窗口最小化时内容消失

问题描述 投票：6回答：4

我有一个简单的类，当鼠标拖动时画一条线，或者当鼠标按下（释放）时画一个点。

当我将应用程序最小化，然后将其还原时，除了最后一个点（像素）外，窗口的内容都消失了。我理解的方法是 super.paint(g) 每次窗口变化时都会重新绘制背景，但无论我用不用它，结果似乎都是一样的。他们两个的区别是，当我不用它时，窗口上画的像素不止一个，但不是我画的全部。如何才能解决这个问题呢？

这里是类。

package painting;

import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import javax.swing.JFrame;
import javax.swing.JPanel;

class CustomCanvas extends Canvas{   
    Point oldLocation= new Point(10, 10);
    Point location= new Point(10, 10);
    Dimension dimension = new Dimension(2, 2);     
    CustomCanvas(Dimension dimension){  
        this.dimension = dimension;   
        this.init();
        addListeners();
    }    
    private void init(){                     
        oldLocation= new Point(0, 0);
        location= new Point(0, 0);
    }
    public void paintLine(){
        if ((location.x!=oldLocation.x) || (location.y!=oldLocation.y)) {         
            repaint(location.x,location.y,1,1);                                   
        } 
    }
    private void addListeners(){
        addMouseListener(new MouseAdapter(){
            @Override
            public void mousePressed(MouseEvent me){                   
                oldLocation = location;
                location = new Point(me.getX(), me.getY());
                paintLine();
            }
            @Override
            public void mouseReleased(MouseEvent me){                
                oldLocation = location;
                location = new Point(me.getX(), me.getY());
                paintLine();
            }
        });
        addMouseMotionListener(new MouseMotionAdapter() {
            @Override
            public void mouseDragged(MouseEvent me){                
                oldLocation = location;
                location = new Point(me.getX(), me.getY());
                paintLine();
            }
        });
    }
    @Override
    public void paint(Graphics g){  
        super.paint(g);
        g.setColor(Color.red);       
        g.drawLine(location.x, location.y, oldLocation.x, oldLocation.y);                
    }
    @Override
    public Dimension getMinimumSize() {
        return dimension; 
    }
    @Override
    public Dimension getPreferredSize() {
        return dimension;
    }

}
class CustomFrame extends JPanel {
    JPanel displayPanel = new JPanel(new BorderLayout());
    CustomCanvas canvas = new CustomCanvas(new Dimension(200, 200));        
    public CustomFrame(String titlu) {            
        canvas.setBackground(Color.white);
        displayPanel.add(canvas, BorderLayout.CENTER);            
        this.add(displayPanel);
    }   
}
public class CustomCanvasFrame {
    public static void main(String args[]) {
        CustomFrame panel = new CustomFrame("Test Paint");
        JFrame f = new JFrame();
        f.add(panel);
        f.pack();
        SwingConsole.run(f, 700, 700);
    }
}
java swing graphics awt paint
4个回答
5
投票

你没有存储你正在绘制的点的状态。当面板重新绘制时，它只有最后绘制的点的信息。

对评论的回应。

你需要有一个点的集合，例如： ArrayList<Point> location = new ArrayList<Point>();

然后，在你的监听器中。location.add(new Point(me.getX(), me.getY()));

最后，在paintLine()中

for (Point location : locations) {
  repaint(location.x,location.y,1,1); 
}

这个集合 locations 通常被称为显示列表。大多数图形程序都使用它们。

对评论的回应。

是的，我希望如此。我只是根据你的代码抛出一个想法，给你一个出发点。几乎可以肯定的是，完全按照我所描述的那样做是一个坏主意。

5
投票

这不是意味着我每次按动或拖动鼠标时都会画出所有的点（而不是一个）吗？

是的，但是 @Dave 的方法对于成千上万的节点来说是完全令人满意的，这一点可以在 GraphPanel. 除此之外，还要考虑 蝇头小楷用的 JTable 渲染器 图文并茂 此处.

增编。注重你的 AWTPainting 的问题，下面的变化可能会说明两者之间的区别。系统和应用程序触发的绘画. 随着鼠标的拖动。repaint() 调用 update()，这就要求 paint();这是应用程序触发的。当你调整窗口大小时，只有 paint() 被调用（不画红色数字）；这是系统触发的。请注意，有 是 当调整大小后释放鼠标时，会出现闪烁。

闪动通常发生在清除整个组件的背景并重新绘制时。

 4. 如果该组件没有 不 凌驾于...之上 update()的默认实现，即 update() 清除组件的背景（如果它不是一个轻量级组件），并简单地调用 paint().

AWTPainting

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Panel;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.ArrayList;
import java.util.List;

public class AWTPainting {

    public static void main(String args[]) {
        CustomPanel panel = new CustomPanel();
        Frame f = new Frame();
        f.addWindowListener(new WindowAdapter() {

            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        f.add(panel);
        f.pack();
        f.setVisible(true);
    }
}

class CustomPanel extends Panel {

    public CustomPanel() {
        this.add(new CustomCanvas(new Dimension(320, 240)));
    }
}

class CustomCanvas extends Canvas {

    private MouseAdapter handler = new MouseHandler();
    private List<Point> locations = new ArrayList<Point>();
    private Point sentinel = new Point();
    private Dimension dimension;

    CustomCanvas(Dimension dimension) {
        this.dimension = dimension;
        this.setBackground(Color.white);
        this.addMouseListener(handler);
        this.addMouseMotionListener(handler);
        this.locations.add(sentinel);
    }

    @Override
    public void paint(Graphics g) {
        g.setColor(Color.blue);
        Point p1 = locations.get(0);
        for (Point p2 : locations.subList(1, locations.size())) {
            g.drawLine(p1.x, p1.y, p2.x, p2.y);
            p1 = p2;
        }
    }

    @Override
    public void update(Graphics g) {
        paint(g);
        g.clearRect(0, getHeight() - 24, 50, 20); // to background
        g.setColor(Color.red);
        g.drawString(String.valueOf(locations.size()), 8, getHeight() - 8);
    }

    private class MouseHandler extends MouseAdapter {

        @Override
        public void mousePressed(MouseEvent e) {
            if (locations.get(0) == sentinel) { // reference identity
                locations.set(0, new Point(e.getX(), e.getY()));
            }
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            locations.add(new Point(e.getX(), e.getY()));
            repaint();
        }
    }

    @Override
    public Dimension getPreferredSize() {
        return dimension;
    }
}
2
投票

@Andrew, @Dave, @trashgod 嗨，我做了一些研究，最后，这是我得到的。如果我说的不对，请纠正我。你不能覆盖paint()，所以每次你需要做应用触发的绘画时，你都要调用repaint().Repaint()调用update()，它的默认行为是调用paint().update()用于增量绘画；这解释了当paint()做所有工作时屏幕闪烁的原因，这实际上意味着它在每一步都在画整个图像。然而，我的问题是，如果我在update方法中添加 "lovesAdded = 0"，这意味着每次我拖动鼠标时，我都会绘制整个图像（就像在paint中一样），那么为什么它不像以前那样闪烁呢？我也读过一些关于在swift中绘制的东西，我不明白为什么update()对于swift从来不被调用。你能给我解释一下为什么吗？

import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;

class CustomCanvas extends Canvas{ 
    ArrayList<Point> locations;        
    int locationsAdded;    
    Point oldLocation;
    Point location;
    Dimension dimension;
    CustomCanvas(Dimension dimension){  
        locations = new ArrayList<>();        
        this.dimension = dimension;   
        this.init();
        addListeners();
    }    
    private void init(){                          
        oldLocation= new Point(0, 0);
        location= new Point(0, 0);
    }
    public void paintLine(Graphics g, int x){
        Point p1 = (Point)locations.get(x);
        Point p2 = (Point)locations.get(x+1);
        g.drawLine(p1.x, p1.y, p2.x, p2.y);
        locationsAdded++;
    }
    @Override
    public void paint(Graphics g){          
        locationsAdded = 0;        
        g.setColor(Color.red);                  
        for(int i = locationsAdded; i < locations.size()-1; i++){
            paintLine(g, i);
        }             
    }
    public void update(Graphics g) {        
    //locationsAdded = 0;
        for (int i = locationsAdded; i < locations.size()-1; i++) {            
            paintLine(g, i);
        }
    }
    private void addListeners(){
        addMouseMotionListener(new MouseMotionAdapter() {
            @Override
            public void mouseDragged(MouseEvent me){                                   
                oldLocation = location;
                location = new Point(me.getX(), me.getY());
                locations.add(location);
                repaint();
            }
        }); 
    }

    @Override
    public Dimension getMinimumSize() {
        return dimension; 
    }
    @Override
    public Dimension getPreferredSize() {
        return dimension;
    }
}
class CustomFrame extends Panel {
    Panel displayPanel = new Panel(new BorderLayout());
    CustomCanvas canvas = new CustomCanvas(new Dimension(700, 700));        
    public CustomFrame(String titlu) {            
        canvas.setBackground(Color.white);
        displayPanel.add(canvas, BorderLayout.CENTER);            
        this.add(displayPanel);
    }  
}
public class AWTPainting {
    public static void main(String args[]) {
        CustomFrame panel = new CustomFrame("Test Paint");
        Frame f = new Frame();
        f.add(panel);
        f.pack();        
        f.setSize(700,700);                    
        f.show();                
    }
}
0
投票

将你的布局设置为Null布局

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