Making A Mac App Scriptable Tutorial

Allow users to write scripts to control your OS X app – giving it unprecedented usability. Discover how in this “Making a Mac App Scriptable Tutorial”. By Sarah Reichelt.

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Scripting Your App

Before you start, make sure to quit any running instance of the app that Script Editor might have opened.

Build and run Scriptable Tasks; right-click on the icon in the Dock and select Options/Show in Finder. Quit the Script Editor app and restart it to let it pick up the changes to your app.

Open the Library window, and drag the Scriptable Tasks app from the Finder into the Library window.

If you get an error saying the app is not scriptable, try quitting Script Editor and starting it again as it sometimes doesn’t register a freshly built app. If it still fails to import, go back and double-check your changes to the SDEF file.

Double-click Scriptable Tasks in the Library to see the app’s dictionary:

Making a mac app scriptable tutorial: Scriptable Tasks Dictionary 1

You’ll see the Standard Suite and the Scriptable Tasks Suite. Click on the Scriptable Tasks suite, and you will see what you put into the SDEF file. The application contains tasks, and a task has four properties.

Change the scripting language in the dictionary to JavaScript using the Language popup in the toolbar. You will see the same information but with one important change. The cases of classes and properties have changed. I have no idea why this is, but it’s one of those “gotchas” you need to watch out for.

In Script Editor, make a new script file and set the editor to show Log/Replies. Test either of the following scripts, making sure to select the appropriate language in the language pop-up:

tell application "Scriptable Tasks"
  get every task
end tell


app = Application("Scriptable Tasks");

In the log, you will see a list of the tasks by ID. For more useful information, edit the scripts as follows:

tell application "Scriptable Tasks"
  get the name of every task
end tell


app = Application("Scriptable Tasks");;

Making a mac app scriptable tutorial: AppleScript Tasks

Making a mac app scriptable tutorial: JavaScript Tasks

Try out a few more of the sample scripts you downloaded earlier. When running the scripts, make sure you set the Script Editor to show Log/Replies so that you can see the results along the way.

Each script quits the app before running it again; this is to reset the data after any edits so that the sample scripts work as expected. You wouldn’t normally do this in your own scripts.

Note: Script Editor can get very confused as you build updated versions of the app, because it tries to keep a version running at all times if you have an open script that is using the app. This often ends up as an older version of the app, so before every build, quit the app.

If you see two copies of the Scriptable Tasks app running at any time, or if there appears to be a script error in any of the samples, you can be sure that Script Editor has glommed on to the wrong version of the app. The easiest fix is to quit all copies of the app and quit Script Editor. Clean the Xcode build (Product/Clean), then build and run again.

Restart Script Editor and when it opens the script, click Compile and then click Run. And if THAT doesn’t work, delete Derived Data for the app in ~/Library/Developer/Xcode/DerivedData.

Try out the next two sample scripts:

3. Get Tasks.scpt

This script retrieves the number of tasks and the names of tasks using various filters. Make note of the following:

  • JavaScript counts from 0, AppleScript counts from 1.
  • Text searches are case-insensitive.

4. Add Edit Tasks.scpt

This script adds new tasks, toggles the completed flag on the first task, and tries to create a task with the same name as another.

Hmmm… creating a task with the same name worked! Now you have two “Feed the cat” tasks. The cat will be thrilled, but for the purposes of this app, task names should be unique. Trying to add a task with a name that is already in use should have produced an error.

Back in Xcode, look in AppDelegate.swift and you can see that when the script wants to insert an object, the app delegate passes that call to its dataProvider. In DataProvider.swift, look at insertNew(task:at:), which inserts an existing task into the array or appends a new task to the end.

Time to add a check here. Replace the function with the following:

mutating func insertNew(task: Task, at index: Int) -> [Task] {
  // 1
  if taskExists(withTitle: task.title) {
    // 2
    let command = NSScriptCommand.current()
    command?.scriptErrorNumber = errOSACantAssign
    command?.scriptErrorString = "Task with the title '\(task.title)' already exists"
  } else {
    // 3
    if index >= tasks.count {
    } else {
      tasks.insert(task, at: index)


  return tasks

Here’s what each commented section does:

  • Get a reference to the scripting command that called this function.
  • Set the command’s errorNumber and errorString properties; errOSACantAssign is one of the standard AppleScript error codes. These will be sent back to the calling script.
  • Process the task as before.
  • Post a notification of data changes. The ViewController will see this and update the display.
  1. Use an existing function to check if a task with this name already exists.
  2. If the name is not unique:
  3. If the name is unique:

Quit the app if running, then build and run your app. Run the 4. Add Edit Tasks scripts again. This time you should get an error dialog and no duplicate tasks will be created. Sorry about that, cat…

Making a mac app scriptable tutorial: Hungry Cat

5. Delete Tasks.scpt

This script deletes a task, checks if a particular task exists and deletes it if possible, and finally deletes all completed tasks.

Working With Nested Objects

In the sample app, the second column displays a list of tags assigned to each task. So far, you have no way of working with them via scripts – time to fix that!

Object specifiers can handle a hierarchy of objects. That’s what you have here, with the application owning the tasks and each task owning its tags.

As with the Task class, you need to make the Tag scriptable.

Open Tag.swift and make the following changes:

  • Change the class definition line to @objc(Tag) class Tag: NSObject {
  • Add the override keyword to init.
  • Add the object specifier method:
override var objectSpecifier: NSScriptObjectSpecifier {
  // 1
  guard let task = task else { return NSScriptObjectSpecifier() }

  // 2
  guard let taskClassDescription = task.classDescription as? NSScriptClassDescription else {
    return NSScriptObjectSpecifier()
  // 3
  let taskSpecifier = task.objectSpecifier

  // 4
  let specifier = NSUniqueIDSpecifier(containerClassDescription: taskClassDescription,
    containerSpecifier: taskSpecifier, key: "tags", uniqueID: id)
  return specifier

The above code is relatively straightforward:

  1. Check that the tag has an assigned task.
  2. Check that the task has a class description of the correct class.
  3. Get the object specifier for the parent task.
  4. Construct the object specifier for the tag contained inside the task and return it.

Add the following to the SDEF file at the Insert tag class here comment:

<class name="tag" code="TaGg" description="A tag" inherits="item" plural="tags">
  <cocoa class="Tag"/>
  <property name="id" code="ID  " type="text" access="r"
    description="The unique identifier of the tag.">
    <cocoa key="uniqueID"/>
  <property name="name" code="pnam" type="text" access="rw"
    description="The name of the tag.">
    <cocoa key="name"/>

This is very similar to the data for the Task class, but a tag only has two exposed properties: id and name.

Now the Task section has to be edited to indicate that it contains tag elements.

Add the following code to the Task class XML, at the Insert element of tags here comment:

<element type="tag" access="rw">
  <cocoa key="tags"/>

Quit the app, then build and run the app again.

Go back to the Script Editor; if the Scriptable Tasks dictionary is open, close and re-open it. See if it contains information about tags.

If not, remove the Scriptable Tasks entry from the Library and add it again by dragging the app into the window:

Making a mac app scriptable tutorial: Scriptable Tasks Dictionary 2

Try one of the following scripts:

tell application "Scriptable Tasks"
  get the name of every tag of task 1
end tell


app = Application("Scriptable Tasks");

The app now lets you retrieve tags – but what about adding new ones?

You may have noticed in Tag.swift that each Tag object has a weak reference to its owning task. That helps create the links when getting the object specifier, so this task property must be set when assigning a new tag to a task.

Open Task.swift and add the following method to the Task class:

override func newScriptingObject(of objectClass: AnyClass,
                                 forValueForKey key: String,
                                 withContentsValue contentsValue: Any?,
                                 properties: [String: Any]) -> Any? {

  let tag: Tag = super.newScriptingObject(of: objectClass, forValueForKey: key,
                                          withContentsValue: contentsValue,
                                          properties: properties) as! Tag
  tag.task = self

  return tag

This method is sent to the container of the new object, which why you put it into the Task class and not the Tag class. The call is passed to super to get the new tag, and then the task property is assigned.

Quit and build and run your app. Now run the sample script 6. Tasks With Tags.scpt which lists tag names, lists the tasks with a specified tag, and deletes and create tags.