iOS: Save images in App Group for use on Apple Watch

Question

Background:

In my iPhone app I retrieve images and save them to the documents directory for quicker loading. I know that to use these images on the Apple Watch, I must share them with an App Group.

So, I create an App Group, updated my provisioning profile, all that jazz. Now my problem is that I do not know how to save an image to the App Group and read that image within my WatchKit files.

Here is what I have tried for saving the image to the App Group:

NSString *container = @"group.com.appName.watchdatasharing";

NSUserDefaults *defaults = [[NSUserDefaults alloc] initWithSuiteName:container];

[defaults setValue:UIImagePNGRepresentation([FileManager readImageFromFileWithName:@"icon1_imgUrl"]) forKey:@"icon1_imgUrl"];

• note: my FileManager class returns a UIImage

And to retrieve the image in my WatchKit app, I use this code:

NSString *container = @"group.com.fantrac.watchdatasharing";

NSUserDefaults *defaults = [[NSUserDefaults alloc] initWithSuiteName:container];

NSData* imageData = [defaults valueForKey:@"icon1_imgUrl"];
UIImage* image = [UIImage imageWithData:imageData];

[tableRow.iconImage setImage:image];

Question:

There is not image showing when I test on the Apple Watch. What do I need to do differently to save/ retrieve the images between my app and Apple Watch?

Answer 1

If you use watchOS 2, you can use WatchConnectivity. I attach a sample code for your reference.

on iPhone:

// Create a Watch Connectivity session
- (void)viewDidLoad
{
    [super viewDidLoad];

    self.applicationDict = @{@"foo" : @"bar"};

    if ([WCSession isSupported]) {
        WCSession *session = [WCSession defaultSession];
        session.delegate = self;
        [session activateSession];
    }
}

// Transfer file to Apple Watch 
- (IBAction)fileTransferButtonTapped:(id)sender
{
    // File Transfer
    NSURL *url = 
    [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"sample" ofType:@"png"]];
    WCSessionFileTransfer *fileTransfer = 
    [[WCSession defaultSession] transferFile:url
                                    metadata:self.applicationDict];
}

on Watch:

// Receive file from iPhone
- (void)session:(nonnull WCSession *)session didReceiveFile:(nonnull WCSessionFile *)file
{
    // recieve file
}

ref. http://www.kristinathai.com/watchos-2-how-to-communicate-between-devices-using-watch-connectivity/