无法从扩展的 JPanel 类中看到图像图标

Question

我有一个扩展JPanel的类，我希望它显示一个ImageIcon。有些事情似乎没有解决。找到了map.png，当我在类中打印出它的大小时，它是正确的。此外，我把面板变成了黑色，这样我就知道面板可以工作，但ImageIcon不行。

然而，当我将TestPanel.java中的相同代码放入GUI.java的构造函数中时，ImageIcon就可以工作了。

有人能告诉我为什么ImageIcon在TestPanel.java中不起作用，但在GUI.java中起作用吗？

这是我的代码

测试面板.java

public class TestPanel extends JPanel {

public static JLabel map = new JLabel();
public TestPanel() {
this.setLayout(null); //to prevent icon from taking the whole screen
this.setVisible(true); //make frame visible
this.setBounds(0, 0, 100, 100);

this.setBackground(new Color(0,0,0));

Image imageToScale = new ImageIcon("map.png").getImage();
double scale = .9; //scale
int x = (int) (imageToScale.getWidth(null) * scale); //leave image observer as null because we know that the image is loaded
int y = (int) (imageToScale.getHeight(null) * scale);
Image scaledImage = imageToScale.getScaledInstance( x, y, java.awt.Image.SCALE_SMOOTH); //scale the image
ImageIcon image = new ImageIcon(scaledImage); //case the image into an image icon

this.setBounds(0, -4, image.getIconWidth(), image.getIconHeight()); //set position and size of panel to the size of the image. -4 on the Y position because it was not aligned with the top

map.setIcon(image); //set icon for map label
this.add(map); //add label to panel
}
}

GUI.java

public class GUI extends JFrame {

public static JPanel problemPanel = new JPanel(); //panel where the points and path will be displayed
public static JLabel map = new JLabel();

public static TestPanel test = new TestPanel();

public GUI() {
this.setLayout(null); //to prevent icon from taking the whole screen

this.add(test);

//Frame
this.setVisible(true); //make frame visible
this.setSize(1200,1000); //set frame size
this.setTitle("Travelling Apache Pizza Delivery Driver Problem (TAPDDP)"); //set title of panel
this.setDefaultCloseOperation(this.EXIT_ON_CLOSE); //terminates program when frame is closed
this.setLocationRelativeTo(null); //open frame in the middle of the screen
this.setResizable(false); //prevent resizing of GUI

}
}

Answer 1

我通过删除TestPanel类中的this.setLayout(null);修复了代码。