Package org.jdesktop.swingbinding

Class JComboBoxBinding<E,​SS,​TS>

  • Type Parameters:
    E - the type of elements in the source List
    SS - the type of source object (on which the source property resolves to List)
    TS - the type of target object (on which the target property resolves to JComboBox)
    public final class JComboBoxBinding<E,​SS,​TS>
extends AutoBinding<SS,​List<E>,​TS,​List>
    Binds a List of objects to act as the items of a JComboBox. Each object in the source List is an item in the JComboBox. Instances of JComboBoxBinding are obtained by calling one of the createJComboBoxBinding methods in the SwingBindings class.

    Here is an example of creating a binding from a List of Country objects to a JComboBox: 

    
    // create the country list
    List countries = createCountryList();

    // create the binding from List to JComboBox
    JComboBoxBinding cb = SwingBindings.createJComboBoxBinding(READ, countries, jComboBox);

    // realize the binding
    cb.bind();

    If the List is an instance of ObservableList, then changes to the List contents (such as adding, removing or replacing an object) are reflected in the JComboBox. Important: Changing the contents of a non-observable List while it is participating in a JComboBoxBinding is unsupported, resulting in undefined behavior and possible exceptions.

    JComboBoxBinding requires extra clarification on the operation of the refresh and save methods and the meaning of the update strategy. The target property of a JComboBoxBinding is not the target JComboBox property provided in the constructor, but rather a private synthetic property representing the List of objects to show in the target JComboBox. This synthetic property is readable/writeable only when the JComboBoxBinding is bound and the target JComboBox property is readable with a non-null value.

    It is this private synthetic property on which the refresh and save methods operate; meaning that these methods simply cause syncing between the value of the source List property and the value of the synthetic target property (representing the List to be shown in the target JComboBox). These methods do not, therefore, have anything to do with refreshing values in the JComboBox. Likewise, the update strategy, which simply controls when refresh and save are automatically called, also has nothing to do with refreshing values in the JComboBox.

    Note: At the current time, the READ_WRITE update strategy is not useful for JComboBoxBinding. To prevent unwanted confusion, READ_WRITE is translated to READ by JComboBoxBinding's constructor.

    JComboBoxBinding works by installing a custom model on the target JComboBox, as appropriate, to represent the source List. The model is installed on a target JComboBox with the first succesful call to refresh with that JComboBox as the target. Subsequent calls to refresh update the elements in this already-installed model. The model is uninstalled from a target JComboBox when either the JComboBoxBinding is unbound or when the target JComboBox property changes to no longer represent that JComboBox. Note: When the model is uninstalled from a JComboBox, it is replaced with a DefaultComboBoxModel, in order to leave the JComboBox functional.

    Some of the above is easier to understand with an example. Let's consider a JComboBoxBinding (binding), with update strategy READ, between a property representing a List (listP) and a property representing a JComboBox (jComboBoxP). listP and jComboBoxP both start off readable, referring to a non-null List and non-null JComboBox respectively. Let's look at what happens for each of a sequence of events:

    SequenceEventResult
    1 explicit call to binding.bind() - synthetic target property becomes readable/writeable
    - refresh() is called
    - model is installed on target JComboBox, representing list of objects
    2 listP changes to a new List - refresh() is called
    - model is updated with new list of objects
    3 jComboBoxP changes to a new JComboBox - model is uninstalled from old JComboBox
    4 explicit call to binding.refresh() - model is installed on target JComboBox, representing list of objects
    5 listP changes to a new List - refresh() is called
    - model is updated with new list of objects
    6 explicit call to binding.unbind() - model is uninstalled from target JComboBox

    Notice that in step 3, when the value of the JComboBox property changed, the new JComboBox did not automatically get the model with the elements applied to it. A change to the target value should not cause an AutoBinding to sync the target from the source. Step 4 forces a sync by explicitly calling refresh. Alternatively, it could be caused by any other action that results in a refresh (for example, the source property changing value, or an explicit call to unbind followed by bind).

    In addition to binding the items of a JComboBox, it is possible to bind to the selected item of a JComboBox. See the list of interesting swing properties in the package summary for more details.

    Author:
    Shannon Hickey