动态注册侦听器

Question

I have created UI that populates components dynamically. The UI is like table, which has X number of rows, but having 4 components [1 JLable, 3 JComboboxes] in each row. I want to register listeners for all comboboxes, to fetch the selectedItem() from comboboxes and use it for further reference. But, I am not able to do it using my existing code. The code is below.

    for(int i=0; i< list.size(); i++) {
        final int j = i;

        cb1[i] = new JCombobx();
        masterPanel[i].add(cb1[i]);

        cb2[i] = new JCombobx();
        masterPanel[i].add(cb2[i]);

        cb3[i] = new JCombobx();
        masterPanel[i].add(cb3[i]);

            cb1[j].addItem("Select Value");
            for (OtherObject l : List) {
                cb1[j].addItem(l);
            }

        cb1[j].addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                selectedValue = (SomeObject) cb1[j].getSelectedItem();
            }
        }); 
    }

I am getting this exception :

    java.lang.ClassCastException: java.lang.String cannot be cast to SomeObject 

In this, combobox[cb2] will be populated according to the value selected from cb1 and eventually third combobox will be populated according to the value selected from cb2. What's wrong in it?

Answer 1

The exception is very clear: obviously, you put strings into your first combo box object (in the code that you aren't showing here).

A string object can never be casted to (SomeObject) class.

So, there are two ways to fix that:

1. You look into the code that actually adds the values to your first combo box. That code should be adding instances of SomeObject, if you want to use SomeObject
2. Or, if it is correct that your first box works with strings; then you have to change your code that currently tries to cast the string returned by getSelectedItem() ... to not cast!