在Java Netbeans生成的组合框中添加元素

Question

我在向组合框中添加新元素时遇到了一些问题。代码是由Netbeans Form Editor创建的，因此我只能修改事件侦听器。元素无法预定义，因为这些元素在数据库中并且不断扩展。目前组合框只有一个元素，我希望它能根据数据库中的值进行更新。谢谢大家抽出时间。

package Interface;
/**
 *
* @author Raam
 */
public class Welcome extends javax.swing.JFrame {
/**
 * Creates new form Welcome
 */
public Welcome() {
    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() {
    jComboBox1 = new javax.swing.JComboBox();
    jComboBox2 = new javax.swing.JComboBox();
    jButton1 = new javax.swing.JButton();
    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setTitle("addNewRecord");
    jComboBox1.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Add New Record", "Class", "Section", "Student" }));
    jComboBox1.setToolTipText("Add New Record");
    jComboBox1.setName("AddNewRecord"); // NOI18N
    jComboBox1.addFocusListener(new java.awt.event.FocusAdapter() {
        public void focusGained(java.awt.event.FocusEvent evt) {
            jComboBox1FocusGained(evt);
        }
    });
    jComboBox2.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Choose Class" }));
    jComboBox2.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jComboBox2ActionPerformed(evt);
        }
    });
    jButton1.setText("Open Database");
    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(51, 51, 51)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jButton1)
                .addGroup(layout.createSequentialGroup()
                    .addComponent(jComboBox1, javax.swing.GroupLayout.PREFERRED_SIZE, 106, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addGap(41, 41, 41)
                    .addComponent(jComboBox2, javax.swing.GroupLayout.PREFERRED_SIZE, 116, javax.swing.GroupLayout.PREFERRED_SIZE)))
            .addContainerGap(86, Short.MAX_VALUE))
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(45, 45, 45)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(jComboBox1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(jComboBox2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
            .addComponent(jButton1)
            .addContainerGap(16, Short.MAX_VALUE))
    );
    pack();
}// </editor-fold>                        
private void jComboBox2ActionPerformed(java.awt.event.ActionEvent evt) {                                           
    // TODO add your handling code here:
}                                          
private void jComboBox1FocusGained(java.awt.event.FocusEvent evt) {                                       
    jComboBox1.addElement(); //Tried this, not working
}                                      
/**
 * @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(Welcome.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(Welcome.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(Welcome.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(Welcome.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 Welcome().setVisible(true);
        }
    });
}
// Variables declaration - do not modify                     
private javax.swing.JButton jButton1;
private javax.swing.JComboBox jComboBox1;
private javax.swing.JComboBox jComboBox2;
// End of variables declaration                   

}

Answer 1

您必须在模型中添加项目：

DefaultComboBoxModel model = (DefaultComboBoxModel) jComboBox1.getModel();
model.addElement("new ítem");

Answer 2

可以通过转到组合框的属性，然后转到>>模型来完成。正如这里提供的答案https://stackoverflow.com/a/39689417/5737654