java - 检查可编辑的 jcombobox

Question

我无法在 keyTyped 方法的 if 检查中借出。部分代码如下:

这里我初始化组合框:

private void initComponents()
{
    this.cboDayModel = new DefaultComboBoxModel<ListItem>();
    this.cboDay = new JComboBox<ListItem>( this.cboDayModel );
    this.cboDay.addItemListener( this );
    this.cboDay.setName( "cboDay" );
    this.cboDay.setBackground( this.einAusClass.hPHB.btnColor );
    this.cboDay.setEditable( true );
    this.cboDay.getEditor().getEditorComponent().addKeyListener( this );
    this.cboDay.getEditor().getEditorComponent().addFocusListener( this );
    this.add( this.cboDay );
}

此时我检查输入的内容:

@Override
  public void keyTyped( KeyEvent e )
  {
    if ( !( Character.isDigit( e.getKeyChar() ) ) )
    {
      e.consume();
      return;
    }
    if ( e.getSource() instanceof JComboBox )  // <-------*************
    {
      System.out.println( "zz2" );
      this.cbo = (JComboBox<ListItem>) e.getSource();

      String str = ( (JTextField) cbo.getEditor().
                          getEditorComponent() ).getText();
      int zahl = Integer.parseInt( "0" + str );
      System.out.println( str + "" + zahl );
      if ( this.cbo == cboDay )
      {
        if ( zahl < 1 || zahl > 31 )
        {
          e.consume();
          return;
        }
      }
  }
}

在 keyTyped 方法中我确实检查

if ( e.getSource() instanceof JComboBox )

为什么它不进入这个 if 语句内部？

Answer 1

根据 https://docs.oracle.com/javase/7/docs/api/java/util/EventObject.html，

e.getSource() 不会返回 JComboBox 的 对象这是 getSource() 的方法声明；public Object getSource() 这将返回最初发生 Event 的 object，因此您应该实际进行强制转换e.getSource 到 jcombobox 的对象 例如:

if(cboDay == (jcombobox)e.getSource())

您可以使用 actioncommand 实现相同的功能，例如:

 cboDay.setActionCommand("combo"); 

 public void keyTyped( KeyEvent e )
     String action = e.getActionCommand();
      if (action.equals("combo")) {
      System.out.println("done!");
      }
 }