Having spent the last few weekends creating a web site to market and support my App Tubulate, then spending the next two weekends getting it on the AppStore. It’s time for the next step, Watch integration! (Programming: Good - PhotoShop: Meh).

The first challenge to surmount is how to ship data from the iPhone App to the WatchKit extension. Data access needs to go through the phone App as it has all of the infrastructure to perform the REST calls already written and tested.

There are a couple of approaches to data transfer available:

You can set up a shared group and use an NSUserdefaults object to synchronize data between the two App parts. This approach is useful but not exactly what I need.

A second approach is to invoke the WKInterfaceController.openParentApplication method in the extension which leads to the handleWatchKitExtensionRequest method on the iPhone App’s AppDelegate to be invoked. This method can perform arbitrary calculations and return data to the watch via an NSDictionary of string value pairs.

The Objective-C definition of the handleWatchKitExtensionRequest method is as follows

-(void)application:(UIApplication *)application handleWatchKitExtensionRequest:(NSDictionary *)userInfo reply:(void (^)(NSDictionary *))reply{
    HomePageDataCollector *s = [[HomePageDataCollector alloc] init];
    [s collect:^(HomePageData *data) {
        reply([data toWatchKit]);
    }];
}

The parameter userInfo is a dictionary used to pass parameters in from the watch. There is only one entry point to the application from the phone so we will need to pass in an descriptor for the operation to perform and then dispatch execution to the correct class. Here we hard wire the call to the HomePageDataCollector class and pass the data back to the watch via the reply() callback.

As I mentioned the code is execute in a block, my REST calls are asynchronous, unless I can somehow chain the invocations then the call will terminate and I will be up a famous creek without a paddle.

I’ll cover the REST chain in the next post.