我的擴展JPanel的父項爲空

Question

我有一個擴展的JPanel類，它創建一個JPanel並將其添加到其父項。 getComponents從父調用正確地示出了該面板，但是從的getParent擴展實例調用返回null.layeredPane

package testing; 

import javax.swing.JButton; 

public class ParentNullExample extends javax.swing.JFrame { 

private static Panel1 mainPanel; 
private static JButton AddButton; 

private void createAndShowGUI() { 
    //Set the look and feel. 
    initLookAndFeel(); 

    setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE); 

    AddButton = new javax.swing.JButton(); 
    AddButton.setName("AddButton"); 
    AddButton.setText("Add a Row"); 
    AddButton.addActionListener(new java.awt.event.ActionListener() { 
     @Override 
     public void actionPerformed(java.awt.event.ActionEvent evt) { 
      addRowActionPerformed(evt); 
     } 
    }); 

    Panel1 componentPanel = new Panel1(true); 
    componentPanel.setName("componentPanel"); 

    mainPanel = new testing.Panel1(false); 
    mainPanel.setName("mainPanel"); 

    mainPanel.add(componentPanel); 
    mainPanel.add(AddButton); 

    mainPanel.setOpaque(true); 
    setContentPane(mainPanel); 

    pack(); 
    DebugUtils.analyseFrame(this); 
} 

private void addRowActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_addRowActionPerformed 
    mainPanel.revalidate(); 
}//GEN-LAST:event_addRowActionPerformed 

public static void main(String[] args) { 
    javax.swing.SwingUtilities.invokeLater(new Runnable() { 
     @Override 
     public void run() { 
      new ParentNullExample().setVisible(true); 
     } 
    }); 
} 
} 

---

package testing; 

import java.awt.Component; 
import java.awt.Container; 
import java.awt.Dimension; 
import java.awt.GridLayout; 
import javax.swing.BoxLayout; 
import static javax.swing.BoxLayout.Y_AXIS; 
import javax.swing.JPanel; 

public class Panel1 extends JPanel { 

    private JPanel mainPanel; 
    private Dimension preferredSize; 
    private GridLayout tableGridLayout = new GridLayout(0,1); 
    private Boolean isGridLayout; 

    public Panel1(Boolean gridLayout) { 
     isGridLayout = gridLayout; 
     mainPanel = new JPanel(); 
     if (gridLayout) { 
      super.setLayout(tableGridLayout); 
     } 
     else { 
      BoxLayout boxLayout = new BoxLayout(this,Y_AXIS); 
      super.setLayout(boxLayout); 
     } 
     preferredSize = new Dimension(); 
    } 

    @Override 
    public void revalidate() { 
     if (preferredSize == null) preferredSize = new Dimension(); 
     Component superParent = super.getParent(); 
     String superParentName = (superParent == null ? "null" : superParent.getName()) ; 
     Component thisParent = this.getParent(); 
     String thisParentName = (thisParent == null ? "null" : thisParent.getName()) ; 

     System.out.print("revalidate: "+ 
      "Name: "+this.getName()+", "+ 
      "super.Parent: "+superParentName+", "+ 
      "this.Parent: "+thisParentName+", "+ 
      "preferredSize: ["+preferredSize.getHeight() +", "+ 
      preferredSize.getWidth()+"]\n"); 

     if (superParent != null) superParent.revalidate(); 
     if (thisParent != null) thisParent.revalidate(); 
    }; 

    @Override 
    public Dimension getPreferredSize() { 
     return preferredSize; 
    }; 

    @Override 
    public Dimension getMaximumSize() { 
     return new Dimension((int) super.getMaximumSize().getWidth(), (int) preferredSize.getHeight()); 
    }; 

    @Override 
    public Component add(Component c) { 
     super.add(c); 
     preferredSize.setSize(addComponentSize(c, preferredSize)); 
     tableGridLayout.layoutContainer(mainPanel); 
     return null; 
    } 

    public static Dimension addComponentSize(Component c, Dimension sizeSoFar) { 
     int componentWidth = (int) c.getPreferredSize().getWidth(); 
     int panelWidth = (int) sizeSoFar.getWidth(); 
     int width = (panelWidth > componentWidth) ? panelWidth : componentWidth; 
     int height = (int) (c.getPreferredSize().getHeight() + sizeSoFar.getHeight()); 
     return new Dimension(width, height); 
    } 

} 

輸出顯示父名稱爲「null.layeredPane」，這是不預期的一個。

revalidate: Name: null, super.Parent: null, this.Parent: null, preferredSize: [0.0, 0.0] 
revalidate: Name: null, super.Parent: null, this.Parent: null, preferredSize: [0.0, 0.0] 
revalidate: Name: null, super.Parent: null, this.Parent: null, preferredSize: [0.0, 0.0] 
revalidate: Name: null, super.Parent: null, this.Parent: null, preferredSize: [0.0, 0.0] 
1- Frame: Class: testing.ParentNullExample, Name: frame0, H: 61, W: 132 
2|- Container: Name: mainPanel, Class: testing.Panel1, Layout: javax.swing.BoxLayout, H: 23, W: 116 
3|-- Component: Class: testing.Panel1, Name: componentPanel, H: 0, W: 116 
3|-- Component: Class: javax.swing.JButton, Name: AddButton, H: 23, W: 85 


revalidate: Name: mainPanel, super.Parent: null.layeredPane, this.Parent: null.layeredPane, preferredSize: [23.0, 85.0] 
revalidate: Name: mainPanel, super.Parent: null.layeredPane, this.Parent: null.layeredPane, preferredSize: [23.0, 85.0] 

Answer 1

所以，基本上，你似乎有一個API的誤解。一個JFrame由JRootPane，其中包含了JLayeredPane，其中包含了contentPane，JMenuBar和glassPane，如下...

所以，當使用setContentPane(mainPanel);，您要添加mainPanel到JLayeredPane

根據您所提供的代碼的詳細信息