Swiftpack.co - Package - elegantchaos/Actions


An abstraction for action-handling, for Swift/AppKit-based applications.


Note that the API is in flux currently.

Although I'm using semantic version numbers, I will abuse them until things settle down - so new maintenance releases are likely to contain breaking changes for a while. This is simply to avoid prematurely ending up at version 10.x!



Make an ActionManager, attach it to something global (eg your app delegate), and register some actions with it.

If you're going to bind UI items to it, hook it into the responder chain:

class Application: NSObject, NSApplicationDelegate {
let actionManager = ActionManager()

func applicationWillFinishLaunching(_ notification: Notification) {
        MyAction(identifier: "MyAction"),
        AnotherAction(identifier: "AnotherAction")

    actionManager.nextResponder = NSApp.nextResponder
    NSApp.nextResponder = actionManager


Set the action of user interface objects to performAction(_ sender: Any), and the target to the first responder. Set the identifier of the UI item to the identifier of the action you want to invoke.

Alternatively, invoke an action directly with actionManager.perform("MyAction").


Actions are classes.

To define an action, inherit from Action, and implement perform:

class MyAction: PersonAction {
    override func perform(context: ActionContext) {
        // do stuff here


The context passed to perform contains the original sender.

It also contains a dictionary of other information. Items in the responder chain can add items to this dictionary whenever actions are performed, by implementing the ActionContextProvider protocol.

This lets a view controller or window controller pass essential information to actions whilst keeping them fully decoupled.

The context also contains a parameters array. Parameters are parsed out of the identifier that was used to invoke the action.

The algorithm for parsing the identifier is:

  • split it into a list of strings separated by '.'
  • pop items from the left of the list until we find one that matches a registered action
  • everything unused to the right of the list becomes the context parameters

This allows you to bind multiple user interface items to the same action, in a parameterised way.

For example you can set a button's identifier to button.MyAction and a menu item's to menu.MyAction. Both will have unique identifiers - which Xcode insists on - but both will be resolved to the MyAction action.

In another example, you could set two button identifiers to MyAction.red and MyAction.blue. Both will invoke MyAction, but the context.parameters array will contain ["red"] for the first one, and ["blue"] for the second. The action can read this parameter and behave differently in either case.


Actions are often only valid in certain situations - for example when some text is selected.

To perform validation, override the validate(context: ActionContext) -> Bool and examine the context that's passed in.

Action Observers

If your user interface wants to know when certain actions have been performed, this pattern may be useful.

Define a protocol for observers of your action(s). This can contain anything you need.

Implement your protocol in the user interface controllers that want to observe. Also implement the ActionContextProvider protocol, and append the controller to a key that the action(s) will read:

protocol MyActionObserver {
  func myMethod(myArgument: String)

extension MyViewController: ActionContextProvider, MyActionObserver {

func provide(context: ActionContext) {
    context.append(key: "MyActionObserver", value: self)

In the action, as well as perfoming the actual work, enumerate the observer key. For each observer, call a method from your protocol, passing any arguments or context that is relevant:

class MyAction: PersonAction {
    override func perform(context: ActionContext) {
        // do some stuff here
        // notify observers
        context.forEach(key: "MyActionObserver") { (observer: MyActionObserver) in
            observer.myMethod(myArgument: "myValue")


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v1.0.3 - Sep 7, 2018

Added support for item validation.

v1.0.2 - Sep 7, 2018

A few tweaks to the API. Added direct support for appending to, and enumerating over context info items that are lists.

v1.0.1 - Sep 6, 2018

Integrated with Travis. Added tests.

v1.0.0 - Sep 6, 2018

Initial version. Just has basic context gathering and action performing.