Java-最小化JFrame时，绘图消失了 [英] Java - Drawing dissappears when minimizing JFrame

问题描述

我正在尝试创建绘画软件，但最终出现了图形消失的问题.

I'm trying to create a paint software, but have ended up with the issue of dissappearing graphics.

我的课如下:

public class CanvasFrame extends JPanel {

    private Point lastMousePoint;
    ArrayList<Point> location = new ArrayList<Point>();


    public CanvasFrame() {


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

        addMouseMotionListener(new MouseMotionAdapter() {
            public void mouseDragged(MouseEvent e) {
                Graphics g = getGraphics();
                g.drawLine(lastMousePoint.x, lastMousePoint.y, e.getX(), e.getY());
                lastMousePoint = new Point(e.getX(), e.getY());
                g.dispose();
            }
        });
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Drawing with friends");
         frame.getContentPane().add(new CanvasFrame(), BorderLayout.CENTER);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800, 600);
        frame.setLocationRelativeTo(null);
        frame.setResizable(false);
        frame.setVisible(true);
    }
}

该软件的绘图部分运行正常，但随着问题的发生，在最小化时该绘图消失了.

The drawing portion of the software is working fine, but as the issue informs, the drawing dissappears on minimizing.

我尝试解决覆盖Graphics g的问题，以及将所有鼠标点保存在Array中，但是没有运气.到处搜寻我找不到确切项目的解决方案，所以希望大家能帮忙.

I've tried working around with overriding Graphics g, as well as saving all the mouse points in an Array, but without luck. Searching around I was unable to find a solution to my exact project, so I hope you guys can help.

推荐答案

我修复了您的代码，以便在拖动鼠标时画一条线.释放时会画一条新线，然后再次按鼠标左键.

I fixed up your code so that you draw a line as long as you're dragging the mouse. You draw a new line when you release and press the left mouse button again.

这是我对代码所做的更改.

Here are the changes I made to the code.

1. 我将JFrame代码包装在Runnable中，并通过调用SwingUtilities invokeLater方法来调用Swing GUI. invokeLater方法将创建和更新Swing GUI组件放在事件上派遣线程.我和Oracle都要求每个人都在Event Dispatch线程上启动他们的Swing应用程序.

1. I wrapped the JFrame code in a Runnable, and invoked the Swing GUI with a call to the SwingUtilities invokeLater method. The invokeLater method puts the creation and updating of the Swing GUI components on the Event Dispatch thread. Oracle and I demand that everyone starts their Swing application on the Event Dispatch thread.

我添加了paintComponent方法来绘制位置列表中的点.

I added the paintComponent method to paint the Points in the location List.

我修改了鼠标方法，以将点添加到位置列表中.

I modified the mouse methods to add points to the location List.

我将大小信息从JFrame移到了JPanel.我们不在乎JFrame的大小.我们确实关心绘图面板的尺寸.

I moved the size information from the JFrame to the JPanel. We don't care about the size of the JFrame. We do care about the size of the drawing panel.

代码如下:

package com.ggl.testing;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class CanvasFrame extends JPanel {

    private static final long serialVersionUID = -2454929744982913302L;

    private List<Point> location = new ArrayList<Point>();

    public CanvasFrame() {
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                location.clear();
                location.add(e.getPoint());
            }
        });

        addMouseMotionListener(new MouseMotionAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                location.add(e.getPoint());
                repaint();
            }
        });

        setPreferredSize(new Dimension(800, 600));
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        if (location.size() <= 0) {
            return;
        }

        Point p = location.get(0);
        for (int i = 1; i < location.size(); i++) {
            Point q = location.get(i);
            g.drawLine(p.x, p.y, q.x, q.y);
            p = q;
        }
    }

    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame("Drawing with friends");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new CanvasFrame(), BorderLayout.CENTER);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        };
        SwingUtilities.invokeLater(runnable);
    }
}

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