来自对象数组列表的 JComboBox 值

Question

lately I have come to a problem where I have ArrayList filled with objects

ArrayList<Item> allItems;

while each of Item objects has its own attributes like String name or int value . In my graphical interface I want to have JComboBox filled only with name value of every Item object in allItems ArrayList. Objects inside of allItems are added in runtime of my program and it has no values in the beginning. After I add a new item into my ArrayList I call

comboBox.setModel(new javax.swing.DefaultComboBoxModel(allItems.toArray()));

but this only gives me something like items.Item@283ae01 for example. Is it possible to have displayed only the values String name of each item from ArrayList in ComboBox?

Answer 1

The default renderer uses the toString method of the objects in the list to render the items. You can either a) Override to the toString method of the class added to the JComboBox to provide the proper rendering of the name

@Override
public String toString(){
    return name;
}

or b) provide a custom renderer for the JComboBox which customizes the Component used to render the items in the JComboBox

ListCellRenderer renderer = new DefaultListCellRenderer(){
    @Override
    public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
        Component c = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
        if ( value == null ){
            return c;
        }
        if ( c instanceof JLabel ){
            JLabel label = (JLabel)c;
            Test t = (Test)value;
            label.setText(t.getName());
        }
        return c;
    }
};
myComboBox.setRenderer(renderer);

Note the above is pre-java 7 syntax. In java 7 and above these classes are parametized using generics.

You could further create your own model backed by the List, so when items are added to the List you fire the appropriate listeners to notify the JComboBox of the change (rather than recreating the model every time).

There are other examples for this and more in the java tutorial on using JComboBoxes

Answer 2

You need to create a custom renderer to display the appropriate property from your class. However the custom renderer is only half the solution since you will break the default functionality of the combo box to select an item using the keyboard.

See Combo Box With Custom Renderer for an implementation that does the rendering and still allows the keyboard selection of and item in the combo box.