java - 如何访问外部类的公共(public)方法以便在 JPanel 上重绘？

Question

我无法访问扩展 JPanel 的类 MyPanel 的公共(public)方法。在 MyPanel 中，我之前有一个名为 moveSquare 的 private 方法，但为了使其适用于外部请求，我将其更改为 public ，但还是不行？如何让它发挥作用？

import javax.swing.SwingUtilities;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.BorderFactory;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseMotionListener;
import java.awt.event.MouseMotionAdapter;

public class mull {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JPanel p = createAndShowGUI();
                iterate(p);
                // "The method iterate(MyPanel) in the type mull is not applicable for the arguments (JPanel)"
            }
        });
    }

    private static JPanel createAndShowGUI() {
        System.out.println("Created GUI on EDT? "+
        SwingUtilities.isEventDispatchThread());
        JFrame f = new JFrame("Swing Paint Demo");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        // how to grab link to this panel - in order to use it in iteration loop ?
        MyPanel p = new MyPanel();
        f.add(p);
//        f.add(new MyPanel());
        f.pack();
        f.setVisible(true);
        return p;
    } 
    private static void iterate(JPanel p){
        // the loop should change square position on each iteration
        // how to implement ?

        for (int i  = 0; i < 999; i++){
            ((MyPanel) p).moveSquare(100 + i*10, 200 + i*10); // here is problem: 
            //"Cannot make a static reference to the non-static method moveSquare(int, int) from the type MyPanel"
        }


    }
}

class MyPanel extends JPanel {

    private int squareX = 50;
    private int squareY = 50;
    private int squareW = 200;
    private int squareH = 200;

    public MyPanel() {

        setBorder(BorderFactory.createLineBorder(Color.black));

        addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                moveSquare(e.getX(),e.getY());
            }
        });

        addMouseMotionListener(new MouseAdapter() {
            public void mouseDragged(MouseEvent e) {
                moveSquare(e.getX(),e.getY());
            }
        });

    }
    // originally this method was private - in orger to access it within mull, it vas changed to public
    public void moveSquare(int x, int y) {
        int OFFSET = 1;
        if ((squareX!=x) || (squareY!=y)) {
            repaint(squareX,squareY,squareW+OFFSET,squareH+OFFSET);
            squareX=x;
            squareY=y;
            repaint(squareX,squareY,squareW+OFFSET,squareH+OFFSET);
        } 
    }


    public Dimension getPreferredSize() {
        return new Dimension(900,700);
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);       
        g.drawString("This is my custom Panel!",10,20);
        g.setColor(Color.RED);
        g.fillRect(squareX,squareY,squareW,squareH);
        g.setColor(Color.BLACK);
        g.drawRect(squareX,squareY,squareW,squareH);
    }  
}

此语法的作用 ((MyPanel) p).moveSquare(100 + i*10, 200 + i*10); ？如何在 iterate(p) 中绘制自定义形状(椭圆)？

Answer 1

您似乎甚至没有调用 iterate()。

但在任何情况下，您的 moveSquare 方法都不是静态的，因此需要特定的 MyPanel 实例才能运行。因此，您可能希望保留对面板的引用。比方说，您可以使用:

而不是 f.add(new MyPanel())

MyPanel p = new MyPanel();
f.add(p);

然后将 p 传递给 iterate 并在其中调用 p.moveSquare(100,200)。