java - 如何修改JPanel

Question

我尝试更改 JPanel。我的主课

public class Main {
        public static void main(String[] args) {
            MyFrame frame = new MyFrame();
        }
    }

MyFrame 类。这里我添加JPanel并实现ActionListener

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;

public class MyFrame extends JFrame implements ActionListener{
    MyPanel myPanel;
    JButton myButton = new JButton("reset");
    public MyFrame(){
        this.setSize(300, 500);
        this.setLayout(new BorderLayout());

        myButton.addActionListener(this);
        this.add(myButton, BorderLayout.SOUTH);

        myPanel = new MyPanel();
        myPanel.setButtons(3);

        this.add(myPanel, BorderLayout.CENTER);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent event) {
        if (event.getSource().equals(myButton)){
            System.out.println("click");
            this.remove(myPanel);
            myPanel.setButtons(5);
            this.add(myPanel, BorderLayout.CENTER);
            //I want to change number of buttons on MyPanel to 5
        }
    }
}

和MyPanel类

public class MyPanel extends JPanel{
    JButton[] buttons;
    public MyPanel(){
        this.setLayout(new FlowLayout());
    }

    public void setButtons(int x){
        buttons = new JButton[x];
        this.removeAll();
        for (int i = 0; i < x; i++){
            buttons[i] = new JButton(i+"");
            this.add(buttons[i]);
        }
    }
}

我期望的是在单击“重置”按钮后我想要更改 JPanel(删除三个现有按钮并添加五个)。它会改变，但只有在我调整窗口大小之后。为什么？

Answer 1

您需要告诉框架在更改组件后它应该重新进行布局。因此，在我们的操作监听器方法中添加一行:

    public void actionPerformed( ActionEvent event ) {
        if ( event.getSource().equals( myButton ) ) {
            System.out.println( "click" );
            this.remove( myPanel );
            myPanel.setButtons( 5 );
            this.add( myPanel, BorderLayout.CENTER );
            revalidate(); // <-- tell frame to update!
        }
    }