Having looked at menu items with check boxes yesterday, let’s look at another kind of action today: combo boxes.

The most prominent example of a combo box action in MPS or IDEA is the toolbar action that lets you choose a run configuration:

Implementing such an action in MPS again requires us to descend to the Java level because there are no ready-made DSL constructs for combo box actions in the plugin language. We need to extend the com.intellij.openapi.actionSystem.ex.ComboBoxAction class and implement one abstract method, createPopupActionGroup(JComponent component). A sample implementation could look like this:

protected DefaultActionGroup createPopupActionGroup(JComponent component) { 
  // Can use the component parameter with DataManager to obtain
  // context parameters. Example: 
  // MPSDataKeys.MPS_PROJECT.getData(
  //     DataManager.getInstance().getDataContext(component)); 
  return new DefaultActionGroup(
    new ToggleActionExample(1),
    new ToggleActionExample(2),
    new ToggleActionExample(3)); 

The DefaultActionGroup that we return is created dynamically in the example above, but we could also return an existing group defined in the plugin language using the actiongroup expression:

  return actionGroup < ToggleActions >;

To add our new combo box to the main tool bar we need to create another action group, similarly to the way we did it in yesterday’s post:

If we now build our project, we end up with a combo box on the main toolbar that looks like this:

Almost there! How do we give the button a text? The easiest way would have been to invoke a constructor with a String text parameter, except that ComboBoxAction doesn’t provide one. Instead, we can set the text in the constructor via the template presentation:

public ComboBoxActionExample() { 
  getTemplatePresentation().setText("Example Combo Box Action"); 

And now it looks better:

How can we set the combo box text dynamically? To do that, we need to override the update(AnActionEvent) method and write the necessary code to update the presentation:

public void update(@NotNull() AnActionEvent e) { 
  e.getPresentation().setText("Dynamically updated text"); 

If you want to see the code in action, I have updated the sample project on GitHub.