调整窗口大小时，组件移动到原始位置

Question

我有一个可拖动的JPanel，它使用NetBeans IDE JFrame表单编辑器添加到JFrame中。当我运行程序并将卡片拖放到原始位置以外的位置并调整JFrame的大小时，JPanel会返回到其原始位置。

之前（当程序第一次运行）：

被移动的卡：

大小的窗口：

我毫不理解为什么会发生这种情况，以及如何预防这种情况。

我的框架：

package cards; 

import cards.cards.*; 
/** 
* 
* @author Nicki 
*/ 
public class ImgTest extends javax.swing.JFrame { 

    /** 
    * Creates new form ImgTest 
    */ 
    public ImgTest() { 
     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() { 

     card2 = new cards.cards.Card(); 

     setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); 
     setTitle("Imgtest"); 
     setMinimumSize(new java.awt.Dimension(250, 250)); 
     setPreferredSize(new java.awt.Dimension(250, 250)); 

     javax.swing.GroupLayout card2Layout = new javax.swing.GroupLayout(card2); 
     card2.setLayout(card2Layout); 
     card2Layout.setHorizontalGroup(
      card2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGap(0, 71, Short.MAX_VALUE) 
     ); 
     card2Layout.setVerticalGroup(
      card2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGap(0, 96, Short.MAX_VALUE) 
     ); 

     javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); 
     getContentPane().setLayout(layout); 
     layout.setHorizontalGroup(
      layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGroup(layout.createSequentialGroup() 
       .addGap(21, 21, 21) 
       .addComponent(card2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addContainerGap(158, Short.MAX_VALUE)) 
     ); 
     layout.setVerticalGroup(
      layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGroup(layout.createSequentialGroup() 
       .addGap(21, 21, 21) 
       .addComponent(card2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addContainerGap(133, 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(ImgTest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } catch (InstantiationException ex) { 
      java.util.logging.Logger.getLogger(ImgTest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } catch (IllegalAccessException ex) { 
      java.util.logging.Logger.getLogger(ImgTest.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } catch (javax.swing.UnsupportedLookAndFeelException ex) { 
      java.util.logging.Logger.getLogger(ImgTest.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 ImgTest().setVisible(true); 
      } 
     }); 
    } 

    // Variables declaration - do not modify      
    private cards.cards.Card card2; 
    // End of variables declaration     
} 

我的卡板：

package cards.cards; 

import cards.images.CardImageProvider; 
import java.awt.Canvas; 
import java.awt.Cursor; 
import java.awt.Graphics; 
import java.awt.Image; 
import java.awt.event.MouseAdapter; 
import java.awt.event.MouseEvent; 
import java.awt.event.MouseMotionAdapter; 
import javax.swing.JPanel; 

/** 
* 
* @author Nicki 
*/ 
public class Card extends JPanel { 

    private Image cardImg; 
    private Cards card; 
    private volatile int draggedAtX, draggedAtY; 


    public Card(Cards c) { 
     this.setSize(71, 96); 
     card = c; 
     cardImg = CardImageProvider.getCardImage(c); 
     addMouseListener(new MouseAdapter(){ 

      public void mousePressed(MouseEvent e){ 
       draggedAtX = e.getX(); 
       draggedAtY = e.getY(); 
      } 
     }); 

     addMouseMotionListener(new MouseMotionAdapter(){ 
      public void mouseDragged(MouseEvent e){ 
       setLocation(e.getX() - draggedAtX + getLocation().x, 
         e.getY() - draggedAtY + getLocation().y); 
       repaint(); 
      } 
     }); 
     this.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR)); 
    } 

    public Card(){ 
     this(Unknown.UNKNOWN); 
    } 

    @Override 
    public void paintComponent(Graphics g) { 
     this.setSize(71, 96); 
     g.drawImage(cardImg, 0, 0, this); 
    } 

    public void setCard(Cards c) { 
     card = c; 
     cardImg = CardImageProvider.getCardImage(c); 
     repaint(); 
    } 

    public Cards getCard() { 
     return card; 
    } 


} 

我想知道如何防止卡移动回其第一位置。 在此先感谢。

Answer 1

默认情况下，IDE将使用布局管理器来定位框架上的组件。

当您拖动面板时，您将手动设置面板的位置并覆盖由布局管理器确定的位置。

但是，当您调整框架大小时，将再次执行布局管理器代码，并将面板恢复到原始位置。

您需要更改代码，以便拖动的面板的父面板使用“空布局”。但是，当你这样做时，你现在负责设置面板的大小和位置。