在过去的两天里,我试图了解

Java如何处理图形,但是在这方面却失败了.我的主要问题是如何以及何时应该调用paint()(或更新的paintComponent()).

在下面的代码中我看到了什么时候创建的东西,paintComponent()永远不会被调用,除非我自己手动添加一个调用或者调用JFrame.paintAll()/ JFrame.paintComponents().

我将paint()方法重命名为paintComponent(),希望能解决我永远不会被调用的问题(即使在repaint()),但没有运气.

package jpanelpaint;

import java.awt.*;

import javax.imageio.*;

import javax.swing.*;

import java.io.*;

import java.util.ArrayList;

public class ImageLoadTest extends JComponent {

ArrayList list;

public ImageLoadTest() {

list = new ArrayList();

try { //create the images (a deck of 4 cards)

for(String name : createImageFileNames(4)){

System.err.println(name);

list.add(ImageIO.read(new File(name)));

}

} catch (IOException e) { }

}

protected void paintComponent(Graphics g) {

int yOffset=0;

System.err.println("ImageLoadTest.paintComponent()");

for(Image img : list) {

g.drawImage(img, 0, yOffset, null);

yOffset+=20;

}

}

public static void main(String args[]) throws InterruptedException {

JFrame frame = new JFrame("Empty JFrame");

frame.setSize(new Dimension(1000, 500));

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setVisible(true);

Thread.sleep(1000);

frame.setTitle("Loading images");

ImageLoadTest ilt = new ImageLoadTest();

frame.add(ilt);

//update the screen

//DOESN'T WORK. only works if I call frame.paintAll(frame.getGraphics())

ilt.repaint();

frame.repaint();

Thread.sleep(1000);

frame.setTitle("Setting background");

ilt.setBackground(Color.BLACK);

//update the screen - DOESN'T WORK even if I call paintAll ..

ilt.repaint();

frame.repaint();

//have to call one of these to get anything to display

// ilt.paintComponent(frame.getGraphics()); //works

frame.paintComponents(frame.getGraphics()); //works

}

//PRIVATE HELPER FUNCTIONS

private String[] createImageFileNames(int count){

String[] fileNames = new String[count];

for(int i=0; i < count; i++)

fileNames[i] = "Cards" + File.separator + (i+1) + ".bmp";

return fileNames;

}

}