SelectOneListBox.java 文件源码

@Override
public HandlerRegistration addValueChangeHandler(ValueChangeHandler<T> handler)
{
    // Initialization code
    if (!valueChangeHandlerInitialized)
    {
        valueChangeHandlerInitialized = true;
        super.addChangeHandler(new ChangeHandler()
        {
            public void onChange(ChangeEvent event)
            {
                ValueChangeEvent.fire(SelectOneListBox.this, getValue());
            }
        });
    }
    return addHandler(handler, ValueChangeEvent.getType());
}