自定义ValueChangeHandler GWT [英] Custom ValueChangeHandler GWT

问题描述

我需要编写一个自定义 ValueChangeHandler 并调用 onValueChange（ValueChangeEvent）。但我不明白如何编写 ValueChangeEvent 。

可能我理解整个GWT事件系统是错误的。任何人都可以提供帮助吗？

编辑：我在问如何创建自己的派发ValueChangeEvent的类。我知道如何听它。

ValueChangeEvent的构造函数不可见，我无法创建它。

解决方案

如果您想触发 ValueChangeEvent ，您必须实现接口 HasValueChangeHandlers



一个简单的实现就是使用EventBus：



  EventBus bus = new SimpleEventBus（）; 
 
 @Override 
 public void fireEvent（GwtEvent<？> event）{
 bus.fireEvent（event）; 
 
 $ b @Override 
 public HandlerRegistration addValueChangeHandler（ValueChangeHandler< T>处理程序）{
 return bus.addHandler（ValueChangeEvent.getType（），handler）; 
 
  

请注意，您需要替换 T


由于您无法直接创建ValueChangeEvent，因此通过fire方法调度事件：

  ValueChangeEvent.fire（this，value）; 
  

其中这个指向类/字段实现 HasValueChangeHandlers 和值指的是已更改的值，并且您想分派该事件。

I need to write a custom ValueChangeHandler and call out onValueChange(ValueChangeEvent). However I don't understand how to write a ValueChangeEvent.

Maybe I understand the entire GWT event system wrong. Can anyone help?

Edit: I am asking how to create my own class that dispatches the ValueChangeEvent. I understand how to listen to it.

The constructor of ValueChangeEvent is not visible and I can't create it.

解决方案

If you want to fire a ValueChangeEvent you must implement the interface HasValueChangeHandlers by or your class or somewhere in the class.

A simple implementation would be to use the EventBus:

EventBus bus = new SimpleEventBus();

@Override
public void fireEvent(GwtEvent<?> event) {
    bus.fireEvent(event);
}

@Override
public HandlerRegistration addValueChangeHandler(ValueChangeHandler<T> handler) {
    return bus.addHandler(ValueChangeEvent.getType(), handler);
}

Note you need to substitute T with the type you want to fire.

Because you can't create a ValueChangeEvent directly dispatching an event is done via the fire method:

ValueChangeEvent.fire(this, value);

Where this refers to the class/field implementing the HasValueChangeHandlers and value refers to the value that has been changed and you want to dispatch the event.

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