java - 选择时的组合框

Question

我试图在选择一个选项时获取组合框，它会执行诸如打印一些文本之类的操作，但经过数小时的尝试后我不知道该怎么做。我知道它与事件监听器。刚接触java。如有任何帮助，我们将不胜感激。

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JComboBox;

public class Frame extends JFrame
{
    //Instance Variables.
     private static final int FRAME_WIDTH = 500;
     private static final int FRAME_HEIGHT = 400;


     public Frame()
     {
        Venue1();
        setSize(FRAME_WIDTH, FRAME_HEIGHT);
     }

     private void Venue1()
     {
         //String [] Venues = {"Elvis","Gorillaz", "Imagine Dragons","Michael Jackson"};

         JComboBox DropMenu = new JComboBox();
         DropMenu.addItem("Elvis");
         DropMenu.addItem("Gorillaz");
         DropMenu.addItem("Imagine Dragons");
         DropMenu.addItem("Michael Jackson");
         DropMenu.setEditable(false);
         DropMenu.setVisible(true);

         JPanel panel = new JPanel();
         JLabel label = new JLabel("Pick a venue");

         add(panel);
         panel.add(label);
         panel.add(DropMenu);

        ActionListener listener = new listener();
        DropMenu.addActionListener(listener);

     }//End of Venue Method.
}//End of class.

//Button Listeners

class listener implements ActionListener
{
    public void actionPerformed(ActionEvent event)
    {

    }
}

    enter code here

Answer 1

• 要从 JComboBox 中获取选定的值，就这么简单:

DropMenu.getSelectedValue();

• 更改选择时获取选择:

  MyItemListener actionListener = new MyItemListener();
  DropMenu.addItemListener(actionListener);
  
  class MyItemListener implements ItemListener {
      // This method is called only if a new item has been selected.
      public void itemStateChanged(ItemEvent evt) {
          JComboBox DropMenu = (JComboBox) evt.getSource();
          Object item = evt.getItem();
          if (evt.getStateChange() == ItemEvent.SELECTED) {
              // Item was just selected
          } else if (evt.getStateChange() == ItemEvent.DESELECTED) {
             // Item is no longer selected
          }
      }
  }