java - 使用 Keybind 和 MouseInfo 获取 Label

Question

这是我之前 question. 的后续问题

我有两个 JPanels，每个有 5 个 JLabels。当我将鼠标悬停在其中一个 JLabels 上并按下删除键时，我想打印标签的文本。这是我尝试过的:

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.PointerInfo;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;

import javax.swing.*;

@SuppressWarnings("serial")
public class KeybindExample extends JPanel {

   public KeybindExample() {
      setLayout(new BorderLayout());
      add(firstRow(), BorderLayout.NORTH);
      add(secondRow(),BorderLayout.SOUTH);
      int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = getInputMap(condition);
      ActionMap actionMap = getActionMap();

      KeyStroke delKeyStroke = KeyStroke.getKeyStroke(KeyEvent.VK_DELETE, 0);
      String delete = "delete";

      inputMap.put(delKeyStroke, delete);
      actionMap.put(delete, new DeleteAction());
   }

   private class DeleteAction extends AbstractAction {
      @Override
      public void actionPerformed(ActionEvent evt) {
         PointerInfo pInfo = MouseInfo.getPointerInfo();
         Point ptOnScrn = pInfo.getLocation();
         int xPanel = getLocationOnScreen().x;
         int yPanel = getLocationOnScreen().y;
         int x = ptOnScrn.x - xPanel;
         int y = ptOnScrn.y - yPanel;

         Component component = getComponentAt(x, y);
         if (component != null) {
             JLabel selectedLabel = (JLabel) component;
             System.out.println("Selected Label: " + selectedLabel.getText());
          }
      }
   }
   private static JPanel firstRow(){
        JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
        String [] x = {"1","2","3","4","5"};
        for(int i = 0; i < 5; i++){
            JLabel label = new JLabel(x[i]);
            label.setPreferredSize(new Dimension(50,50));
            panel.add(label);
        }

        return panel;
   }
   private static JPanel secondRow(){
        JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
        String [] x = {"6","7","8","9","10"};
        for(int i = 0; i < 5; i++){
            JLabel label = new JLabel(x[i]);
            label.setPreferredSize(new Dimension(50,50));
            panel.add(label);
        }

        return panel;
   }

   private static void createAndShowGui() {
      KeybindExample mainPanel = new KeybindExample();

      JFrame frame = new JFrame("Key Bindings Example");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

我收到以下错误:

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: javax.swing.JPanel cannot be cast to javax.swing.JLabel

如果我理解正确的话，我有一个 JPanel(KeybindExample)，它包含两个 JPanel，而这两个 JPanel 中的每一个包含 JLabels。因此，当我执行 getComponentAt(x,y) 时，我得到的组件是另一个导致类型转换问题的 JPanel 。

我认为我需要做的是获取 Component At (x,y) 的组件，这将是一个 JLabel。换句话说，我需要更进一步。我尝试了以下方法，但它仅适用于顶部面板，有时仍会返回相同的错误。

     Component component = getComponentAt(x, y);
     if (component != null) {
        JPanel selectPanel = (JPanel) component;
        Component comp = selectPanel.getComponentAt(x,y);

        if(comp != null){
           JLabel selectLabel = (JLabel) comp;
           System.out.println("Selected Label: " + selectLabel.getText());
        }
     }
  }

我怎样才能拥有包含多个 JLabel 的多个 JPanel，但能够让 JLabel 将鼠标悬停在文本上。

Answer 1

关键问题是——如何在某个时间点获取对所需 JLabel 的引用，此时您按下删除键。您当前的解决方案(我之前提出的解决方案)不起作用，因为代码找到了相对于 KeybindExample JPanel 的当前组件，因为这是您调用的组件 getComponentAt()方法上。一种可能的解决方案是调用 getComponentAt()在实际持有 JLabel 的 JPanel 上。另一种可能的解决方案是计算鼠标相对于每个 JLabel 的位置，并使用 contains(...)方法来查看鼠标是否位于 JLabel 之一上。为此，您需要有权访问所有 J​​Label，或许可以将它们放在 List<JLabel> 中。 .例如……

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.PointerInfo;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import java.util.List;

import javax.swing.*;

@SuppressWarnings("serial")
public class KeybindExample extends JPanel {
   private List<JLabel> labelList = new ArrayList<>();

   public KeybindExample() {
      setLayout(new BorderLayout());
      add(firstRow(), BorderLayout.NORTH);
      add(secondRow(), BorderLayout.SOUTH);
      int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = getInputMap(condition);
      ActionMap actionMap = getActionMap();

      KeyStroke delKeyStroke = KeyStroke.getKeyStroke(KeyEvent.VK_DELETE, 0);
      String delete = "delete";

      inputMap.put(delKeyStroke, delete);
      actionMap.put(delete, new DeleteAction());
   }

   private class DeleteAction extends AbstractAction {
      @Override
      public void actionPerformed(ActionEvent evt) {
         PointerInfo pInfo = MouseInfo.getPointerInfo();
         Point ptOnScrn = pInfo.getLocation();

         for (JLabel label : labelList) {
            int x = ptOnScrn.x - label.getLocationOnScreen().x;
            int y = ptOnScrn.y - label.getLocationOnScreen().y;

            if (label.contains(x, y)) {
               System.out.println("Selected Label: " + label.getText());
            }

         }
         // int xPanel = getLocationOnScreen().x;
         // int yPanel = getLocationOnScreen().y;
         // int x = ptOnScrn.x - xPanel;
         // int y = ptOnScrn.y - yPanel;
         //
         // Component component = getComponentAt(x, y);
         // if (component != null) {
         // JLabel selectedLabel = (JLabel) component;
         // System.out.println("Selected Label: " + selectedLabel.getText());
         // }
      }
   }

   private JPanel firstRow() {
      JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
      String[] x = { "1", "2", "3", "4", "5" };
      for (int i = 0; i < 5; i++) {
         JLabel label = new JLabel(x[i]);
         labelList.add(label);
         label.setPreferredSize(new Dimension(50, 50));
         panel.add(label);
      }

      return panel;
   }

   private JPanel secondRow() {
      JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
      String[] x = { "6", "7", "8", "9", "10" };
      for (int i = 0; i < 5; i++) {
         JLabel label = new JLabel(x[i]);
         labelList.add(label);
         label.setPreferredSize(new Dimension(50, 50));
         panel.add(label);
      }

      return panel;
   }

   private static void createAndShowGui() {
      KeybindExample mainPanel = new KeybindExample();

      JFrame frame = new JFrame("Key Bindings Example");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}