Recipe 8.9 Creating Composite Widgets

     

8.9.1 Problem

To create your own custom widget, you need to create a widget that contains other widgets.

8.9.2 Solution

Use a container widget such as a composite widget to create an object from the Composite class. Then add widgets to the composite object as you would to a Shell object.

8.9.3 Discussion

A number of widgets, such as composite widgets, are designed to hold other widgets, which enables you to build composite widgets. Example 8-7 displays a composite widget ( CompositeApp at this book's site). In this case, we'll display the same labels that we displayed using a grid layout, but in a shell in a composite widget instead. First, we create a composite widget and install a grid layout in it:

 final Composite composite = new Composite(shell, SWT.NONE); GridLayout gridLayout = new GridLayout( ); gridLayout.numColumns = 4; composite.setLayout(gridLayout); 

Now treat the composite widget as a container, just like a shell, and add the label widgets to it, as shown in Example 8-7.

Example 8-7. Using composite widgets

 package org.cookbook.ch08; import org.eclipse.swt.*; import org.eclipse.swt.layout.*; import org.eclipse.swt.widgets.*; public class CompositeClass {     public static void main (String [] args) {         Display display = new Display ( );         final Shell shell = new Shell (display);         shell.setSize(300, 300);         shell.setLayout(new RowLayout( ));                  shell.setText("Composite Example");                  final Composite composite = new Composite(shell, SWT.NONE);         GridLayout gridLayout = new GridLayout( );         gridLayout.numColumns = 4;         composite.setLayout(gridLayout);  sfor (int loopIndex = 0; loopIndex < 28; loopIndex++) {             Label label = new Label(composite, SWT.SHADOW_NONE);             label.setText("Label " + loopIndex);         }  shell.open ( );         while (!shell.isDisposed( )) {             if (!display.readAndDispatch( )) display.sleep( );         }         display.dispose ( );     } } 

The composite widget holding the labels appears in the shell, as shown in Figure 8-8.

Figure 8-8. Using a composite widget

Besides composite widgets, other widgets that can contain widgets include canvases (designed for drawing) and groups (which can display borders as well).