切换JPanel后,Java KeyListener没有响应

Question

当我在JPanel之间切换时,我遇到了KeyListener没有响应(由于没有获得焦点)的问题.

我有谷歌这个,并知道要解决这个问题,我需要使用KeyBindings,但我不喜欢KeyBindings.所以我想知道,还有其他方法吗？

这是JPanel的初始化代码,它具有无响应的KeyListener:

    public void init()
{
    setFocusable(true);
    requestFocusInWindow();
    requestFocus();
    addMouseListener(new MouseInput());
    addMouseMotionListener(new MouseInput());
    addMouseWheelListener(new MouseInput());
    addKeyListener(new KeyInput(p));

    t = new Timer(10, this);
    t.start();
}

如果需要,请随时索取更多代码示例!

Answer 1

在哈克解决方法是调用requestFocusInWindow()上JPanel,以确保它集中了KeyListener/ KeyAdapter现在增加了Componnet后这应该只能被称为(但可以肯定我的组件具有焦点我把它称为后JFrame通过刷新revalidate()和repaint()),例如:

public class MyUI {

    //will switch to the gamepanel by removing all components from the frame and adding GamePanel
    public void switchToGamePanel() {
        frame.getContentPane().removeAll();

        GamePanel gp = new GamePanel();//keylistener/keyadapter was added to Jpanel here

        frame.add(gp);//add component. we could call requestFocusInWindow() after this but to be 98%  sure it works lets call after refreshing JFrame

        //refresh JFrame
        frame.pack();
        frame.revalidate();
        frame.repaint();

        gp.requestFocusInWindow();
    }

}
class GamePanel extends JPanel { 

      public GamePanel() {
          //initiate Jpanel and Keylistener/adapter
      }

}

但是你应该使用Swing KeyBindings(+1到@Reimeus评论).

在这里阅读以熟悉它们:

• 如何使用键绑定

现在你已经阅读了,让我们展示另一个例子来帮助澄清(尽管Oracle做得很好)

如果我们想要一个添加KeyBinding到某个JComponent即JButton对Esc你会怎么做:

void addKeyBinding(JComponent jc) {
        jc.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0, false), "esc pressed");
        jc.getActionMap().put("esc pressed", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                System.out.println("Esc pressed");
            }
        });

        jc.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0, true), "esc released");
        jc.getActionMap().put("esc released", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                System.out.println("Esc released");
            }
        });
}

上面的方法将被称为:

JButton b=..;//create an instance of component which is swing

addKeyBinding(b);//add keybinding to the component

请注意:

1)你不需要两者KeyBindings,我只是展示了如何获得不同的关键状态并采取适当的行动Keybindings.

2)此方法将添加一个Keybinding只要Esc按下并且组件在具有焦点的窗口中就会被激活的方法,您可以通过指定另一个来改变它,InputMap即:

jc.getInputMap(JComponent.WHEN_FOCUSED).put(..);//will only activated when component has focus