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java - 无法从扩展的 JPanel 类中看到 ImageIcon

问题描述

我有一个扩展 JPanel 的类，我希望它显示一个 ImageIcon。有些事情似乎没有通过。找到 map.png 并且当我在类中打印出它的大小时是正确的。另外，我将面板设置为黑色，所以我知道面板可以工作，但 ImageIcon 不能。

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

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
    }
}

图形用户界面.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
        

    }

}

标签： javaswingawt

解决方案

this.setLayout(null);我通过在TestPanel类中删除来修复代码。

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