java @UiHandler 的文档
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Documentation for @UiHandler
提问by Roalt
I started to look into using GWT in combination with UiBuilder. I'm a bit puzzled about how you can use the @UiHandler(..)directive to make simple event handle code as written down in the GWT documentation:
我开始研究将 GWT 与 UiBuilder 结合使用。我对如何使用该@UiHandler(..)指令来制作GWT 文档中所写的简单事件句柄代码感到有些困惑：
@UiHandler("button")
void handleClick(ClickEvent e) {
Window.alert("Hello, AJAX");
}
In this case the method handleClickis used.
How do you know for each GWT widget what methods can be created with @UiHandler? For some you can also create a doClose()method.
在这种情况下，handleClick使用该方法。您如何知道每个 GWT 小部件可以使用哪些方法创建@UiHandler？对于某些人，您还可以创建一个doClose()方法。
But what can you use with, for instance, a ListBoxto get an event an item is selected? Where in the documentation can I see this?
但是，例如，您可以使用 aListBox来获取选择项目的事件吗？我可以在文档中的哪个位置看到这个？
回答by Igor Klimer
The parameter you pass to the @UiHandlerannotation is the name of the appropriate field you want to assign that *Handler. So, in this case you are assigning a ClickHandlerto a Button button(actually, we just know the field's name).
您传递给@UiHandler注释的参数是您要为其分配的适当字段的名称*Handler。因此，在这种情况下，您将 a 分配ClickHandler给 a Button button（实际上，我们只知道字段的名称）。
As for how this exactly works - it's part of GWT magic :) My guess is that, just like any other UiBinder related code (I think there was a presentation on Google IO, that showed the code that UiBinder generates), at compilation time the compiler figures out what goes where. In this example: we have a Button button, and we have a @UiHandlerannotated method that has a ClickEventparameter -> that mustmean it's a ClickHandler(notice that the method's name doesn'tmatter). So let's add some code at compile time (in the constructor, probably) that adds that handler to the button. If you are interested in a more comprehensive answer - check out the source :D
至于这究竟是如何工作的——它是 GWT 魔法的一部分 :) 我的猜测是，就像任何其他 UiBinder 相关代码一样（我认为 Google IO 上有一个演示文稿，展示了 UiBinder 生成的代码），在编译时编译器计算出什么去哪里。在这个例子中：我们有一个Button button，我们有一个@UiHandler带ClickEvent参数的带注释的方法->必须表示它是一个ClickHandler（注意方法的名称并不重要）。因此，让我们在编译时（可能在构造函数中）添加一些代码，将处理程序添加到按钮。如果您对更全面的答案感兴趣 - 查看来源：D
But what can you use with, for instance, a
ListBoxto get an event an item is selected? Where in the documentation can I see this?
但是，例如，您可以使用 a
ListBox来获取选择项目的事件吗？我可以在文档中的哪个位置看到这个？
In the GWT API reference. In this case, you are probably looking for ListBox.addChangeHandler. But you usually won't find @UiHandlerrelated code there - that's because it would be redundant - you always construct the @UiHandlermethods the same way:
在GWT API 参考中。在这种情况下，您可能正在寻找ListBox.addChangeHandler。但是你通常不会在@UiHandler那里找到相关的代码——那是因为它是多余的——你总是@UiHandler以相同的方式构造方法：
- You check the
*Handlerthat you want to add, sayChangeHandler It has a
void onChange(ChangeEvent event)- so, your method needs aChangeEventparameter and should look like this:@UiHandler("listBox") void whateverName(ChangeEvent event) { // ... }
- 你检查
*Handler你想要添加的，说ChangeHandler 它有一个
void onChange(ChangeEvent event)- 所以，你的方法需要一个ChangeEvent参数，应该是这样的：@UiHandler("listBox") void whateverName(ChangeEvent event) { // ... }
回答by Fabricio
Probably your problem is in your onModuleLoad method:
您的问题可能出在 onModuleLoad 方法中：
public void onModuleLoad()
{
HelloWorld helloWorld = new HelloWorld("BOTAO");
// Using this way @UiHandler will not work
//Document.get().getBody().appendChild(helloWorld.getElement());
// correct way
RootPanel.get().add(helloWorld);
}
