我试图在Java中的Canvas中绘制两行,分别调用两个方法,但是当我绘制第二行时,第一行消失(Java清除屏幕).我怎么能避免这种情况？我想看两条线.我已经看过油漆教程(如何制作像Windows上的Paint这样的程序)用户使用鼠标绘制线条,当绘制一条线时,另一条线不会消失.他们只是调用paint方法,它不会清除屏幕.

如果有人能帮助我,我将不胜感激.

谢谢.

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import java.awt.BorderLayout;

import java.awt.Canvas;

import java.awt.Color;

import java.awt.Graphics;

import javax.swing.JFrame;

public class CircuitTracePlotView extends JFrame {

private CircuitTracePlot circuitTracePlot;

public CircuitTracePlotView() {

this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

this.getContentPane().add(circuitTracePlot = new CircuitTracePlot(), BorderLayout.CENTER);

this.pack();

this.setSize(250,250);

this.setLocationRelativeTo(null);

this.setVisible(true);

circuitTracePlot.drawLine();

circuitTracePlot.drawOval();

}

}

class CircuitTracePlot extends Canvas {

private final static short LINE = 1;

private final static short OVAL = 2;

private int paintType;

private int x1;

private int y1;

private int x2;

private int y2;

public CircuitTracePlot() {

this.setSize(250,250);

this.setBackground(Color.WHITE);

}

private void setPaintType(int paintType) {

this.paintType = paintType;

}

private int getPaintType() {

return this.paintType;

}

public void drawLine() {

this.setPaintType(LINE);

this.paint(this.getGraphics());

}

public void drawOval() {

this.setPaintType(OVAL);

this.paint(this.getGraphics());

}

public void repaint() {

this.update(this.getGraphics());

}

public void update(Graphics g) {

this.paint(g);

}

public void paint(Graphics g) {

switch (paintType) {

case LINE:

this.getGraphics().drawLine(10, 10, 30, 30);

case OVAL:

this.getGraphics().drawLine(10, 20, 30, 30);

}

}

}

主要课程

import javax.swing.SwingUtilities;

import view.CircuitTracePlotView;

public class Main {

public static void main(String[] args) {

SwingUtilities.invokeLater(new Runnable() {

public void run() {

CircuitTracePlotView cr = new CircuitTracePlotView();

}

});

}

}

解决方法:

>你几乎不应该直接调用paint(…).我可以算一下我需要做的时间.

>不要通过在组件上调用getGraphics()来获取Graphics对象,因为它将返回非持久的Graphics对象.而是绘制BufferedImage并在paint方法中显示或在paint方法中绘制(如果是AWT).

>由于这是一个Swing GUI,因此不要使用AWT组件进行绘制.使用JPanel并覆盖paintComponent(…)方法,而不是paint(…)方法.否则你将失去Swing图形的所有好处,包括自动双缓冲.

>应该在paintComponent(Graphics g)覆盖中调用super.paintComponent(g)方法,通常作为此方法内部的第一个方法调用.这使组件可以自己进行管家绘画,包括擦除需要擦除的绘图.

>阅读有关Swing图形的教程,因为大部分内容都在那里得到了很好的解释.例如,请看这里：

编辑

>为了保持图像的持久性,我建议您绘制一个BufferedImage,然后在JPanel的paintComponent(…)方法中显示该图像.

>或者另一种选择是创建一个Shape对象集合,可能是一个ArrayList< Shape>并使用您想要绘制的Shapes填充它,然后在paintComponent(…)方法中将Graphics对象强制转换为Graphics2D对象并遍历Shape集合,使用g2d.draw(shape)绘制每个形状重复.

自Trash发布他的代码,…

import java.awt.Dimension;

import java.awt.Graphics;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.*;

public class CircuitTracePlot2 extends JPanel {

private static final int PREF_W = 250;

private static final int PREF_H = PREF_W;

private int drawWidth = 160;

private int drawHeight = drawWidth;

private int drawX = 10;

private int drawY = 10;

private PaintType paintType = PaintType.LINE;

public CircuitTracePlot2() {

}

@Override

public Dimension getPreferredSize() {

return new Dimension(PREF_W, PREF_H);

}

public void setPaintType(PaintType paintType) {

this.paintType = paintType;

repaint();

}

@Override

protected void paintComponent(Graphics g) {

super.paintComponent(g);

if (paintType == null) {

return;

}

switch (paintType) {

case LINE:

g.drawLine(drawX, drawY, drawWidth, drawHeight);

break;

case OVAL:

g.drawOval(drawX, drawY, drawWidth, drawHeight);

break;

case SQUARE:

g.drawRect(drawX, drawY, drawWidth, drawHeight);

default:

break;

}

}

private static void createAndShowGui() {

final CircuitTracePlot2 circuitTracePlot = new CircuitTracePlot2();

JFrame frame = new JFrame("CircuitTracePlot2");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.getContentPane().add(circuitTracePlot);

frame.pack();

frame.setLocationByPlatform(true);

frame.setVisible(true);

int timerDelay = 2 * 1000;

new Timer(timerDelay , new ActionListener() {

private int paintTypeIndex = 0;

@Override

public void actionPerformed(ActionEvent arg0) {

paintTypeIndex++;

paintTypeIndex %= PaintType.values().length;

circuitTracePlot.setPaintType(PaintType.values()[paintTypeIndex]);

}

}).start();

}

public static void main(String[] args) {

SwingUtilities.invokeLater(new Runnable() {

public void run() {

createAndShowGui();

}

});

}

}

enum PaintType {

LINE, OVAL, SQUARE;

}

标签：java,screen,clear,paint,java-canvas

来源： https://codeday.me/bug/20190529/1178821.html