The client-side components, or in GWT terminology, widgets, must be made usable in the client-side GWT application by defining a widget set factory that can create the widgets by their UIDL tag name. The widget set class needs to inherit the DefaultWidgetSet class and implement the createWidget() and resolveWidgetTypeName() methods. The methods must call the default implementation to allow creation of the standard widgets.

The following example shows how to define a widget set factory class for the Color Picker example. The tag name of the widget was defined in the server-side implementation of the widget (see the section called “Example: A Color Picker GWT Widget”) as colorpicker. The resolveWidgetTypeName() must resolve it to the full name of the ItkColorPicker integration class. The createWidget() method must create a ItkColorPicker object when it receives this name.

package com.itmill.toolkit.demo.colorpicker.gwt.client;

import com.google.gwt.user.client.ui.Widget;
import com.itmill.toolkit.demo.colorpicker.gwt.client.ui.ItkColorPicker;
import com.itmill.toolkit.terminal.gwt.client.DefaultWidgetSet;
import com.itmill.toolkit.terminal.gwt.client.UIDL;

public class WidgetSet extends DefaultWidgetSet {
    /** Creates a widget according to its class name. */
    public Widget createWidget(UIDL uidl) {
        String className = resolveWidgetTypeName(uidl);
        if ("com.itmill.toolkit.demo.colorpicker.gwt.client.ui.ItkColorPicker"
            .equals(className))
            return new ItkColorPicker();

        // Let the DefaultWidgetSet handle creation of default widgets
        return super.createWidget(uidl);
    }

    /** Resolves UIDL tag name to class name. */
    protected String resolveWidgetTypeName(UIDL uidl) {
        String tag = uidl.getTag();
        if ("colorpicker".equals(tag))
            return "com.itmill.toolkit.demo.colorpicker.gwt.client.ui.ItkColorPicker";

        // Let the DefaultWidgetSet handle resolution of default widgets
        return super.resolveWidgetTypeName(uidl);
    }
}

The default widgets in IT Mill Toolkit actually use more than just the tag name to resolve the actual widget class. For example, the Button server-side component, which as tag name button, can be resolved to either an IButton or ICheckBox widget, depending on the switch (switchMode) attribute. IT Mill Toolkit Client-Side Engine can actually replace the client-side object of the parameters change.

<module>
    <!-- Inherit the NoEntry version to avoid multiple entrypoints -->
    <inherits name="com.itmill.toolkit.terminal.gwt.DefaultWidgetSetNoEntry" /> 
    
    <!-- WidgetSet default theme -->    
    <stylesheet src="colorpicker/styles.css"/>

    <!-- Entry point -->
    <entry-point class="com.itmill.toolkit.demo.colorpicker.gwt.client.WidgetSet"/>
  
</module>