java - 除非先单击 JButton，否则 keyPressed 不起作用

Question

我创建了一个使用 JButtons 来增加数字的小应用程序。这些按钮不应该是可单击的，而是可以通过键盘激活(即文本字段中的数字随着键盘的按下而增加，而不是通过使用鼠标单击按钮来增加)。我的问题是，当应用程序首次启动时，键盘不会执行任何操作，直到我第一次单击其中一个按钮 - 即使单击该按钮不会进行任何操作。我试图将其中一个按钮 requestFocusInWindow() 认为如果它已经被聚焦，那么按键就会起作用，但无论我将它放在我的主方法还是 Controller 类中，这似乎都不起作用。我试图弄清楚我是否需​​要执行 KeyboardFocusManager 或 addFocusListener() (但我不希望在按钮获得/失去焦点时总是发生某些事情)。我已经尝试了很多事情，我的头在旋转，试图将框架或 Controller 类添加到我的主要方法中。以下是我当前的代码:

带有 Main 的类

import javax.swing.JFrame;

public class Count {

    public static void main(String[] args) {
        CountController frame = new CountController();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(560, 150); 
        frame.setVisible(true); 
        //I've tried to add the button and requestFocusInWindow here
        //as well as tried a frame.addWindowFocusListener
    }
} // end class

Controller 类

imports ...
public class CountController extends JFrame implements KeyListener {
    private JLabel ...
    private JTextField ...
    private JButton ....
    int ...
    // no-argument constructor
    public CountController() {
        super("Title");
        setLayout(null); // position GUI components explicitly

        //set up JLabels in following manner
        label = new JLabel("some label");
        label.setBounds(47, 5, 45, 25);
        label.setHorizontalAlignment(JLabel.CENTER);
        add(label);

        //set up JTextFields in following manner
        textField = new JTextField("0");
        textField.setBounds(47, 30, 45, 25);
        textField.setHorizontalAlignment(JTextField.CENTER);
        textField.setBackground(Color.WHITE);
        textField.setEditable(false);
        add(textField);

        //set up JButtons in the following manner
        button = new JButton("some text");
        button.setBounds(15, 70, 110, 25);
        button.setBackground(Color.WHITE);
        add(button);
        button.addKeyListener(this);
        //I've tried adding requestFocusInWindow() here as well
    } // end constructor

    //begin KeyListener stuff
    @Override
    public void keyPressed(KeyEvent event){
        int keyCode = event.getKeyCode();
        switch(keyCode){
            case #: //# is ASCII #
                do some things;
                call a method();
                break;
        }
    }
    @Override
    public void keyReleased(KeyEvent event){
        button.setBackground(Color.WHITE);
    }
    @Override
    public void keyTyped(KeyEvent event){
        // nothing but this is needed for implementing KeyListener
    }

    //List of methods that are called from switch
        ...

    //I've tried to add a public void initialize(){}

}//end CountController class

如果您能提供任何有关使其正常工作的意见，我将不胜感激，这样我就不必在按键工作之前先单击按钮。谢谢!

Answer 1

为了让监听器触发事件​​，其注册的组件必须首先获得焦点并拥有焦点。使用key bindings API相反。

以下内容使用 JComponent.WHEN_IN_FOCUSED_WINDOW 定义将生成按键事件的上下文。在此配置中，无论焦点是什么，只要窗口当前处于焦点状态，事件仍然会生成

import java.awt.Color;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.KeyStroke;

public class Count {

  public static void main(String[] args) {
    CountController frame = new CountController();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(560, 150);
    frame.setVisible(true);
    //I've tried to add the button and requestFocusInWindow here
    //as well as tried a frame.addWindowFocusListener
  }

  public static class CountController extends JFrame {

    // no-argument constructor
    public CountController() {
      super("Title");
      setLayout(new GridBagLayout());
      GridBagConstraints gbc = new GridBagConstraints();
      gbc.gridwidth = GridBagConstraints.REMAINDER;

      //set up JLabels in following manner
      JLabel label = new JLabel("some label");
      label.setHorizontalAlignment(JLabel.CENTER);
      add(label, gbc);

      //set up JTextFields in following manner
      JTextField textField = new JTextField("0", 20);
      textField.setHorizontalAlignment(JTextField.CENTER);
      textField.setBackground(Color.WHITE);
      textField.setEditable(false);
      add(textField, gbc);

      //set up JButtons in the following manner
      JButton button = new JButton("some text");
      add(button, gbc);

      InputMap im = button.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
      ActionMap am = button.getActionMap();

      im.put(KeyStroke.getKeyStroke(KeyEvent.VK_3, KeyEvent.SHIFT_DOWN_MASK), "Pressed.#");
      am.put("Pressed.#", new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
          textField.setText(textField.getText() + "#");
        }
      });

    } // end constructor

  }//end CountController class
} // end class

虽然我会注册针对父容器的绑定(bind)而不是按钮，但这只是我的想法。

并且，不使用 null 布局的原因...这就是您的原始代码在我的电脑上的样子