Bug 136256 Enhance the message builder
Please see the spec attached in 133995 for detail.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ImageBuilder.java
previewArea.setLayoutData( gd );
		previewArea.setLayout( new FillLayout( ) );
		previewCanvas = new ImageCanvas( previewArea );
	}
	private void switchTo( int type )
	{
		if ( type == selectedType )
		{
			return;
		}
		selectedType = type;
		Control[] controls = inputArea.getChildren( );
		for ( int i = 0; i < controls.length; i++ )
		{
			controls[i].dispose( );
		}
		clearPreview( );
		switch ( type )
		{
			case URI_TYPE :
				swtichToExprType( );
				break;
			case EMBEDDED_TYPE :
				swtichToEmbeddedType( );
				break;
			case BLOB_TYPE :
				swtichToExprType( );
				break;
		}
		inputArea.layout( );