不要在GWT

Question

我创建了课程：

StcDragSource：

public class StcDragSource extends DragSource {
public StcDragSource(Component component) {
    super(component);
}

public StcDragSource(Component component, Component handler) {
    super(component);

    draggable = new Draggable(component, handler);
    draggable.setUseProxy(true);
    draggable.setSizeProxyToSource(false);
    draggable.setMoveAfterProxyDrag(false);
    draggable.addDragListener(listener);
}
}

StcDragSourceFe：

class StcDragSourceFe extends StcDragSource {

        public StcDragSourceFe(Component component, Component handler) {
            super(component, handler);
        }

        public StcDragSourceFe(Component component) {
            super(component);
            com.google.gwt.user.client.Window.alert("StcDragSourceFe");
            component.getElement().setDraggable(com.google.gwt.dom.client.Element.DRAGGABLE_TRUE);
        }

        @Override
        protected void onDragStart(DNDEvent event) {
            com.google.gwt.user.client.Window.alert("onDragStart");
            designer.setSelectionEnabled(false);
            event.setData(event.getDragSource().getComponent());
            event.getStatus().update("");
        }

        @Override
        protected void onDragCancelled(DNDEvent event) {
            com.google.gwt.user.client.Window.alert("onDragCancelled");
            super.onDragCancelled(event);
            designer.setSelectionEnabled(true);
        }

        @Override
        protected void onDragDrop(DNDEvent event) {
            super.onDragDrop(event);
            com.google.gwt.user.client.Window.alert("onDragDrop");
            Component c = (Component) event.getData();
            designer.setSelectionEnabled(true);
    }

当Component is Button拖放工作完美，但组件为Text时，不会创建处理程序，拖放也不起作用。

这个问题的原因是什么？