最小化时窗口的内容消失 [英] Window's content disappears when minimized
问题描述
我有一个简单的类，它在鼠标拖动时画一条线，在鼠标按下(释放)时画点.
I have a simple class that draws a line when mouse dragging or a dot when mouse pressing(releasing).
当我最小化应用程序然后还原它时，窗口的内容消失了，最后一个点(像素)除外.我了解每次窗口更改时，方法super.paint(g)都会重新绘制背景，但是无论是否使用它，结果似乎都是相同的.两者之间的区别在于，当我不使用它时，在窗口上绘制的像素多于一个像素，但并不是我的全部绘画.我该如何解决?
When I minimize the application and then restore it, the content of the window disappears except the last dot (pixel). I understand that the method super.paint(g) repaints the background every time the window changes, but the result seems to be the same whether I use it or not. The difference between the two of them is that when I don't use it there's more than a pixel painted on the window, but not all my painting. How can I fix this?
这是课程.
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);
}
}
推荐答案
不是这意味着我每次按下或拖动鼠标时都会绘制所有点(而不是一个点)吗?
Doesn't that mean I will draw all the points(instead of one) everytime I press or drag the mouse?
是的，但是@Dave的方法对于数千个节点而言完全令人满意，如 GraphPanel .除此之外，请考虑 flyweight模式 ，如 JTable渲染器，并说明了
Yes, but @Dave's approach is perfectly satisfactory for thousands of nodes, as may be seen in GraphPanel. Beyond that, consider the flyweight pattern, as used by JTable renderers and illustrated here.
附录:关注您的 AWTPainting 问题，以下变化可能说明
Addendum: Focusing on your AWTPainting questions, the variation below may illustrate the difference between System- and App-triggered Painting. As the mouse is dragged, repaint() invokes update(), which calls paint(); this is app-triggered. As you resize the window, only paint() is called (no red numbers are drawn); this is system-triggered. Note that there is a flicker when the mouse is released after resizing.
通常在清除并重绘整个组件的背景后才会发生闪烁:
Flickering typically occurs when the entire component's background is cleared and redrawn:
4.如果该组件没有没有覆盖
update()，则默认实现update()会清除该组件的背景(如果它不是轻量级组件)，并只需调用paint().
4. If the component did not override
update(), the default implementation ofupdate()clears the component's background (if it's not a lightweight component) and simply callspaint().
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;
}
}
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