FormToolkit class. However, on some platform it comes at a price of some custom rendering. For example, look at this screen capture from PDE editor (version 2.1):

Figure 6: The flat look of Eclipse Forms circa Eclipse 2.1

Controls like tables, text entries, combo box etc. are rendered with a flat one-pixel border. These borders do not come from the controls themselves (SWT.BORDER style is not used). Instead -- if instructed -- the toolkit will add itself as a paint listener to each control's parent, and draw borders around controls during paint events. To make this happen, you need to call the toolkit method paintBordersFor(parent) for each composite where you created controls like text, tree, table etc. Note that one call per parent is enough: there is no need to make a call for each control of this type.

The Form toolkit knows which controls require a custom border. However, you may create a new one that also needs a border that is not on the list. You can give a hint to the toolkit by adding the following code:

As you can see from the picture above, 'structural' controls like trees and tables have a border style different from text areas and you can choose which one to render for your control. Note that this is not needed for controls created using toolkit's factory methods.

Since Eclipse 3.0 and on Windows XP, no border rendering is done when the file javaw.exe.manifest file is present in the Java virtual machine bin folder (I took all the screen shots in this article on Windows XP). The presence of this file -- you can download one from the SWT home page -- instructs the toolkit to use XP skins for native widgets. With XP skins, controls like text, table and tree are already flat and there is no need to adjust the look. For your code to be portable, you should always call paintBordersFor(Composite), and let the toolkit choose what to do depending on the windowing system.

Custom layouts

Eclipse Forms offer two new layouts in addition to the base SWT layouts. These layouts extend the SWT Layout base class and can be used on any SWT composite, but are typically used in conjunction with Eclipse Forms.

TableWrapLayout

Now that we know how to populate the form, let's throw it a curve. We will change the hyperlink text to be much longer:

link.setText("This is an example of a form that is much longer "+ "and will need to wrap.");

Let's see the result on screen:

Figure 7: A form laid out using GridLayout

What happened? Remember that we are using GridLayout. When it asked the link control to compute its size, it gave it the size needed to render the text in one long line. Although we instructed the control to wrap, it did not matter because GridLayout requires that a control return its size in isolation. The link itself -- as well as other SWT controls like Label -- is capable of computing the height given its width if you pass the width instead of SWT.DEFAULT in computeSize, but GridLayout is not passing the width as an argument.

What we need is a different layout algorithm that works more like HTML tables. We want the content to try to fit in the provided client area, and grow vertically to compensate. Eclipse Forms provide an alternative layout for just such a purpose called TableWrapLayout. There are many similarities between GridLayout and TableWrapLayout. Both organize parent's children in grids. Both have layout data that instructs the layout how to treat each control. Both can accept hints on which control should grab excess space etc.

However, they fundamentally differ in the approach to the layout. TableWrapLayout starts with columns. It computes minimal, preferred and maximum widths of each column and uses this information to assign excess space. It also tries to be fair when dividing space across columns so that there is no excess wrapping of some controls.

It is possible to mix GridLayout and TableWrapLayout but the branch of widgets tree where GridLayout is used is the one where wrapping stops. This is quite acceptable if you do not want it to wrap, typically if the composite contains controls that cannot wrap anyway, like text, buttons, trees etc... However, you should have an un-broken path from the form body to each text control that needs to wrap.

Let's rework our example to use TableWrapLayout (with changes highlighted):

public void createPartControl(Composite parent) { toolkit = new FormToolkit(parent.getDisplay()); form = toolkit.createForm(parent); form.setText("Hello, Eclipse Forms"); TableWrapLayout layout = new TableWrapLayout(); form.getBody().setLayout(layout); Hyperlink link = toolkit.createHyperlink(form.getBody(),"Click here.", SWT.WRAP); link.addHyperlinkListener(new HyperlinkAdapter() { public void linkActivated(HyperlinkEvent e) { System.out.println("Link activated!"); } }); link.setText("This is an example of a form that is much longer and will need to wrap."); layout.numColumns = 2; TableWrapData td = new TableWrapData(); td.colspan = 2; link.setLayoutData(td); Label label = toolkit.createLabel(form.getBody(), "Text field label:"); Text text = toolkit.createText(form.getBody(), ""); td = new TableWrapData(TableWrapData.FILL_GRAB); text.setLayoutData(td); Button button = toolkit.createButton(form.getBody(), "A checkbox in a form", SWT.CHECK); td = new TableWrapData(); td.colspan = 2; button.setLayoutData(td); }

We used the same concepts that for GridData. Some of the variables have different names (for example, colspan and rowspan, align and valign are taken from HTML TABLE attributes), but you are doing the same thing -- creating a grid with two columns where link and button span two columns. Since margins are the same as in GridLayout, the result will look similar except the link will now wrap:

Figure 8: A form laid out using TableWrapLayout

One of the main differences between TableWrapLayout and GridLayout is that with the former you should stop thinking about the vertical dimension. In GridLayout, you would typically let the 'rigid' controls assume their natural positions and sizes and let 'flexible' controls (text, tree and table) grab horizontal and/or vertical excess space. In contrast, TableWrapLayout works top-down and when it places all the controls, its work is complete. The concept of grabbing excess space still exists in the horizontal dimension (as shown above). However, vertically you can only choose to FILL the cell in case it is taller than the control, or pick TOP, MIDDLE or BOTTOM vertical alignment.

You may notice one thing that may seem contradictory to the previous claim: TableWrapData still has grabVertical variable. However, the variable is here for a distinct purpose: when a fixed height control spans multiple rows, its height will create a local condition where vertical dimension is known, and controls in the spanned cells need to divide the extra space between them.

In order to have good results with TableWrapLayout, ensure that controls that can wrap have the appropriate style bit (SWT.WRAP). Composite custom controls provided by Eclipse Forms are wrap-enabled out of the box. This is achieved by using internal layouts that implement ILayoutExtension interface:

TableWrapLayout implements this interface itself, which allows it to handle cases where composites with this layout are children of the composite that is laid out. The additional two methods allow it to compute the two extreme cases - the absolute minimum width and the maximum width if all the controls are spread as wide as possible. The difference between the two allows the algorithm to distribute extra space fairly between columns to minimize excess wrapping.

Let's take a closer look at space distribution. We will comment the code we wrote so far in the view and replace it with the following:

layout.numColumns = 3; Label label; TableWrapData td; label = toolkit.createLabel(form.getBody(), "Some text to put in the first column", SWT.WRAP); label = toolkit.createLabel(form.getBody(), "Some text to put in the second column and make it a bit "+ "longer so that we can see what happens with column "+ distribution. This text must be the longest so that it can "+ "get more space allocated to the columns it belongs to.", SWT.WRAP); td = new TableWrapData(); td.colspan = 2; label.setLayoutData(td); label = toolkit.createLabel(form.getBody(), "This text will span two rows and should not grow the column.", SWT.WRAP); td = new TableWrapData(); td.rowspan = 2; label.setLayoutData(td); label = toolkit.createLabel(form.getBody(), "This text goes into column 2 and consumes only one cell", SWT.WRAP); label.setLayoutData(new TableWrapData(TableWrapData.FILL_GRAB)); label = toolkit.createLabel(form.getBody(), "This text goes into column 3 and consumes only one cell too", SWT.WRAP); label.setLayoutData(new TableWrapData(TableWrapData.FILL)); label = toolkit.createLabel(form.getBody(), "This text goes into column 2 and consumes only one cell", SWT.WRAP); label.setLayoutData(new TableWrapData(TableWrapData.FILL_GRAB)); label = toolkit.createLabel(form.getBody(), "This text goes into column 3 and consumes only one cell too", SWT.WRAP); label.setLayoutData(new TableWrapData(TableWrapData.FILL)); form.getBody().setBackground(form.getBody().getDisplay(). getSystemColor(SWT.COLOR_WIDGET_BACKGROUND));

This code creates a number of wrapping labels with text of variable length. Some labels span columns, some span rows. To make the test easier, we will set the form background to widget background so that cells will be easy to spot. When we run the example, we will get the following:

Figure 9: Excess space distribution in TableWrapLayout

The key in space distribution is that the difference between control minimum and maximum width is compared. The greater the difference, the greater allocation of excess width will be for the column. Excess width is any width greater than the width needed to fit all the controls with their minimum widths taken into account. Notice how column 3 is slightly wider than column 2 because text in column 2 is somewhat longer. The overall goal is to avoid excessive empty space in cells. If you want to read more about the theory behind this layout algorithm, go to W3C recommendations for HTML table auto-layout.

ColumnLayout

Another Eclipse Forms custom layout is a variation of SWT RowLayout. If we configure RowLayout to place children vertically -- in columns-- and to make all controls have the same width within a column, we would get several columns, depending on the width of controls. However, the last column would typically not be completely filled -- depending on the number of controls. When placed in a form, we would again get all the controls in one column because RowLayout cannot do 'vertical' wrapping. If we use GridLayout instead, we would have to choose the number of columns up front and live with the choice.

There are situations in more complex forms where we want the number of columns to be adaptive. In other words, we would like the number to change depending on the width of the form -- use more when possible, drop the number down as the width decreases. We would also like to fill the form area equally like a newspaper layout, with all the columns roughly the same height. All this can be achieved with ColumnLayout.

Compared to TableWrapLayout, ColumnLayout is much simpler. Hardly any configuration is needed. The only choice you need to make is the range of columns you want to have (default is 1 to 3). The following example shows a form with a large number of sections (we will talk about sections later) using ColumnLayout. Initially, there is enough space to arrange the sections in two columns. When we make the editor narrower, the layout arranges the sections in only one column:

Figure 10: Sections arranged in columns using ColumnLayout. The layout started with two columns but dropped to one when there was not enough space to fit all the sections.

Complex controls

Eclipse Forms provide four complex custom controls that can help you build rich looking UI: expandable composite, section, image hyperlink and form text. Let's look closely at each of them.

Expandable composite

A common theme in sleek web pages is the ability to collapse a portion of the page content using a toggle control. Eclipse Forms offer such a control: ExpandableComposite.

ExpandableComposite ec = toolkit.createExpandableComposite(form.getBody(), ExpandableComposite.TREE_NODE| ExpandableComposite.CLIENT_INDENT); ec.setText("Expandable Composite title"); String ctext = "We will now create a somewhat long text so that "+ "we can use it as content for the expandable composite. "+ "Expandable composite is used to hide or show the text using the " "toggle control"; Label client = toolkit.createLabel(ec, ctext, SWT.WRAP); ec.setClient(client); td = new TableWrapData(); td.colspan = 2; ec.setLayoutData(td); ec.addExpansionListener(new ExpansionAdapter() { public void expansionStateChanged(ExpansionEvent e) { form.reflow(true); } });

The composite accepts a number of styles that control its appearance and behavior. Style TREE_NODE will create the toggle control used in a tree widget for expanding and collapsing nodes, while TWISTIE will create a triangle-style toggle. Using EXPANDED will create the control in the initial expanded state. If style COMPACT is used, control will report width in the collapsed state enough to fit in the title line only (i.e. when collapsed, it will be as compact horizontally as possible). Finally, CLIENT_INDENT will indent the client to align with the title (otherwise, client will be aligned with the toggle control).

ExpandableComposite is responsible for rendering the toggle control and the title. The client control to expand or collapse must be a direct child of the expandable composite.

We needed to add expansion listener to the control and 'reflow' the form on the state change. This is because expansion causes changes in expandable composite size, but the change will not take effect until the next time the parent is laid out (hence the need to force it). In general, every time you do something that causes the layout of the form to be invalid, you need to 'reflow' the form. 'Reflowing' the form will reposition the controls according to the new sizes and update the scroll bars.

Our view now looks like this:

Figure 11: An example of the expandable composite in the collapsed state

When you click on the '+' sign or on the title itself, composite expands to reveal the client:

Figure 12: An example of the expandable composite in the expanded state

The expandable composite uses an internal layout implementing Eclipse Forms ILayoutExtension. Therefore you can add it to a parent that uses TableWrapLayout, as we did in the example above.

Section

One of the most versatile custom controls in Eclipse Forms (and seen in all PDE editors) is Section. It extends the expandable composite and introduces the following concepts:

Separator - a separator control can be created below the title
Description - an optional description can be added below the title (and below the separator, if present)
Title bar - a title bar that encloses the section can be painted behind the title (note that separator and title bar should not be used simultaneously)

The code is similar to the expandable composite code example:

Section section = toolkit.createSection(form.getBody(), Section.DESCRIPTION|Section.TITLE_BAR| Section.TWISTIE|Section.EXPANDED); td = new TableWrapData(TableWrapData.FILL); td.colspan = 2; section.setLayoutData(td); section.addExpansionListener(new ExpansionAdapter() { public void expansionStateChanged(ExpansionEvent e) { form.reflow(true); } }); section.setText("Section title"); section.setDescription("This is the description that goes "+ below the title"); Composite sectionClient = toolkit.createComposite(section); sectionClient.setLayout(new GridLayout()); button = toolkit.createButton(sectionClient, "Radio 1", SWT.RADIO); button = toolkit.createButton(sectionClient, "Radio 2", SWT.RADIO); section.setClient(sectionClient);

This time, we used the TWISTIE toggle style, added the description and asked for the title bar to be painted. The view now looks like this:

Figure 13: An expandable section with a painted title bar and a description

Image hyperlink

Image hyperlink is a subclass of Hyperlink that adds an image before the link text. This combination is so common that it just made a lot of sense to make one control out of it and save on widgets. The control can be used as an image link only (when no text is set), or as a combination of link and image. Images for normal, hover and active (selected) state can be set.

The following is an example of a rich user experience that uses image hyperlinks:

Figure 14: A form taken from one of the Eclipse Welcome pages (this is a fallback presentation used for the cases when embedded browser creation fails)

Form text control

Using the combination of labels, hyperlinks, images and TableWrapLayout, it is possible to create?complex and powerful forms. However, there are some things that are hard to do. Consider the following example from the PDE manifest editor:

Figure 15: An example of a complex Eclipse form that mixes wrapped text, images and hyperlinks

Notice how images, hyperlinks and text snippets are mixed together. This is very hard using separate label and hyperlink widgets. To remedy the problem, Eclipse Forms plug-in provides a very rudimentary text control that can do the following:

Render plain wrapped text
Render plain text but convert any segment that starts with http:// into a hyperlink on the fly
Render text with HTML-like tags (the form used in Figure 15 is using form text widgets in this mode)

In all the modes, form text control is capable of rendering either a string or an input stream.

Rendering normal text (label mode)

FormText formText = toolkit.createFormText(form.getBody(), true); td = new TableWrapData(TableWrapData.FILL); td.colspan = 2; formText.setLayoutData(td); String text = "Here is some plain text for the text to render."; formText.setText(text, false, false);

Second argument set to false means that we will not bother to parse the tags, and the third that we will not try to expand URLs if found.

Automatic conversion of URLs into hyperlinks

Now we will add a hyperlink to the text and turn the third argument into true:

FormText formText = toolkit.createFormText(form.getBody(), true); td = new TableWrapData(TableWrapData.FILL); td.colspan = 2; formText .setLayoutData(td); String text = "Here is some plain text for the text to render; "+ this text is at http://www.eclipse.org web site."; formText .setText(text, false, true);

When we look at our view, it now looks like this:

Figure 16: Form text control with a URL automatically converted into a hyperlink

The URL has been converted into a link. The link is part of the wrapped text - we did not have to create a separate Hyperlink control and try to sandwich it between the two labels.

Since form text control can render hyperlinks, it accepts the same hyperlink listeners we used before. When created by the toolkit, the form text will use the hyperlink settings from the hyperlink group that belongs to the toolkit.

Parsing formatting markup

The most powerful use of the form text control is when formatting tags are added to the text. The expected root tag is 'form'. It can have one or more children that can either be

. Either of these can have normal text, text between or tags, images and links. Images are declared using image key"/> (no content), while links are expressed using href">text.

Some of the tags mentioned above have additional attributes. Tag can accept nowrap='true' to block the link from being wrapped into the new line. Tag
can have attribute vspace='false' (true by default) that adds additional space between paragraphs when set to 'true'. Tag

has more attributes:

style - can be "text", "bullet" and "image" (default is "bullet")

value - not used for "bullet"; if style is "text", the value will be rendered instead in place of a bullet; if style is "image", value represents a key in the image table of an image to be rendered in place of a bullet

vspace - the same as for the 'p' tag.

indent - the number of pixels to indent text

bindent - the number of pixels to indent the bullet (this number is independent from 'indent' - be careful not to overlap them)

Tags that affect appearance of the normal text are (works as expected), and . The latter allows you to change font and/or color of the text within the tag. Finally, soft line breaks can be added using
tag.

Since Eclipse 3.1, it is possible to place an SWT control that is a child of the form text in the markup. The new element 'control' accepts attribute 'href' that is a key to the Control object set using FormText.setControl(String key, Control control). Optionally, attribute "fill" can be set to true to make the control fill the entire width of the text. Form text is not responsible for creating or disposing controls, it only places them relative to the surrounding text. Similar to , vertical position of the control relative to the surrounding text can be set using the 'align' attribute.

How does all this work in practice? Let's make data text that will use all of these tags together:

StringBuffer buf = new StringBuffer(); buf.append("<form>"); buf.append("
"); buf.append("Here is some plain text for the text to render; "); buf.append("this text is at http://www.eclipse.org web site."); buf.append("
"); buf.append("
"); buf.append(""+ "This text is in header font and color."); buf.append("
"); buf.append("
This line will contain some bold and "+ "some source text. "); buf.append("We can also add an image. "); buf.append("
"); buf.append("

A default (bulleted) list item.

"); buf.append("
Another bullet list item.
"); buf.append("
A list item with text.
"); buf.append("
Another list "+ item with text
"); buf.append("
List item with "+ "an image bullet
"); buf.append("
"+ "A list item with text.
"); buf.append("
"+ "A list item with text.
"); buf.append("
leading blanks; more white \n\n new "+ "lines
\n more bb white .
"); buf.append("</form>"); FormText formText = toolkit.createFormText(form.getBody(), true); formText.setWhitespaceNormalized(true); td = new TableWrapData(TableWrapData.FILL); td.colspan = 2; formText.setLayoutData(td); formText.setImage("image", FormArticlePlugin.getDefault(). getImageRegistry().get(FormArticlePlugin.IMG_SAMPLE)); formText.setColor("header", toolkit.getColors(). getColor(FormColors.TITLE)); formText.setFont("header", JFaceResources.getHeaderFont()); formText.setFont("code", JFaceResources.getTextFont()); formText.setText(buf.toString(), true, false); formText.addHyperlinkListener(new HyperlinkAdapter() { public void linkActivated(HyperlinkEvent e) { System.out.println("Link active: "+e.getHref()); } });
One common theme that can be observed is that the widget itself is not responsible for loading images, fonts, resolving links or colors. This is not a browser and it is much better to separate concerns and simply assign images and colors managed elsewhere. Both links and images simply have 'href' attribute to reference them. For links, the value of this attribute will be provided in the hyperlink event when listeners are notified. Images need to be registered with the text control using the matching 'href' key. This way, the control does not need to worry about loading the images - it has them in the hash table and can render them immediately.

A similar approach has been used for colors and fonts. Colors are already handled by the toolkit, so you can allocate as many as you want using a unique key and RGB values by calling toolkit.getColors().createColor(String key, RGB rgb). What is left is to set all the colors referenced in the 'span' tag so that the control will be able to use them during rendering.

When the code above is executed, the view looks like this:

Figure 17: Form text rendered from the XML markup

If we expand the section and the expandable composite, and make the window narrower, the form still holds and everything wraps perfectly:

Figure 18: The sample view made taller and narrower

Appropriate usage and limitations

Although the image above is very promising, it is very important to contain excitement. A 'prime directive' of the form text control is:

It is very easy to spot limitations of the control. Tags within list items or paragraphs cannot be nested. Bold is supported, but not italic (although any font can be set and associated via the 'span' tag). Attributes for vertical alignment of text with respect to images are missing. List support is decidedly low level. There is no BIDI support.

Another important limitation to consider is performance. Form text is neither a performance nor memory hog, but it was written to be small and lean, not powerful. For that reason, it does not have sophisticated painting routines, dirty region management etc. These routines are cost-effective when the control owns the entire window and must be scalable. In contrast, form text is best suited for short snippets of tagged text that are mixed with other controls on a form. This way, the control is one of several children in the parent, allowing native dirty region management from the OS to handle repaints. The best results in Eclipse forms are achieved with a mixture that is similar to our example above.

Performance and painting of the form text widget has been improved in Eclipse 3.1 and it can now handle more content without performance degradation. For example, the new Help view is using form text widget for rendering hundreds of images and search hits. Nevertheless, the usage guidelines outline above still stand.

If you have a problem with the form text limitations, you should consider alternatives:

If you need editing capability and text styling (with different fonts and colors), use StyledText (used by styled text editors like Java editor in Eclipse)

If you only need read-only support but have complex text formatting needs, use org.eclipse.swt.browser.Browser. Embedded web browser works on most platforms and will give you full HTML support.

What this widget is for is to provide for modest text formatting in combination with TableWrapLayout and other controls in a form. The power lies in the fact that you have full access to every control - a kind of direct access that you can only achieve in a browser if you use proprietary DOM access mechanisms. In contrast, Eclipse Forms are portable - they run everywhere SWT runs.

To conclude, use the form text widget:

when the UI you want to render is not very long with many lines of text, hyperlinks and many images in complex layouts (use embedded browser for that)

when you want to mix text, hyperlinks and images with SWT controls like trees, tables and buttons.

when you want to run everywhere SWT runs

In contrast, use embedded web browser:

when the UI you want to render contains many lines of text, hyperlinks and images arranged in complex layouts

when you do not need to mix SWT controls like trees and tables with the text

when you want to use complex web technologies like animation, sound or servlets/JSPs and/or render external web pages in-place

when you want to achieve complex rendering effects like transparency (all SWT widgets are opaque)

when you only need to ship on OS and/or window system combinations where the embedded browser is fully supported

Advanced Topics

As usual in the real-world development, there is a chasm between simple, happy examples that get you started and real code shipped in products. This section covers aspects of Eclipse Forms that are employed in production Eclipse code. You do not need to use them right away, but chances are you will recognize their advantages as your plug-in grows in complexity. In the following text, we will address color and toolkit management, managed forms, master/details block and multi-page editors.

Color And Toolkit Management

When using forms in a non-trivial way, it is important to share as much as possible to conserve resources. For this reason, color management should be separated from the toolkit when there is more than one form to handle.

Of course, it is possible to create one toolkit per form, but that is too wasteful if there are many forms. Instead:

Create one toolkit for all the forms that have the same life cycle. For example, if creating a multi-page editor, create one toolkit per editor and dispose it when editor is disposed. All the pages in the editor should share this toolkit.

Create one color manager (FormColors) per plug-in. When creating the toolkit, pass the color manager to the toolkit. The toolkit will know that the colors are shared and will not dispose them.

Use platform support for fonts and if possible, use JFaceResources predefined fonts. Between default, 'banner' and 'header' fonts, you can accomplish a lot. Using many fonts is very confusing for the user, and if you do manage your own, you must ensure alternatives across platforms. The JFace fonts are guaranteed to work on all the platforms Eclipse ships on.

Dispose the color manager on plug-in shutdown (do not assume that plug-in shutdown also means platform shutdown - in Eclipse 3.x OSGi can uninstall your plug-in dynamically with the platform still running).

Use form color manager to allocate all the colors needed by the forms.

Managed forms

Managed forms are wrappers that add life cycle management and notification to form members. A managed form is not a form by itself. It has a form and accepts registration of IFormPart element. For each IFormPart, it manages events like dirty state, saving, commit, focus, selection changes etc. In order to reach to the wrapped form widget, call the 'getfForm()' method.

Not every control on the form needs to be a form part. It is better to group a number of controls and implement IFormPart interface for the group. Section is a natural group and Eclipse Form provides SectionPart implementation. It implements the interface and contains a Section instance (either created outside and passed into the constructor, or created in the part itself).

Master/Details block

'Master/Details' is a pattern used throughout the UI world. It consists of a list or a tree ('master') and a set of properties ('details') driven by the selection in the master. Eclipse Forms provide the implementation of the pattern as a useful building block with the following properties:

While 'details' part is managed by the class itself, the master part factory method is abstract and must be implemented by the subclass

Master and details parts are children of a sash form and the ratio of the form space allocated for each can be changed by moving the sash.

As usual with a sash form, master and details parts can be organized horizontally or vertically in the form.

The idea of master/details block is to create a tree or a table section that fires the selection notification via the managed form. If the details part can handle the selected object, it should switch to the page for it and display properties. When building on top of the provided master/details block, subclasses should:

Create the master part (the one that drives the details)

Contribute actions to the form tool bar (consumes upper-right portion of the form in the title area)

Register details pages, one for each distinct input that can arrive from the master part

We will show how this looks in practice using the source code that accompanies this article. It creates a table for the master part and hooks a few dummy objects of two distinct types. Two details pages are registered to handle selections of these types. Pages can contain any number of controls - they are created on demand in the provided parent. The details area scrolls separately from the master area.

This part can now be used anywhere, but in this example it was placed inside an editor. Two distinct object types were used (TypeOne and TypeTwo), and their classes were used directly as keys (other mapping between details pages and objects are possible). Details pages registered with the Details part need to implement IDetailsPage interface.

The page is first initialized with the managed form to get access to the toolkit and other objects. It is then asked to create contents in the provided parent. It should also set focus on the first control when asked, be able to refresh, commit, dispose and react to the input changes. As long as objects selected in the master part are of a compatible type, the page will stay visible and inputChanged will be called.

Let's see how all this looks in practice:

Figure 19: An example of a master/details block in horizontal orientation hosted in an editor

An instance of TypeOne object is selected in the master part. The appropriate page for the type is loaded in the details part. The page can contain any number of controls introduced elsewhere in this article. The ratio of parts on the page can be changed by scrolling the sash (visible when mouse goes over the area between the parts). Also note two actions in the upper-right corner of the form - this is the form tool bar. In this case, two radio buttons were contributed to control orientation of the part (horizontal or vertical).

If we change the orientation and select one of the TypeTwo instances, we get into this state:

Figure 20: The same block in vertical orientation and with a different element type selected

Orientation is now vertical, and a different details page is shown for the type.

It is possible to register a detail page provider instead of registering pages up front. This allows dynamic resolution of the details page for the selected object. It is particularly important for cases when different pages are needed for objects of the same type depending on their states.

Multi-page form editors

It was a long way to get to this topic, yet PDE multi-page editors were the first to spark interest in Eclipse Forms. Today, multi-page editors still represent the most common use case of the technology, even though it now starts to appear in other places.

Eclipse Forms are designed to work in a variety of settings. For this reason, the plug-in cannot make assumptions on the types of editor inputs your editor can receive. A number of concepts employed in PDE UI cannot be used here because without knowing about the editor input in more detail, it is hard to provide a set of reusable classes. Nevertheless, Eclipse Forms provide the basic support for multi-page editors, which you can build on.

You should start building an Eclipse Forms multi-page editor by extending FormEditor:

A very simple way to get started is to create pages and add them as above. Each page needs to implement FormPage and override createFormContent(IManagedForm managedForm). Since there is already a managed form in each page, you should create contents in that enclosed form and register any form part that needs to be part of the managed life cycle.

In addition to form pages, you can add one or more text editors as a raw source alternative to the GUI pages. For this, you should call addPage(IEditorPart, IEditorInput input) method in the super class.

Multi-page editor example

The source code that comes with this article contains an example of a multi-page editor suitable for inclusion in an RCP application because it does not have any dependencies on IDE plug-ins.

Once you launch another Eclipse application, customize the perspective by checking the following checkbox in the test Eclipse window:

Window>Customize Perspective...>Commands>Eclipse Forms Article

This will add a menu to the menu bar called 'Form Article Editors'. The menu contains only one action - 'Simple Form Editor'. The action will open the editor. It has the following pages:

Figure 21: A multi-page editor page with a free-flowing text

The first page contains a page with a TableWrapLayout and some sample content including a FormText widget. The page content is free-form and will wrap and flow top to bottom.

In contrast, the second page contains 'stretchy' controls -- two table viewers -- that consume all the excess space on the page. Since the controls can scroll themselves, a GridLayout is used. Several PDE editor pages follow this pattern.

Figure 22: A multi-page editor page with sections and tables.

The third page (Flow Page) was shown before in the ColumnLayout section. It demonstrates how to use this layout to adjust to the available space. Master/Details sections are also shown above.

The last page shows how to embed aCTabFolder in order to add another dimension to a form. In this particular example, the actual content is not switched -- there is only one text control -- but its content is loaded from different objects depending on the selected tab.

Figure 23: A multi-page editor page with nested tabs

Recommended practices for Eclipse Forms multi-page editors

There are many ways to write a form-based multi-page editor. It depends on the type of content you are editing and the proficiency of your users. You can approach it in two ways:

If the typical users are using the editor infrequently, if raw source is hard to edit by hand or complex, if your users are not very technical, you should make COMPLETE pages capable of editing every aspect of the content without the need to turn to the raw source. In this approach, a source editor page is there only for occasional validation, rather than for regular work. In that case, you can get away with a basic text editor. The PDE extension point schema editor falls into this group.

If your users are more technical, if they have no problem editing the file by hand but would appreciate some help from time to time, then consider providing a mixed experience -- make a good source editor with all the add-ons like incremental outline, context assist, syntax highlighting etc. Then, add complex value-added functionality in form pages for actions that are hard to achieve when editing raw source. We have learned from experience that it is very hard to convince seasoned users to switch from source editing if the value added is marginal or debatable. However, when a function is only available in GUI pages and provides value and usability, it is adopted readily.

Creating a quality multi-page editor with mixed GUI and source pages has its challenges. Accepting that users will switch pages frequently requires a good model of the underlying content. The model should be directly tied to the underlying document(s) to stay in sync when users edit the raw text directly and when they change it structurally through the forms pages. Also, do not forget indirect changes caused by other workbench actions while the editor is open.

For ideas on how to do this, see the source code of PDE editors (org.eclipse.pde.ui plug-in) from the Eclipse CVS repository.

Conclusion

The goal of this article was to introduce you to a great way to create powerful user interfaces in Eclipse 3.x. Eclipse Forms is neither a competing widget toolkit that you need to choose over SWT, nor does it make the embedded HTML browser widget obsolete. Instead, it is a carefully written extension of SWT that allows you to create surprisingly rich user interfaces in Eclipse while retaining the portability of SWT. In simple cases, it can also be a lightweight alternative to the SWT embedded browser widget. When used within its limitations, Eclipse Forms can spice up your applications and allow you to introduce a familiar Web-like metaphor.

Source Code

To run the example or view the source code for this article, go through the following steps:

Unzip formsArticle.zip into your workspace location in the file system.

Import the extracted project (org.eclipse.ui.forms.article) into your workspace using 'File>Import>Existing Project into Workspace'

Browse the source code (under 'src' directory).

When ready, launch another Eclipse using 'Run>Run As>Eclipse Application'

To browse the sample view, use 'Window>Show View>Other...>Eclipse Forms Article Examples>Eclipse Form'

To browse the multi-page editor, check the 'Window>Customize Perspective>Commands>Eclipse Forms Article' checkbox to activate the action set. After that, activate the editor from the newly added 'Form Article Editors' menu.

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