我在使用Netbeans的JPanel的可见性问题;我举了一个简单的例子来说明会发生什么。Netbeans创建代码时，我设计的组合和面板->，直到"私有void TheFrame(java.awt.event.)"。WindowEvent evt)"。
在框架的windowActivated中，我放置了panelOne(JPanel).setVisible(false)和这是可行的!从组合中选择一个项目(item2/item4)后，我希望显示panelOne，但这不起作用。
/**
*
* @author Alessandro
*/
public class UIFrame extends javax.swing.JFrame {
/**
* Creates new form UIFrame
*/
public UIFrame() {
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() {
panelOne = new javax.swing.JPanel();
comboBox = new javax.swing.JComboBox();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
addWindowListener(new java.awt.event.WindowAdapter() {
public void windowActivated(java.awt.event.WindowEvent evt) {
TheFrame(evt);
}
});
javax.swing.GroupLayout panelOneLayout = new javax.swing.GroupLayout(panelOne);
panelOne.setLayout(panelOneLayout);
panelOneLayout.setHorizontalGroup(
panelOneLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGap(0, 349, Short.MAX_VALUE)
);
panelOneLayout.setVerticalGroup(
panelOneLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGap(0, 52, Short.MAX_VALUE)
);
comboBox.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Item 1", "Item 2", "Item 3", "Item 4" }));
comboBox.addItemListener(new java.awt.event.ItemListener() {
public void itemStateChanged(java.awt.event.ItemEvent evt) {
ItemListener(evt);
}
});
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(30, 30, 30)
.addComponent(panelOne, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createSequentialGroup()
.addGap(122, 122, 122)
.addComponent(comboBox, javax.swing.GroupLayout.PREFERRED_SIZE, 143, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addContainerGap(21, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(comboBox, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(33, 33, 33)
.addComponent(panelOne, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap(175, Short.MAX_VALUE))
);
pack();
}// </editor-fold>
private void TheFrame(java.awt.event.WindowEvent evt) {
panelOne.setVisible(false);
}
private void ItemListener(java.awt.event.ItemEvent evt) {
String test = (String)(evt.getItem());
switch (test)
{
case "Item1":
panelOne.setVisible(false);
case "Item2":
panelOne.setVisible(true);
case "Item3":
panelOne.setVisible(false);
case "Item4":
panelOne.setVisible(true);
}
}
/**
* @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(UIFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(UIFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(UIFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(UIFrame.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 UIFrame().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JComboBox comboBox;
private javax.swing.JPanel panelOne;
// End of variables declaration
}
您的switch-case不正确。你有错误的字符串的情况下，也你错过了break语句。
已添加的项为
"Item 1", "Item 2", "Item 3" and "Item 4"
而在switch情况下，你比较的是
"item1", "item2", "item3" and "item4"
第二，我认为部分问题在于您获取所选字符串的方式。请尝试使用以下方法:
private void ItemListener(java.awt.event.ItemEvent evt) {
String test = (String) (evt.getItem()); //do not use this
System.out.println(test);
JComboBox box = (JComboBox)evt.getSource();
String selectedString = (String) box.getSelectedItem();
switch (selectedString) { //replaced test with selectedString
case "Item 1":
panelOne.setVisible(false); break;
case "Item 2":
panelOne.setVisible(true); break;
case "Item 3":
panelOne.setVisible(false); break;
case "Item 4":
panelOne.setVisible(true); break;
}
}
我希望这对你有帮助。问题的原因可能是，当更改组合框中的项时，会触发两次项选择更改事件。首先是未选中的项，然后是选中的项。
您可以看到，我已经为test和新的selectedString变量添加了println()。现在，如果你当前选择的是"Item 1"，而你选择了"Item 3"，那么两个ItemEvent将被触发，test的值将在这两种情况下不同，因为它指的是不同的项目，而选中的项目将是相同的，正如你可能想要的。
PS:这就是为什么你需要break语句。当你写:
switch(var){
case 1: doOne();
case 2: doTwo();
case 3: doThree();
}
当case 1成功时，它下面的所有情况都不被检查，并将依次执行。因此，所有doOne(), doTwo()和doThree()将被执行。
switch(var){
case 1: doOne(); break;
case 2: doTwo(); break;
case 3: doThree(); break;
}
这样做的目的是，每当一个case成功并且相应的代码被执行时，break将终止switch-case，从而只执行您想要执行的代码。
还有，这里是我的代码
import java.awt.BorderLayout;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class UIFrame extends JFrame {
final private JPanel panelOne = new JPanel();
private JComboBox comboBox;
public UIFrame() {
initComponents();
}
private void initComponents() {
setLayout(new BorderLayout());
comboBox = new javax.swing.JComboBox();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
comboBox.setModel(new javax.swing.DefaultComboBoxModel(new String[] {
"Item 1", "Item 2", "Item 3", "Item 4" }));
comboBox.addItemListener(new java.awt.event.ItemListener() {
public void itemStateChanged(java.awt.event.ItemEvent evt) {
ItemListener(evt);
}
});
panelOne.add(new JTextField("Hello"));
add(comboBox, BorderLayout.CENTER);
add(panelOne, BorderLayout.NORTH);
}
private void ItemListener(java.awt.event.ItemEvent evt) {
panelOne.setVisible(false);
String test = (String) (evt.getItem());
System.out.println(test);
JComboBox box = (JComboBox)evt.getSource();
String selectedString = (String) box.getSelectedItem();
switch (selectedString) {
case "Item 1":
panelOne.setVisible(false);
break;
case "Item 2":
panelOne.setVisible(true);
break;
case "Item 3":
panelOne.setVisible(false);
break;
case "Item 4":
panelOne.setVisible(true);
break;
}
}
public static void main(String[] args) {
final UIFrame frame = new UIFrame();
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
frame.pack();
frame.setVisible(true);
}
});
}
}
如果你使用if ...else而不是switch Statement，那么如果你是java语言的新手，它更容易编码，也更容易理解。
在jComboBox event
试一下这段代码private void jComboBox1ItemStateChanged(java.awt.event.ItemEvent evt) {
PanelChange();
}
private void PanelChange() {
String test = jComboBox1.getSelectedItem().toString();
if (test.equals("Item 1") || test.equals("Item 3")) {
jPanel1.setVisible(false);
}else{
jPanel1.setVisible(true);
}
}
public UIFrame() {
initComponents();
PanelChange();
}