jTree節點選擇

Question

我有帶jTree和displayPanel的Main JFrame ，還有FirstPanel和SecondPanel。 通過單擊jTree節點，將選擇每個jPanels 。

這是代碼：

package demo;

import java.awt.CardLayout;
import java.awt.event.MouseEvent;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;
import javax.swing.tree.TreeSelectionModel;

public class Main extends javax.swing.JFrame {

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

        treePanel = new javax.swing.JPanel();
        jScrollPane1 = new javax.swing.JScrollPane();
        jTree1 = new javax.swing.JTree();
        displayPanel = new javax.swing.JPanel();
        firstPanel = new demo.FirstPanel();
        secondPanel = new demo.SecondPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        javax.swing.tree.DefaultMutableTreeNode treeNode1 = new javax.swing.tree.DefaultMutableTreeNode("Main");
        javax.swing.tree.DefaultMutableTreeNode treeNode2 = new javax.swing.tree.DefaultMutableTreeNode("Unit");
        javax.swing.tree.DefaultMutableTreeNode treeNode3 = new javax.swing.tree.DefaultMutableTreeNode("time");
        treeNode2.add(treeNode3);
        treeNode3 = new javax.swing.tree.DefaultMutableTreeNode("velocity");
        treeNode2.add(treeNode3);
        treeNode1.add(treeNode2);
        jTree1.setModel(new javax.swing.tree.DefaultTreeModel(treeNode1));
        jTree1.addTreeSelectionListener(new javax.swing.event.TreeSelectionListener() {
            public void valueChanged(javax.swing.event.TreeSelectionEvent evt) {
                jTree1ValueChanged(evt);
            }
        });
        jScrollPane1.setViewportView(jTree1);

        treePanel.add(jScrollPane1);

        getContentPane().add(treePanel, java.awt.BorderLayout.WEST);

        displayPanel.setLayout(new java.awt.CardLayout());
        displayPanel.add(firstPanel, "first");
        displayPanel.add(secondPanel, "second");

        getContentPane().add(displayPanel, java.awt.BorderLayout.CENTER);

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

    private void jTree1ValueChanged(javax.swing.event.TreeSelectionEvent evt) {                                    
         String node = evt.getNewLeadSelectionPath().getLastPathComponent().toString();
         if (node == null)
         return;
    if( node.equals("time") ) {
        displayPanel.add(firstPanel);
    } else if( node.equals("velocity") ) {
       displayPanel.add(secondPanel);
    }

    }                                   

    /**
     * @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(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(Main.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 Main().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JPanel displayPanel;
    private demo.FirstPanel firstPanel;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTree jTree1;
    private demo.SecondPanel secondPanel;
    private javax.swing.JPanel treePanel;
    // End of variables declaration                   
}

問題出在哪里：

private void jTree1ValueChanged(javax.swing.event.TreeSelectionEvent evt) {                                    
         String node = evt.getNewLeadSelectionPath().getLastPathComponent().toString();
         if (node == null)
         return;
    **if( node.equals("time") ) {
        displayPanel.add(firstPanel);
    } else if( node.equals("velocity") ) {
       displayPanel.add(secondPanel);**
    }

當我單擊時間節點時，它向我顯示secondPanel ；當單擊速度節點時，它向我顯示firstPanel 。 我不知道如何切換它們。 問題是：如何使該時間節點顯示firstPanel ， 速度節點顯示secondPanel ？

先感謝您。

Answer 1

這是問題所在：

displayPanel.add(firstPanel);
...
displayPanel.add(secondPanel);

您試圖將組件添加到已經顯示的容器中，並且組件的層次結構無效 。 動態添加/刪除組件時，您需要重新驗證組件層次結構：

displayPanel.add(firstPanel);
displayPanel.revalidate(); // calls the layout manager
displayPanel.repaint(); // repaints the component

但是恕我直言，這是CardLayout的絕佳用例（鏈接到教程）。 我建議你這種方法：

1. 在要顯示面板的區域中放置一個帶有CardLayout的cardPanel 。
2. 使用適當的約束（例如： time和velocity ），將所有面板（ firstPanel ， secondPanel ，...）添加到此cardPanel 。
3. 在更改樹形選擇時，使用CardLayout方法show（cardPanel，Constraint）切換面板，其中constraint是用於將面板添加到cardPanel 。