Swing Jcombobox将第一个元素设置为默认选中的

Question

String[] bookArray={"a","b","c"}; 
    JComboBox bookComboBox = new JComboBox(bookArray); 
    bookComboBox.setSelectedIndex(0); 
    bookComboBox.addActionListener(new ActionListener() { 
     public void actionPerformed(ActionEvent e) { 
      JComboBox cb= (JComboBox) e.getSource(); 
      bookNameSelected=(String) cb.getSelectedItem(); 
      System.out.println("book name selected:"+bookNameSelected); 
      } 
    }); 

下拉的第一个元素显示为默认值，但如果用户未选择任何值，则不会将其作为默认选定值传递。

Answer 1

移动bookComboBox.setSelectedIndex(0);的ActionListener登记后，这允许ActionListener被触发，并设置bookNameSelected

String[] bookArray = {"a", "b", "c"}; 
JComboBox bookComboBox = new JComboBox(bookArray); 
bookComboBox.addActionListener(new ActionListener() { 
    public void actionPerformed(ActionEvent e) { 
     JComboBox cb = (JComboBox) e.getSource(); 
     bookNameSelected = (String) cb.getSelectedItem(); 
     System.out.println("book name selected:" + bookNameSelected); 
    } 
}); 
bookComboBox.setSelectedIndex(0);