Netbeans：無法在Swing編輯器中添加自定義JPanel

Question

我在將Netbeans Swing編輯器中的JFrame添加到自定義JPanel時遇到了問題。

爲了排除其他問題，我做了一個全新的JFrame，並嘗試拖動我的JPanel（JPanel甚至在同一個包中）。它彈出一個錯誤信息：

警告：無法加載組件類GUI（nameofpanel）從項目 ...（路徑）...類找不到。請注意，該類必須編譯爲 ，並且必須是目標GUI窗體所屬的 項目的源或依賴項的一部分。

我已經成功地將JPanels添加到框架之前使用此方法，但現在它阻止我這樣做。我在Netbeans的7.1和7.3版本中遇到了同樣的錯誤。

我想我可能需要構建JPanel類文件，但是這樣做的選項是灰顯的。我甚至嘗試過一次清潔並且沒有任何效果。

這裏是我的JFrame：

/* 
* To change this template, choose Tools | Templates 
* and open the template in the editor. 
*/ 
package gui; 

/** 
* 
* @author chris 
*/ 
public class MainFrame extends javax.swing.JFrame { 

    /** 
    * Creates new form MainFrame 
    */ 
    public MainFrame() { 
     initComponents(); 
    } 

    /** 
    * This method is called from within the constructor to initialize the form. 
    * WARNING: Do NOT modify this code. The content of this method is always 
    * regenerated by the Form Editor. 
    */ 
    @SuppressWarnings("unchecked") 
    // <editor-fold defaultstate="collapsed" desc="Generated Code">       
    private void initComponents() { 

     setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); 

     javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); 
     getContentPane().setLayout(layout); 
     layout.setHorizontalGroup(
      layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGap(0, 400, Short.MAX_VALUE) 
     ); 
     layout.setVerticalGroup(
      layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGap(0, 300, Short.MAX_VALUE) 
     ); 

     pack(); 
    }// </editor-fold>       

    /** 
    * @param args the command line arguments 
    */ 
    public static void main(String args[]) { 
     /* Set the Nimbus look and feel */ 
     //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) "> 
     /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel. 
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */ 
     try { 
      for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) { 
       if ("Nimbus".equals(info.getName())) { 
        javax.swing.UIManager.setLookAndFeel(info.getClassName()); 
        break; 
       } 
      } 
     } catch (ClassNotFoundException ex) { 
      java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } catch (InstantiationException ex) { 
      java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } catch (IllegalAccessException ex) { 
      java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } catch (javax.swing.UnsupportedLookAndFeelException ex) { 
      java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } 
     //</editor-fold> 

     /* Create and display the form */ 
     java.awt.EventQueue.invokeLater(new Runnable() { 
      public void run() { 
       new MainFrame().setVisible(true); 
      } 
     }); 
    } 
    // Variables declaration - do not modify      
    // End of variables declaration     
} 

而且我的JPanel：

package GUI; 


import java.awt.Image; 
import java.io.*; 
import javax.imageio.*; 
import javax.swing.*; 

/* 
* Represents one card graphically /** 
* 
* @author Student-HSLH133 
*/ 
public class CardPanel extends javax.swing.JPanel { 

    private Image cardImage; 

    /** 
    * Creates new form CardPanel 
    */ 
    public CardPanel() { 
     initComponents(); 
     //Set to face down card initially 
     //Hey look, some Lisp code, jk 
     try { 
      cardLabel.setIcon(imageToIcon(ImageIO.read(new File("images/gbCard52.gif")))); 
     } 
     catch (Exception e){ 
      System.out.println("Failed to load the image."); 
      System.exit(-1); 
     } 
    } 

    public void setCard(Image img) { 
     cardLabel.setIcon(imageToIcon(img)); 
     repaint(); 
    } 

// -------------- end of load_picture --------------------------- 
    private ImageIcon imageToIcon(Image img) { 
     return new ImageIcon(img); 
    } 

    /** 
    * This method is called from within the constructor to initialize the form. 
    * WARNING: Do NOT modify this code. The content of this method is always 
    * regenerated by the Form Editor. 
    */ 
    @SuppressWarnings("unchecked") 
    // <editor-fold defaultstate="collapsed" desc="Generated Code">       
    private void initComponents() { 

     cardLabel = new javax.swing.JLabel(); 

     setMaximumSize(new java.awt.Dimension(72, 102)); 
     setMinimumSize(new java.awt.Dimension(72, 102)); 
     setPreferredSize(new java.awt.Dimension(72, 102)); 
     setLayout(new java.awt.BorderLayout()); 

     cardLabel.setMaximumSize(new java.awt.Dimension(72, 102)); 
     cardLabel.setMinimumSize(new java.awt.Dimension(72, 102)); 
     cardLabel.setPreferredSize(new java.awt.Dimension(72, 102)); 
     add(cardLabel, java.awt.BorderLayout.CENTER); 
     cardLabel.getAccessibleContext().setAccessibleName("card"); 
    }// </editor-fold>       
    // Variables declaration - do not modify      
    private javax.swing.JLabel cardLabel; 
    // End of variables declaration     
} 

我完全失去了。到底是怎麼回事？

編輯：我以某種方式得到它編譯JPanel，但我仍然得到同樣的錯誤。認爲它可能是JPanel本身的東西，我做了一個新的自定義JPanel，編譯它，並試圖添加它，它工作。

編輯2：我已經試過評論我在JPanel類中完成的自定義內容，但無濟於事。

Answer 1

我從來沒有做過這件事，但我認爲這與錯誤的文件跟蹤有關，或者是關於我的JPanel類文件損壞的東西。

將方法和變量移動到新的JPanel類似乎工作正常，所以這是解決方法。