我正在尝试构建一个简单的绘画工具。 mouseDrag 事件创建了一个新的椭圆并使我的 JPanel 变为 repaint()。

到目前为止一切正常。 但是，如果我在第一次触发 mouseDrag 事件之前按下任何按钮(或任何其他 UI 组件)，该按钮将绘制在面板的左上角。

我已将代码隔离到此测试应用程序中:

import java.awt.BasicStroke;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Test extends JFrame
{
    public Test()
    {
        final JPanel paintPanel = new JPanel(){
            @Override
            protected void paintComponent(Graphics g)
            {
                Graphics2D g2d = (Graphics2D)g;
                g2d.setPaintMode();

                g2d.setStroke(new BasicStroke(1));
                g2d.fillRect(100, 100, 10, 10);
            }
        };

        paintPanel.setPreferredSize(new Dimension(300,300));
        paintPanel.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e)
            {
                paintPanel.repaint();
            }
        });

        this.setLayout(new FlowLayout());

        this.add(paintPanel);
        this.add(new JButton("Dummy"));

        this.pack();
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
    }

    public static void main(String... args)
    {
        new Test();
    }
}

A Screenshot for "seeing" the problem in my Main application

最佳答案

+1 @MadProgrammer 的回答。

• 您应该将 super.paintComponent(..) 作为覆盖 paintComponent() 的第一个调用
• 不要不必要地扩展JFrame
• 通过 EDT 创建和最小化 Swing 组件
• 不要调用 setPrefferedSize() 而是覆盖 getPrefferedSize()

这是一个结合了我的建议和@MadProgrammer 的建议的示例:

import java.awt.BasicStroke;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Test {

    JFrame frame;

    public Test() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final PaintPanel paintPanel = new PaintPanel();

        paintPanel.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                paintPanel.addRect(e.getX(), e.getY());
            }
        });

        frame.setLayout(new FlowLayout());

        frame.add(paintPanel);
        frame.add(new JButton("Dummy"));

        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String... args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Test();
            }
        });
    }
}

class PaintPanel extends JPanel {

    public PaintPanel() {
        addRect(100, 100);
    }
    ArrayList<Rectangle> rects = new ArrayList<>();

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setPaintMode();

        for (Rectangle r : rects) {
            g2d.setStroke(new BasicStroke(1));
            g2d.fillRect(r.x, r.y, r.width, r.height);
        }
    }

    public void addRect(int x, int y) {
        rects.add(new Rectangle(x, y, 10, 10));
        repaint();
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(300, 300);
    }
}

关于java - paintComponent 在我的绘图之上绘制其他组件，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13358658/