Question

我正在尝试使用mouseDragged编写一个绘制一行圆圈的程序，就像MS绘制一样。点击后，我已经成功获得了绘制圆圈的程序。当我拖动鼠标时，我也成功地让我的程序画圆圈;但是，这不会在我拖动的任何地方留下一圈圆圈。它只是拖动同一个圆圈。我试图让我的程序在我拖动的地方留下一些圆圈，但我很困惑为什么我的程序不会这样做。

package assignment_11;

import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.*;


public class Canvas extends JComponent implements MouseListener, MouseMotionListener{

private int x, x1;
private int y, y1;

public Canvas() {
    addMouseMotionListener(this);
    addMouseListener(this);
}

public static void main(String[] args) {
    //creates new JFrame, sets Exit On Close, sets visible
    JFrame window = new JFrame();
    window.add(new Canvas());
    window.pack();
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setVisible(true);
}

public Dimension getPreferredSize() {
    return new Dimension(640,480);
}

@Override
public void mouseClicked(MouseEvent arg0) {
    System.out.println(arg0);
    x = arg0.getX();
    y = arg0.getY();
    repaint();

}

@Override
public void mouseEntered(MouseEvent arg0) {
    System.out.println(arg0);

}

@Override
public void mouseExited(MouseEvent arg0) {
    System.out.println(arg0);

}

@Override
public void mousePressed(MouseEvent arg0) {
    System.out.println(arg0);

}

@Override
public void mouseReleased(MouseEvent arg0) {
    System.out.println(arg0);

}

public void paintComponent(Graphics g) {
    g.fillOval(x, y, 10, 10);
    g.fillOval(x1, y1, 10, 10);
}

@Override
public void mouseDragged(MouseEvent arg0) {
    System.out.println(arg0);
    x1 = arg0.getX();
    y1 = arg0.getY();
    repaint();
}

@Override
public void mouseMoved(MouseEvent arg0) {
    System.out.println(arg0);
}


}

感谢任何帮助！

Answer 1

绘画具有破坏性。也就是说，每次调用paintComponent时，都需要重新绘制组件的整个状态。

这引发了一个问题 - 每次调用paintComponent时，你需要一些方法来存储你想要绘制的状态。

为此，一个简单的ArrayList可以很好地完成工作。它允许您存储您感兴趣的所有点，并允许您在每次调用paintComponent时重新绘制它们，例如......

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class Canvas extends JComponent implements MouseListener, MouseMotionListener {

    private List<Point> points;

    public Canvas() {
        points = new ArrayList<>(25);
        addMouseMotionListener(this);
        addMouseListener(this);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater((new Runnable() {
            @Override
            public void run() {
                JFrame window = new JFrame();
                window.add(new Canvas());
                window.pack();
                window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                window.setVisible(true);
            }
        }));
    }

    public Dimension getPreferredSize() {
        return new Dimension(640, 480);
    }

    @Override
    public void mouseClicked(MouseEvent arg0) {
        System.out.println(arg0);
        points.add(arg0.getPoint());
        repaint();

    }

    @Override
    public void mouseEntered(MouseEvent arg0) {
        System.out.println(arg0);

    }

    @Override
    public void mouseExited(MouseEvent arg0) {
        System.out.println(arg0);

    }

    @Override
    public void mousePressed(MouseEvent arg0) {
        System.out.println(arg0);

    }

    @Override
    public void mouseReleased(MouseEvent arg0) {
        System.out.println(arg0);

    }

    public void paintComponent(Graphics g) {
        for (Point p : points) {
            g.fillOval(p.x, p.y, 10, 10);
        }
    }

    @Override
    public void mouseDragged(MouseEvent arg0) {
        System.out.println(arg0);
        points.add(arg0.getPoint());
        repaint();
    }

    @Override
    public void mouseMoved(MouseEvent arg0) {
        System.out.println(arg0);
    }

}

现在，随着问题复杂性的增加，您可以在List中存储“形状”，它们具有如何绘制自己的某种概念，允许添加更复杂的形状

你还应该看看Painting in AWT and Swing，以便更好地了解Swing中的绘画实际上是如何工作的

使用mouseDragged绘制圆圈的轨迹

1 个答案: