itemStateChanged on JButton

问题描述

我读到一个 JButton 实现 ItemSelectable ，并在文档中具有方法 addItemListener 所以我可以认为它可以生成一个 ItemEvent ...但是当我注册一个 JButton JMenuItem ）接口的事件没有增加？

为什么？ p>

我知道如果在文档中报告一个组件有一个添加....侦听器，这意味着它支持该事件...但是经验并不常见...

真相如何？

解决方案

一个按钮被按下（触发 ActionEvent ）和一个按钮被选择（触发 ItemEvent ）。默认情况下，一个 JButton 由$ code> javax.swing.DefaultButtonModel 支持。如果您在默认按钮模型中查看 setPressed 和 setSelected 方法，您将看到触发不同事件的代码

所以如果你以编程方式调用 JButton.setSelected ，你的项目监听器将被触发。如果您点击按钮，您将只会收到该操作事件。

另请注意，使用 JButton 不像说，一个 JToggleButton ），你可能不会在视觉上看到很多选择。

I read that a JButton implements ItemSelectable and into documentation it has the method addItemListener so I can argue that it can generate an ItemEvent... but when I register with a JButton (but also for a JMenuItem) that interface the event is not rised?

Why?

I understand that if into docs is reported that a component has an add....Listener it means that it support that event... but for experience isn't often so...

What's the truth?

解决方案

There is a difference between a button being "pressed" (which fires an ActionEvent) and a button being "selected" (which fires the ItemEvent). By default a JButton is backed by a javax.swing.DefaultButtonModel. If you look at the setPressed and setSelected methods in default button model you'll see the code that fires the different events.

So if you programmically call JButton.setSelected, your item listener will be fired. If you click the button, you'll only get the action event.

Note also that with a JButton (unlike, say, a JToggleButton) you probably won't see much visually when it is selected.

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