Measurement Events: NSNotification as Event for Tracking

Usage

Post a measurement event.

[AQSEvent postEvent:@"event_name" args:@{
    @"key": @"value"
}];

Observe measurement events.

self.observer = [AQSEvent observeWithBlock:^(NSString *eventName, NSDictionary *eventArgs) {
    // Do something with arguments.
    //
    // Typically perform actual tracking events in this block.
}];

Protocol

A measurement event is an NSNotification that conforms to following protocol.

1. Event's notification name should be always same.
2. Event's notification should contain an userInfo that contains following values
   1. The userInfo should contain event name as NSString.
   2. The userInfo should contain event parameters as NSDictionary<NSString, id>.

Advantage?

Testing method invocation is typically hard

Testing invocation of [Analytics trackSomething] in a method is nearly impossible.

Taking an analytics instance as initialization arguments? Nonsense.

There's no accepted way to post Events with unified format

iOS posts numerous number of NSNotifications that notifies App Life Cycle Event and iCloud Event and ...

Also 3rd pirty libraries do so.

However there are too many NSNotification name and userInfo format. To use them for tracking events, we have to find which NSNotification are there, write a lot of NSNotification observers and parsing and re-formatting userInfo for each formats.

Measurement Events might be The Holy Grail

1. It is NSNotification based - It means you can test it with Expecta's notify()
2. You only have to track NSNotification whose name is kAQSEvent. Only one observer. You only need to send the args to your analytics tracking code. (As most of analytics provides tracking an event with name and a dictionary params.)

And this is just an NSNotification. No magicically things. Easy to understand.

Implementation

AQSEvent provide a helper to post / subscribe Events.

Posting an Event

[AQSEvent postEvent:@"location/changed" args:@{
    @"latitude": @(40.712784),
    @"longitude": @(-74.005941)
}];

This is a shorthand for following code.

[[NSNotificationCenter defaultCenter] postNotification:kAQSEvent object:nil userInfo:@{
    kAQSEventName: @"location/changed",
    kAQSEventArgs: @{
        @"latitude": @(40.712784),
        @"longitude": @(-74.005941)
    };
}];

Subscribing Events

Subscribe to events are also easy.

AQSEvent provides a helper.

@property (nonatomic, strong) AQSEventObserver *eventObserver;

// Then in @implementation,

self.eventObserver = [AQSEvent observeWithBlock:^(NSString *eventName, NSDictionary *eventArgs) {
    // Do something
}];

This is a shorthand for following code.

[[NSNotificationCenter defaultCenter] addObserver:kAQSEvent selector:@selector(subscribeEvent:) object:nil];

AQSEventObserver automatically does - removeObserver: on - dealloc. No more memory leak as long as you use AQSEvent to observe events.

Testing Events

Assume you want to test that following method posts an Event for tracking.

[someObject doSomething];

XCTestExpectation helps you testing measurement events. And AQSEvent provides a helper category for easier testing.

- (void)testItPostsSomeMeasurementEvent {
    XCTestExpectation *expectation = [self expectationForNotification:kAQSEvent object:nil handler:BOOL^(NSNotification *notification) {
        [expectation fulfill];

        return [notification aqs_isEqualToMeasurementEvent:@"event_name" args:@{@"key": @"value"}];
    }];

    [someObject doSomething]; // Assume it posts "event_name" event with {"key": "value"}

    [self waitForExpectationWithTimeout:1.0 handler:nil];
}

Installation

pod "AQSEvent"

Related Projects

• AQSEventAggregator - Aggregates measurement events.