无法在 JFrame 的构造函数之外将 JPanel 添加到 JLayeredPane

Question

我想在用户单击输入时将 JPanel 添加到 JLayeredPane，但 JPanel 未显示。如果我在 JFrame 的构造函数中将 JPanel 添加到 JLayeredPane，则一切正常。

当用户单击 'enter' 时，JPanel 正在显示，我该怎么办？

代码如下：

import java.awt.BorderLayout;
import java.awt.Color;
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.JComponent;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
import javax.swing.KeyStroke;

public class Test extends javax.swing.JFrame {

    public static void main(String[] args) {
        Test test = new Test();
        test.setSize(800, 500);
        test.setVisible(true);
    }

    public Test() {
        setLayout(new BorderLayout());

        //LayeredPane on JFrame
        JLayeredPane jlp = new JLayeredPane();
        jlp.setLayout(new BorderLayout());
        this.add(jlp, BorderLayout.CENTER);

        //Adds a JPanel to the North
        JPanel jPNorth = new JPanel();
        jPNorth.setBackground(Color.RED);
        jlp.add(jPNorth, BorderLayout.NORTH, JLayeredPane.DEFAULT_LAYER);

        //Adds Enter Keybinding
        InputMap key_input_map = jlp.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
        ActionMap key_action_map = jlp.getActionMap();

        key_input_map.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, 0, false), "add_jpanel");

        key_action_map.put("add_jpanel", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {

                JPanel jPSouth = new JPanel();
                jPSouth.setBackground(Color.YELLOW);
                jlp.add(jPSouth, BorderLayout.SOUTH, JLayeredPane.DEFAULT_LAYER);

                System.out.println("enter");
            }
        });
    }
}

谢谢，重麻五郎

Answer 1

你做的都对，解决方法很简单。当你动态添加 swing Components 时，你必须使用 component.repaint(); 和 component.revalidate(); 来重绘元素。添加完所有内容后添加这两个命令。因此，您的 actionPerformed 方法应更改为以下内容：

public void actionPerformed(ActionEvent e) {
    JPanel jPSouth = new JPanel();
    jPSouth.setBackground(Color.YELLOW);
    jlp.add(jPSouth, BorderLayout.SOUTH, JLayeredPane.DEFAULT_LAYER);
    //Need these to here!
    jlp.repaint();
    jlp.revalidate();
    System.out.println("enter");
}

无法在 JFrame 的构造函数之外将 JPanel 添加到 JLayeredPane

JPanel can't be added to JLayeredPane outside the JFrame's constructor

java

invisible

jpanel

jframe

jlayeredpane