ListBox.java 文件源码

@Override
public HandlerRegistration addValueChangeHandler( ValueChangeHandler<T> handler )
{
    if( !registered )
    {
        registered = true;
        list.addChangeHandler( new ChangeHandler()
        {
            @Override
            public void onChange( ChangeEvent event )
            {
                ValueChangeEvent.fire( ListBox.this, getValue() );
            }
        } );
    }
    return addHandler( handler, ValueChangeEvent.getType() );
}