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E4/DeclarativeUI/XWT
Contents
Name of Technology
XWT Here is a presentation of our vision File:XWT.pdf
Purpose
Adopt a direct mapping XML to SWT/JFace with the support of JFace DataBinding
Contact
Committers
Yves YANG, Thomas Guiu and others
Current License
XWT is an Open Source under EPL Licnese.
Description
XWT is a markup language for declarative application programming. It is a specific solution of using XML grammar for SWT/JFace directly.
XWT simplifies UI programming. You can create visible UI elements in the declarative XML markup with a physical separation of the UI definition from the run-time logic. An XML based declarative language is very intuitive for creating interfaces ranging from prototype to production, especially for people with a background in web design and technologies. Unlike most other markup languages, XWT directly represents the instantiation of managed objects.
The benefices of XWT for e4 are following:
- More human-readable and light-weight markup without ambiguity between properties and child type
- High Extensible
- Well defined and complete specification
- Mature and Generic Declarative UI solution
Examples of XWT
1. Hello, world
Here is a simple example.
<Shell xmlns="http://www.eclipse.org/xwt/presentation" xmlns:x="http://www.eclipse.org/xwt"> <Shell.layout> <FillLayout/> </Shell.layout> <Button text="Hello, world!"> </Button> </Shell>
The same UI can be developed in Java corresponding:
Shell parent = new Shell(); parent.setLayout(new FillLayout()); Button button = new Button(parent, SWT.NONE); button.setText("Hello, world!");
To load and start a simple application, we use the class XWT:
Shell shell = (Shell) XWT.load(file)); shell.pack(); shell.open(); while (!shell.isDisposed()) { if (!shell.getDisplay().readAndDispatch()) { shell.getDisplay().sleep(); } }
Or simply
XWT.open(file));
It is possible to load a UI resource under a Composite:
XWT.load(parent, uri);
To use XWT, your Java project must import at least the following plugins
org.eclipse.swt org.eclipse.jface org.eclipse.e4.xwt org.eclipse.jface.databinding org.eclipse.core.databinding com.ibm.icu
2. Appearance and Event
In the previous example, we just rewrite Java code in XML. This example illustrates the separation between UI and event handling.
The appearance is defined in XWT.
<Shell xmlns="http://www.eclipse.org/xwt/presentation" xmlns:x="http://www.eclipse.org/xwt" x:Class="ui.EventHandler"> <Shell.layout> <GridLayout/> </Shell.layout> <Button text="Click Me!" SelectionEvent="clickButton"> </Button> </Shell>
The extension attribute x:Class declares the Java class to handle all events. The Button event is handled by clickButton method in the class ui.EventHandler. The association is setup during the loading:
package ui; import org.eclipse.swt.Event; import org.eclipse.swt.Button; public class EventHandler { protected void clickButton(Event event) { Button button = (Button )event.widget; button.setText("Hello, world!"); } }
When the button gets selected, the method clickButton is invoked to change the Button text to "Hello, world!".
3. Layout
<Composite xmlns="http://www.eclipse.org/xwt/presentation" xmlns:x="http://www.eclipse.org/xwt"> <Composite.layout> <GridLayout numColumns="2"/> </Composite.layout> <Label text="Hello, world"/> <Text x:style="BORDER"> <Text.layoutData> <GridData horizontalAlignment="FILL" grabExcessHorizontalSpace="true"/> </Text.layoutData> </Text> </Composite>
- The simple element name (<Composite>) corresponds to a class name.
- The qualified element name (i.g. <Composite.layout>) corresponds to a property defined by an element.
- The default namespace corresponds to system packages.
- User defined package can be declared as a namespace in the format: ”clr-namespace:<package>=<jar>”
This is functionally equivalent to:
Composite parent = new Composite(shell, SWT.NONE); parent.setLayout(new GridLayout(2, false); Label label = new Label(parent, SWT.NULL); label.setText("Hello, world"); Text text = new Text(parent, SWT.BORDER); text.setLayoutData(new GridData(GridData.FILL_HORIZONTAL | GridData.GRAB_HORIZONTAL));
4. Extensibility and Re-usability
In case, if you have your own layout named as ui.MyGridLayout, it can be used directly. The code will be:
<Composite xmlns="http://www.eclipse.org/xwt/presentation" xmlns:x="http://www.eclipse.org/xwt" xmlns:y="cls-namespace:ui"> <Composite.layout> <y:MyGridLayout numColumns="2"/> </Composite.layout> <Label text="Hello, world"/> <Text x:style="BORDER"> <Text.layoutData> <GridData horizontalAlignment="FILL" grabExcessHorizontalSpace="true"/> </Text.layoutData> </Text> </Composite>
In the same way, a customized UI component can be used directly:
<Composite xmlns="http://www.eclipse.org/xwt/presentation" xmlns:x="http://www.eclipse.org/xwt" xmlns:y="cls-namespace:ui"> <Composite.layout> <GridLayout numColumns="2"/> </Composite.layout> <y:PersonView /> <y:PersonView.layoutData> <GridData horizontalAlignment="FILL" grabExcessHorizontalSpace="true"/> </y:PersonView.layoutData> </y:PersonView> </Composite>
Where the ui.PersonView is a UI component developed by two files:
XWT file PersonView.xwt
<Composite xmlns="http://www.eclipse.org/xwt/presentation" xmlns:x="http://www.eclipse.org/xwt" x:Class="ui.PersonView" xmlns:y="cls-namespace:ui"> <Composite.layout> <GridLayout numColumns="2"/> </Composite.layout> <Label text="Name"/> <Text x:style="BORDER"> <Text.layoutData> <GridData horizontalAlignment="FILL" grabExcessHorizontalSpace="true"/> </Text.layoutData> </Text> </Composite>
Java class PersonView.java
package ui; import org.eclipse.swt.widgets.Composite; public class PersonView extends Composite { ... }
5. Data Binding
The DataBinding engine relies on Eclipse DataBinding component. To enable this feature, your Java project must import at least the following plugins
org.eclipse.swt org.eclipse.jface org.eclipse.e4.xwt org.eclipse.jface.databinding org.eclipse.core.databinding org.eclipse.core.databinding.beans org.eclipse.core.databinding.property com.ibm.icu
If we bind the text attribute of Label to a property “Name” of a Person, here is the data binding expression:
<Label text="{binding path=Name}"/>
It has the same result as following, but the expression is in pure XML:
<Label> <Label.text> <Binding path=”Name”/> </Label.text> <Label>
The data context of Label should be a person.
6. JFace integration
The following example shows the JFace direct integration with ListViewer.
We have a Class Company that has a name and a collection of Employee. The company is bound to the root Composite object. The child Text is bound to Name of company and ListViewer to property employees of type Java Collection.
<Composite xmlns="http://www.eclipse.org/xwt/presentation" xmlns:x="http://www.eclipse.org/xwt" xmlns:j="clr-namespace:jface.listviewer" x:DataContext="{StaticResource myCompany}"> <Composite.layout> <GridLayout numColumns="2"/> </Composite.layout> <x:Composite.Resources> <j:Company x:Key="myCompany" Name="Soyatec"> <j:Company.employees> <j:Employee Name="Thomas"/> <j:Employee Name="Jin"/> </j:Company.employees> </j:Company> </x:Composite.Resources> <Label text="Name"/> <Text text="{Binding Path=Name}"/> <ListViewer input="{Binding Path=employees}"> <ListViewer.contentProvider> <j:ContentProvider/> </ListViewer.contentProvider> <ListViewer.labelProvider> <j:LabelProvider/> </ListViewer.labelProvider> <ListViewer.control.layoutData> <GridData horizontalAlignment="FILL" grabExcessHorizontalSpace="true" horizontalSpan="2"/> </ListViewer.control.layoutData> </ListViewer> </Composite>