Plugin Writing FAQ.md

How to...

Random things we learned about writing IntelliJ plugins

Listen to editor events

Add classes to plugin.xml (docs)

<idea-plugin>
    <applicationListeners>
      <listener class="myPlugin.MyListenerClass" topic="BaseListenerInterface"/>
    </applicationListeners>
</idea-plugin>

Alternatively, subscribe in code. This can be useful if you e.g. want a widget instance to listen to some events, instead of separate listener/widget instances which communicate.

fun init() {
    project.messageBus.connect().subscribe(
            VirtualFileManager.VFS_CHANGES,
            object : BulkFileListener {
                override fun after(events: MutableList<out VFileEvent>) {
                    super.after(events)
                    /* ... */
                }
            }
    )
}

Listeners

Listen to	Listener
Project open	com.intellij.openapi.project.ProjectManagerListener
File open	org.brex.plugins.codeowners.services.FileService

Add status bar widgets

Status bar widgets require:

1. A Wdiget Factory class which extends from StatusBarWidgetFactory
2. A Widget class which extends from StatusBarWidget (or a subclass e.g. EditorBasedWidget)
3. An entry in the plugin configuration which hooks the factory into the status bar Extension Point:

<idea-plugin>
    <applicationListeners>
      <statusBarWidgetFactory implementation="org.brex.plugins.codeowners.widget.CodeOwnersWidgetFactory"/>
    </applicationListeners>
</idea-plugin>

Note: The name of the XML element (statusBarWidgetFactory) and the name of the interface StatusBarWidgetFactory must match. They are the name of the Extension Point.

Gotchas

• EditorBasedWidget is supposed to keep track of the currently selected & open editor/file, but sometimes it seems to just 'lose' its link to the editor!
  • If you're using it to subscribe to file events, just use the files in the event instead
• Working with files/projects is not as simple as you might imagine. There are...
  • Projects
  • ... which can have multiple modules
  • ... which can be inside and depend on other modules
  • ... all of which can have multiple source roots!
  • So finding "the top level" of a project is not as simple as it might seem.