java - 如何更改 JComboBox 的选定值

Question

我有两个组合框，基于在第一个组合框中所做的选择，第二个框的选定值应该改变。请在下面找到代码片段:

secondcombobox.setSelectedItem(firstcombobox.getSelectedItem());

Answer 1

你应该使用 ActionListener :

firstcombobox.addActionListener(new ActionListener(){

   void actionPerformed(ActionEvent e){
       // sets the selected item of secondcombobox to be the value of firstcombobox
       // assuming secondcombobox contains such a value.
       secondcombobox.setSelectedItem(firstcombobox.getSelecteditem());
    }

});

注意这里的范围很重要。您可以将 firstcombobox 和 secondcombobox 设为全局或最终，或者您可以使用稍微替代的形式，将这些参数作为构造函数的输入:

firstcombobox.addActionListener(new ActionListener(firstcombobox, secondcombobox){
   private JComboBox a;
   private JComboBox b;

   public ActionListner(JComboBox a, JComboBox b){
       this.a = a;
       this.b = b;
   }

   void actionPerformed(ActionEvent e){
       // sets the selected item of a to be the value of b
       // assuming a contains such a value.
       b.setSelectedItem(a.getSelecteditem());
    }

});