JFrame中的BufferedImage不显示 [英] BufferedImage in JFrame doesnt Show up
问题描述
试图将图像打印到窗口中。一切运行都没有错误，并且如果将drawImage替换为另一个图形类，它也可以正常工作。但是，窗口缺少图像，我不确定为什么。同样，JFrame素材和图形可以与绘制其他图形一起正常工作，但不能在此处绘制图像。
trying to get an image to print into a window. Everything runs without errors, and it also works if I replace the drawImage with another graphics class. However, the window is missing the image, and i'm not sure why. Again, the JFrame stuff and Graphics work fine with drawing other graphics, but only doesn't draw the image here. Thanks.
import javax.swing.JApplet;
import javax.swing.JFrame;
import javax.imageio.*;
import javax.imageio.stream.*;
import java.awt.*;
import java.awt.image.*;
import java.io.*;
public class GraphicsMovement2 extends JApplet{
BufferedImage image = null;
public static void main(String args[]){
BufferedImage image = null;
try {
File file = new File("C:\\Users/Jonheel/Google Drive/School/10th Grade/AP Computer Science/Junkbin/MegaLogo.png");
ImageInputStream imgInpt = new FileImageInputStream(file);
image = ImageIO.read(file);
}
catch(FileNotFoundException e) {
System.out.println("x");
}
catch(IOException e) {
System.out.println("y");
}
JApplet example = new GraphicsMovement2();
JFrame frame = new JFrame("Movement");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(example);
frame.setSize(new Dimension(1366,768)); //Sets the dimensions of panel to appear when run
frame.setVisible(true);
}
public void paint (Graphics page){
page.drawImage(image, 100, 100, 100, 100, Color.RED, this);
}
}
推荐答案
您已经两次定义了 image ...
You've defined image twice...
BufferedImage image = null;
public static void main(String args[]){
BufferedImage image = null;
这实际上意味着您到达绘画方法，它是 null ，因为您尚未初始化实例变量。
This essentially means that by the time you get to the paint method, it is null as you haven't initialized the instance variable.
另一个问题是您将尝试从静态引用加载图像，但图像没有声明为 static 。最好将此逻辑移到构造函数或实例方法中。
Another problem you will have is the fact that you are trying to load the image from a static reference but the image isn't declared as static. Better to move this logic into the constructor or instance method.
在您使用容器时不要使用 JApplet 作为容器要添加到 JFrame 中，最好使用 JPanel 之类的东西。
Don't use JApplet as your container when you're adding to a JFrame, you're better of using something like JPanel. It will help when it comes to adding things to the container.
您必须打电话 super.paint（g） ...实际上，不要覆盖诸如 JApplet 。使用类似 JPanel 的方法，并覆盖 paintComponent 方法。
YOU MUST CALL super.paint(g)...in fact, DON'T override the paint method of top level containers like JFrame or JApplet. Use something like JPanel and override the paintComponent method instead. Top level containers aren't double buffered.
paint 方法完成了许多重要的工作，并且更加容易使用 JComponent＃paintComponent ...但不要忘记调用 super.paintComponent
The paint methods does a lot of important work and it's just easier to use JComponent#paintComponent ... but don't forget to call super.paintComponent
已更新
您需要定义图片
因为您将 image 声明为<$的实例字段，所以c $ c> GraphicsMovement2 ，则需要引用 GraphicsMovement2 的实例才能引用它。
Because you declared the image as an instance field of GraphicsMovement2, you will require an instance of GraphicsMovement2 in order to reference it.
但是，在您的 main 方法（即静态）中，您还声明了一个名为<$ c的变量。 $ c>图片。
However, in you main method, which is static, you also declared a variable named image.
的看不到您在绘画方法GraphicsMovement2 main 中声明的变量，只能看到实例字段（ null ）。
The paint method of GraphicsMovement2 can't see the variable you declared in main, only the instance field (which is null).
要解决此问题，您需要将图像的加载移动到 GraphicsMovement2 的实例的上下文中，这可以最好地实现（在您的上下文中），但是将图像的加载移动到<$的构造函数中c $ c> GraphicsMovement2
In order to fix the problem, you need to move the loading of the image into the context of a instance of GraphicsMovement2, this can be best achived (in your context), but moving the image loading into the constructor of GraphicsMovement2
public GraphicsMovement2() {
try {
File file = new File("C:\\Users/Jonheel/Google Drive/School/10th Grade/AP Computer Science/Junkbin/MegaLogo.png");
ImageInputStream imgInpt = new FileImageInputStream(file);
image = ImageIO.read(file);
}
catch(FileNotFoundException e) {
System.out.println("x");
}
catch(IOException e) {
System.out.println("y");
}
}
下面的两个示例将产生相同的结果。
The two examples below will produce the same result...
简单方法
public class TestPaintImage {
public static void main(String[] args) {
new TestPaintImage();
}
public TestPaintImage() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException ex) {
} catch (InstantiationException ex) {
} catch (IllegalAccessException ex) {
} catch (UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new ImagePane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class ImagePane extends JPanel {
public ImagePane() {
setLayout(new BorderLayout());
ImageIcon icon = null;
try {
icon = new ImageIcon(ImageIO.read(new File("/path/to/your/image")));
} catch (Exception e) {
e.printStackTrace();
}
add(new JLabel(icon));
}
}
}
硬方法
public class TestPaintImage {
public static void main(String[] args) {
new TestPaintImage();
}
public TestPaintImage() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException ex) {
} catch (InstantiationException ex) {
} catch (IllegalAccessException ex) {
} catch (UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new ImagePane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class ImagePane extends JPanel {
private BufferedImage background;
public ImagePane() {
try {
background = ImageIO.read(new File("/path/to/your/image"));
} catch (Exception e) {
e.printStackTrace();
}
}
@Override
public Dimension getPreferredSize() {
return background == null ? super.getPreferredSize() : new Dimension(background.getWidth(), background.getHeight());
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (background != null) {
int x = (getWidth() - background.getWidth()) / 2;
int y = (getHeight() - background.getHeight()) / 2;
g.drawImage(background, x, y, this);
}
}
}
}
阅读教程的时间
- Creating a GUI With JFC/Swing
- Performing Custom Painting
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