你如何在 Java 中将 ActionListener 添加到 JButton 上 [英] How do you add an ActionListener onto a JButton in Java

问题描述

private JButton jBtnDrawCircle = new JButton("Circle");
private JButton jBtnDrawSquare = new JButton("Square");
private JButton jBtnDrawTriangle = new JButton("Triangle");
private JButton jBtnSelection = new JButton("Selection");

如何向这些按钮添加动作侦听器，以便从主方法中我可以对它们调用 actionperformed，以便在单击它们时我可以在我的程序中调用它们?

How do I add action listeners to these buttons, so that from a main method I can call actionperformed on them, so when they are clicked I can call them in my program?

推荐答案

两种方式:

1. 在你的类中实现 ActionListener，然后使用 jBtnSelection.addActionListener(this); 之后，你必须定义一个方法，public voidactionPerformed(ActionEvent e).但是，对多个按钮执行此操作可能会令人困惑，因为 actionPerformed 方法必须检查每个事件的源 (e.getSource()) 以查看它是哪个按钮来自.

1. Implement ActionListener in your class, then use jBtnSelection.addActionListener(this); Later, you'll have to define a menthod, public void actionPerformed(ActionEvent e). However, doing this for multiple buttons can be confusing, because the actionPerformed method will have to check the source of each event (e.getSource()) to see which button it came from.

2. 使用匿名内部类:

jBtnSelection.addActionListener(new ActionListener() { 
  public void actionPerformed(ActionEvent e) { 
    selectionButtonPressed();
  } 
} );

稍后，您必须定义selectionButtonPressed().当您有多个按钮时，这会更有效，因为您对处理操作的各个方法的调用就在按钮的定义旁边.

Later, you'll have to define selectionButtonPressed(). This works better when you have multiple buttons, because your calls to individual methods for handling the actions are right next to the definition of the button.

2，更新.由于 Java 8 引入了 lambda 表达式，您可以说与 #2 基本相同的内容，但使用更少的字符:

2, Updated. Since Java 8 introduced lambda expressions, you can say essentially the same thing as #2 but use fewer characters:

jBtnSelection.addActionListener(e -> selectionButtonPressed());

在这种情况下，e 是 ActionEvent.这是有效的，因为 ActionListener 接口只有一个方法，actionPerformed(ActionEvent e).

In this case, e is the ActionEvent. This works because the ActionListener interface has only one method, actionPerformed(ActionEvent e).

第二种方法还允许您直接调用selectionButtonPressed 方法.在这种情况下，如果发生其他一些操作，您也可以调用 selectionButtonPressed() - 例如，当计时器关闭时或其他情况(但在这种情况下，您的方法将被命名为不同的名称，也许 <代码>selectionChanged()).

The second method also allows you to call the selectionButtonPressed method directly. In this case, you could call selectionButtonPressed() if some other action happens, too - like, when a timer goes off or something (but in this case, your method would be named something different, maybe selectionChanged()).

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