intellij-sdk-code-samples/tutorials/action_system/working_with_custom_actions.md

title
1. Registering an Action

An action is technically a class, derived from the AnAction class. To update the state of the action, the method AnAction.update(AnActionEvent) is called by the IntelliJ Platform framework. The object of type AnActionEvent passed to this method carries the information about the current context for the action, and in particular, the specific presentation which needs to be updated.

1.1. Creating actions

To create a new action we need to extend the AnAction class. As an example we will do that in the SimplePopDialogAction class in the register_actions code sample.

public class SimplePopDialogAction extends AnAction {
}

Note the SimplePopDialogAction does not have class fields of any kind. This is because an instance of AnAction class exists for the entire lifetime of the application. If AnAction class uses a field to store data which has a shorter lifetime, and doesn't clear this data promptly, the data will be leaked. For example, any AnAction data that exists only within the context of a Project will cause the Project to be kept in memory after the user has closed it.

1.2. Overriding actionPerformed()

The AnAction class is abstract, and classes that extend it must override the AnAction.actionPerformed(AnActionEvent) method. This method should contain the code to be executed when the action has been invoked. In this case SimplePopDialogAction.actionPerformed(AnActionEvent) doesn't do anything yet.

public class SimplePopDialogAction extends AnAction {
  @Override
  public void actionPerformed(@NotNull AnActionEvent anActionEvent) {
    // Using the event, create and show a dialog
  }
}

1.3. Registering actions

To register a newly created action, an <action> attribute should be added to the <actions> section of the plugin configuration file plugin.xml. IntelliJ IDEA has an embedded inspection that spots unregistered actions. Here is an example using the SimplePopDialogAction class:

To register SimplePopDialogAction and set up its attributes press Alt + Enter while the caret is placed on the action's declaration.

Then fill out the New Action form to set up SimplePopDialogAction's parameters such as: the action's name and description, a UI component the action is bound to, the visual position of the menu item the action is bound to, and a shortcut for invoking the action. In this case SimplePopDialogAction would be available in the Tools Menu, it would be placed on top, and would have no shortcuts.

In this example, after completing the New Action form and applying the changes, the <actions> section of the plugin's plugins.xml file would now contain:

<actions>
    <!-- Add your actions here -->
    <action id="org.jetbrains.tutorials.actions.SimplePopDialogAction"
            class="org.jetbrains.tutorials.actions.SimplePopDialogAction" text="Simple Action"
            description="IntelliJ Action System Demo">
      <add-to-group group-id="ToolsMenu" anchor="first"/>
    </action>
</actions>

This declaration is adequate, but as we'll see in the next section there are more elements that can be added to the declaration.

1.4. Setting attributes manually

You can configure additional attributes of the action by adding them to the New Action form or by editing its registration in the plugin.xml file. Please refer to the Action System documentation for the full list of supported attributes.

The <action> declaration for SimplePopDialogAction in the register_actions plugin.xml file actually contains elements for <keyboard-shortcut> and <mouse-shortcut>. The full declaration is:

<action id="org.jetbrains.tutorials.actions.SimpleAction" class="org.jetbrains.tutorials.actions.SimplePopDialogAction"
        text="Simple Action" description="IntelliJ Action System Demo">
  <keyboard-shortcut first-keystroke="control alt A" second-keystroke="C" keymap="$default"/>
  <mouse-shortcut keystroke="control button3 doubleClick" keymap="$default"/>
  <add-to-group group-id="ToolsMenu" anchor="first"/>
</action>

The plugin.xml file contains copious comments about the declaration.

After performing the steps described above we need to compile and run the plugin to the newly created action available as a Tools Menu item:

1.5. Performing an action

In order to make the action do something we need to add code to the SimplePopDialoigAction.actionPerformed(AnActionEvent) method. The following code gets information from the anActionEvent input parameter and constructs a simple message dialog. A generic icon, and the description and text attributes from the invoking menu action are displayed.

For demonstration purposes the AnActionEvent.getData() method tests if a Navigatable object is available, meaning e.g. an element has been selected in the editor. If so, information about the selected element is opportunistically added to the dialog.

@Override
public void actionPerformed(@NotNull AnActionEvent anActionEvent) {
    // Using the event, create and show a dialog
    Project currentProject = anActionEvent.getProject();
    StringBuffer dlgMsg = new StringBuffer(anActionEvent.getPresentation().getText() + " Selected!");
    String dlgTitle = anActionEvent.getPresentation().getDescription();
    // If an element is selected in the editor, add info about it.
    Navigatable nav = anActionEvent.getData(CommonDataKeys.NAVIGATABLE);
    if (nav != null) {
      dlgMsg.append(String.format("\nSelected Element: %s", nav.toString()));
    }
Messages.showMessageDialog(currentProject, dlgMsg.toString(), dlgTitle, Messages.getInformationIcon());
}

1.6. Setting up an action's visibility and availability

To control the action's visibility and availability we need to override the AnAction.update(AnActionEvent) method. The default implementation of this method does nothing, which means the action is always disabled. Override this method to provide the ability to dynamically change action's state and(or) presentation depending on the context.

In this example the SimplePopDialogAction.actionPerformed(AnActionEvent) method relies on a Project object being available. So the SimplePopDialogAction.update(AnActionEvent) method disables the action for contexts where aProject object isn't defined:

@Override
public void update(AnActionEvent anActionEvent) {
    // Set the availability based on whether a project is open
    Project project = anActionEvent.getProject();
    anActionEvent.getPresentation().setEnabledAndVisible(project != null);
}

Parameter anActionEvent carries information on the invocation place and data available. Note the update() method does not check to see if a Navigatable object is available before enabling SimplePopDialogAction. This is done for the purposes of demonstration code.

Note This method can be called frequently: for instance, if an action is added to a toolbar, it will be updated twice a second. This means that this method is supposed to work really fast; no real work should be done at this phase. For example, checking selection in a tree or a list, is considered valid but working with the file system is not. If you cannot understand the state of the action fast you should do it in the AnActionEvent method and notify the user that the action cannot be executed if it's the case.

After compiling and running the plugin project and invoking the action, the dialog will pop up: