repaint()不调用PaintComponent以使用Graphics2D [英] repaint() not calling PaintComponent to use Graphics2D
问题描述
我花了几天时间试图让Graphics2D类在我的代码中工作.我以这样的方式构造它:注册了click事件时，完成了对重画的调用，但是，只有在到达调用repaint()的阶段时，才会产生nullpointer异常.
I have spent a few days now trying to get the Graphics2D class to work within my code. I have it structured in such a way that when a click event is registered the call to repaint is done, however this only produces a nullpointer exception when it reaches the stage of calling repaint().
在调试时一切都按预期方式工作，而不是从paintComponent方法中调用，但是尝试使用paintComponent和repaint()正确调用代码以允许Graphics2D类显示到每个点的线时，这一切均不起作用
It is all working as expected when debugging and not called from within the paintComponent method, however when trying to call the code properly using paintComponent and repaint() to allow the Graphics2D class to display the lines to each point, It's not working.
我已将我的代码部分包括在内，但我上班时遇到了困难.任何帮助将不胜感激.预先谢谢你.
I have included the parts of my code that I am having difficulty getting to work. Any help whatsoever will really be appreciated. Thank you in advance.
下面是包含我的mouseListener的GUI类.
Below is the GUI class that incldes my mouseListener.
public class GUI extends JPanel implements MouseListener {
private JLabel label;
public BufferedImage getImg() {
return img;
}
public void mouseClicked(java.awt.event.MouseEvent e) {
// TODO Auto-generated method stub
label = new JLabel();
//set point equal to the location of the mouse click on the image label
Point b = e.getPoint();
//place we are going to print the dots
segmentation.x = b.x; //gets the x coordinate
segmentation.y = b.y; //gets the y coordinate
System.out.println("x = " + segmentation.x);
System.out.println("y = " + segmentation.y);
//set the global img in the segmentation class equal to that of the one in the current tab
segmentation.setImg(tabbedPane.getSelectedIndex(), getImg());
segmentation.paintUpdate();
label = segmentation.getLabel();
//if i run this line of code the existing label I already have with simply vanish because of the paintComponent method not being called upon properly.
//tabbedPane.setComponentAt(tabbedPane.getSelectedIndex(), label);
}
这是细分类，其中包含我无法正确调用的paintComponent方法.
This is the Segmentation class that includes the paintComponent method that I am having trouble calling upon properly.
public class Segmentation extends JLabel {
public int[] xpoints = new int[50];
public int[] ypoints = new int[50];
private int npoints = 0;
public int x;
public int y;
GeneralPath polyline;
Graphics2D g2;
JLabel label;
BufferedImage img;
ImageIcon icon;
public void paintUpdate() {
repaint();
}
public void setImg(int tabNum, BufferedImage img) {
this.img = img;
}
public GeneralPath createPath() {
// if (npoints > 0) {
polyline.moveTo(xpoints[0], ypoints[0]);
for(int i = 1; i < xpoints.length; i++) {
//add the position of the point to the respective x and y arrays
polyline.lineTo(xpoints[i], ypoints[i]);
}
// }
return polyline;
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
System.out.println("we're in the paint component method");
//set up for the new jlabel
label = new JLabel();
label.setIcon(new javax.swing.ImageIcon(img));
label.setHorizontalAlignment(JLabel.LEFT);
label.setVerticalAlignment(JLabel.TOP);
//add the position of the point to the respective x and y arrays
xpoints[npoints] = x;
ypoints[npoints] = y;
if (npoints == 0) {
JOptionPane.showMessageDialog(null, "Your first point has been added successfully");
}
else {
JOptionPane.showMessageDialog(null, "Your " + npoints + " rd/th" + " point has been added successfully");
}
polyline = createPath();
// Draws the buffered image to the screen.
g2.drawImage(img, 0, 0, this);
g2.draw(polyline);
npoints++;
}
推荐答案
您的Segmentation类有两个JLabel，一个是该类本身的对象，它具有paintComponent重写，并且很可能从未使用过:
Your Segmentation class has two JLabels, one the object of the class itself, which has a paintComponent override and is likely never used:
public class Segmentation extends JLabel {
和另一个称为Label的JLabel，它由类中的成分保存，而该类实际上没有使用方法重写，并且似乎在遮盖"该类的实例:
and the other a JLabel called label which is held by composition in the class which doesn't have the method override which is in fact used and appears to be "shadowing" the class's instance:
JLabel label
如果要调用paintComponent，则需要使用实际上覆盖该方法的label对象.
If you want paintComponent to be called, you'll need to use the label object that in fact overrides that method.
同样，您似乎正在paintComponent(...)方法(??)中创建组件.永远不要这样做，也不要在此方法中包含程序逻辑.
Also you appear to be creating components within the paintComponent(...) method (??). Never do that nor have program logic within this method.
要绘制图像，我通常会覆盖paintComponent并使用其Graphics/Graphics2D对象进行绘制.例如:
To draw on an image, I usually override paintComponent and draw with its Graphics/Graphics2D object. For example:
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import javax.imageio.ImageIO;
import javax.swing.*;
public class DrawOnLabel extends JLabel {
public static final String GIRAFFE_IMG_URL = "http://upload.wikimedia.org/wikipedia/commons/thumb" +
"/9/9e/Giraffe_Mikumi_National_Park.jpg/474px-Giraffe_Mikumi_National_Park.jpg";
private static final Color LINES_COLOR = Color.red;
private static final Color CURRENT_LINE_COLOR = new Color(255, 200, 200);
private List<Line2D> lineList = new ArrayList<Line2D>();
private Line2D currentLine = null;
public DrawOnLabel() throws IOException {
URL giraffeUrl = new URL(GIRAFFE_IMG_URL);
BufferedImage img = ImageIO.read(giraffeUrl);
ImageIcon icon = new ImageIcon(img);
setIcon(icon);
MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
addMouseListener(myMouseAdapter);
addMouseMotionListener(myMouseAdapter);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.setColor(LINES_COLOR);
for (Line2D line : lineList) {
g2.draw(line);
}
if (currentLine != null) {
g2.setColor(CURRENT_LINE_COLOR);
g2.draw(currentLine);
}
}
private class MyMouseAdapter extends MouseAdapter {
Point p1 = null;
@Override
public void mousePressed(MouseEvent e) {
p1 = e.getPoint();
}
@Override
public void mouseReleased(MouseEvent e) {
if (currentLine != null) {
currentLine = new Line2D.Double(p1, e.getPoint());
lineList.add(currentLine);
currentLine = null;
p1 = null;
repaint();
}
}
@Override
public void mouseDragged(MouseEvent e) {
if (p1 != null) {
currentLine = new Line2D.Double(p1, e.getPoint());
repaint();
}
}
}
private static void createAndShowGui() {
DrawOnLabel mainPanel = null;
try {
mainPanel = new DrawOnLabel();
} catch (IOException e) {
e.printStackTrace();
System.exit(-1);
}
JFrame frame = new JFrame("DrawOnLabel");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.setResizable(false);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
这篇关于repaint()不调用PaintComponent以使用Graphics2D的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
