Java Swing组件下拉菜单控件JComboBox用法示例

Z时代
2024-01-10
分类：IT

本文实例讲述了Java Swing组件下拉菜单控件JComboBox用法。分享给大家供大家参考，具体如下：

JComboBox是Swing中的下拉菜单控件。它永远只能选中一个项目，然而比单选按钮节省空间。如果使用setEditable设置为true则内部选项的文本可以编辑，因此这种组件被称为组合框。注意，对选项的编辑只会影响当前项，而不会改变列表内容。可以使用addItem方法来添加选项列表，或者使用insertItemAt在任何位置插入选项；然而如果有大量选项需要添加，这种方法是非常笨重的，可以先构造一个DefaultComboBoxModel，使用addElement加载选项，最后在调用JComboBox的setModel方法。

常用方法如下：

示例代码：

JComboBoxBasicUseDemo.java

package awtDemo;
import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.event.PopupMenuEvent;
import javax.swing.event.PopupMenuListener;
/*
 * 演示JComboBox的基本用法，以及事件响应
 */
public class JComboBoxBasicUseDemo extends JFrame{
  private static final long serialVersionUID = -8161981948004677531L;
  int DEFAULT_WIDTH = 600;
  int DEFAULT_HEIGHT = 400;
  private JLabel label;
  private JComboBox<String> faceCombo;
  private static final int FONTSIZE = 12;  
  @SuppressWarnings("unused")
    public JComboBoxBasicUseDemo(){
    setTitle("JComboBoxDemo - www.webkf.net");
    setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
    //添加label
    label = new JLabel("欢迎来到 www.webkf.net");
    label.setFont(new Font("Serif",Font.PLAIN, FONTSIZE));
    add(label, BorderLayout.CENTER);
    //actionListener
    ActionListener actionListener = new ActionListener(){
      public void actionPerformed(ActionEvent e) {
        if(e.getSource() instanceof JComboBox){
          @SuppressWarnings({ "unchecked", "rawtypes" })
          JComboBox<String> comboBox = (JComboBox)e.getSource();
          String fontName = comboBox.getSelectedItem().toString();
          label.setFont(new Font(fontName, Font.PLAIN, FONTSIZE));
          System.out.printf("%s%n", "actionPerformed called");
        }
      }
    };
    //popupMenuListener
    PopupMenuListener popupMenuListener = new PopupMenuListener() {
      @Override
      public void popupMenuCanceled(PopupMenuEvent e) {
        System.out.println("下拉菜单取消");
      }
      @SuppressWarnings("unchecked")
            @Override
      public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {
        System.out.println("下拉菜单合上");
        JComboBox<String> source = (JComboBox<String>)e.getSource();
      }
      @Override
      public void popupMenuWillBecomeVisible(PopupMenuEvent e) {
        System.out.println("下拉菜单弹出");
      }
    };
    //itemListener
    ItemListener itemListener = new ItemListener() {
      @Override
      public void itemStateChanged(ItemEvent arg0) {
        // TODO Auto-generated method stub
        if(ItemEvent.SELECTED == arg0.getStateChange()){
          String selectedItem = arg0.getItem().toString();
          label.setFont(new Font(selectedItem, Font.PLAIN, FONTSIZE));
          System.out.printf("new selected item : %s%n",selectedItem);
        }
        if(ItemEvent.DESELECTED == arg0.getStateChange()){
          String selectedItem = arg0.getItem().toString();
          System.out.printf("deselected item : %s%n",selectedItem);
        }
      }
      };
    //添加一个JComboBox
    faceCombo = new JComboBox<String>();
    faceCombo.setEditable(true);
    //faceCombo.addActionListener(actionListener);
    //faceCombo.addPopupMenuListener(popupMenuListener);
    faceCombo.addItemListener(itemListener);
    faceCombo.setEnabled(true);
    faceCombo.addItem("Serif");
    faceCombo.addItem("SansSerif");
    faceCombo.addItem("Monospaced");
    faceCombo.addItem("Dialog");
    faceCombo.addItem("DialogInput");
    add(faceCombo, BorderLayout.SOUTH);
  }
  public static void main(String[] args) {
    // TODO Auto-generated method stub
    //创建窗体并指定标题
    JComboBoxBasicUseDemo frame = new JComboBoxBasicUseDemo();
    //关闭窗体后退出程序
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    //自动适配所有控件大小
    //frame.pack();
    //设置窗体位置在屏幕中央
    frame.setLocationRelativeTo(null);
    //显示窗体
    frame.setVisible(true);
  }
}