jcomboBox-空项没有itemEvents

空对象在 JComboBox . 例如,组合框的 getSelectedIndex 如果对象是-1,则在选择项时激发的方法将返回-1。 null . 也可能有其他方法执行空检查,并可能返回不正确的结果。

如果您真的需要这个功能,最好使用包装器对象。例如:

class StringWrapper{
    final String s;
    public StringWrapper(String s){
        this.s=s;
    }
    @Override
    public String toString() {
        return s;
    }
}

final JComboBox cb = new JComboBox(new StringWrapper[]{ 
            new StringWrapper(null), 
            new StringWrapper("one"),
            new StringWrapper("two"),
            new StringWrapper("three")});

好吧,我很蠢…只需子类jcombobox并添加:

@Override
protected void selectedItemChanged() {
    fireItemStateChanged(new ItemEvent(this, ItemEvent.ITEM_STATE_CHANGED,
            selectedItemReminder,
            ItemEvent.DESELECTED));
    selectedItemReminder = dataModel.getSelectedItem();

    fireItemStateChanged(new ItemEvent(this, ItemEvent.ITEM_STATE_CHANGED,
            selectedItemReminder,
            ItemEvent.SELECTED));
}

我仍然认为JComboBox所描述的行为是不一致和令人困惑的…

如果您希望在选择一个条目时触发一次操作,包括空值…

import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.JComboBox;
import javax.swing.JOptionPane;

public class ComboBoxTest {
   public static void main(String... args) {
       final JComboBox cb = new JComboBox(new String[]{null, "one","two","three"});
       cb.addItemListener(new ItemListener(){
            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED || cb.getSelectedItem() == null)
                System.out.println(e);
            }
       });
       JOptionPane.showMessageDialog(null, cb);
  }
}