Lauching App with URL (via UIApplicationDelegate's handleOpenURL) working under iOS 4, but not under iOS 3.2

Christian Fries picture Christian Fries · Aug 31, 2010 · Viewed 23.8k times · Source

I have implemented UIApplicationDelegate's

application:didFinishLaunchingWithOptions:

and

application:handleOpenURL:

according to specification, i.e.,

application:didFinishLaunchingWithOptions:
returns YES 

and

application:handleOpenURL: opens the URL. 

The code works under iOS 4 (in both cases, i.e., when the app is launched and when it becomes active from suspended state). However, the code does not work under iOS 3.2.

Answer

Christian Fries picture Christian Fries · Aug 31, 2010

I give an answer to my own question. Finding out the solution took me a while and was quite frustrating. If you do an internet search you find some partial answers, but it still took me a while to work out the following solution and I do hope it adds some clarity.

So first, the recommended behavior of your app appears to be the following (see Opening Supported File Types in iOS Ref Lib):

  • Do not implement applicationDidFinishLaunching: (see the note at UIApplicationDelegate).
  • Implement application:didFinishLaunchingWithOptions: and check the URL, return YES if you can open it, otherwise NO, but do not open it.
  • Implement application:handleOpenURL: and open the URL, return YES if successful, otherwise NO.

In iOS 4, passing an URL to an app results in one of the following two behaviors:

  • If the app is launched then application:didFinishLaunchingWithOptions: is called and application:handleOpenURL: is called if and application:didFinishLaunchingWithOptions: returned YES.
  • If the app is becoming active from suspended state then application:didFinishLaunchingWithOptions: is not called but application:handleOpenURL: is called.

However, in iOS 3.2 it appears as if application:handleOpenURL: is never called! A hint that the behavior is different under iOS 3.2 can be found in Handling URL Requests. There you find that application:handleOpenURL: is called if application:didFinishLaunchingWithOptions: is not implemented, but applicationDidFinishLaunching: is implemented. But application:handleOpenURL: is not called if application:didFinishLaunchingWithOptions: is implemented.

Hence, one solution to make the code work under 3.2 and 4.0 is:

  • Open the URL in application:didFinishLaunchingWithOptions:, but then return NO to prevent that application:handleOpenURL: is called.
  • Open the URL in application:handleOpenURL:, in case you are under 4.0 and the app was in suspended state.

I found this solution in another post, but I was confused, because it contradicted the recommendation in iOS Ref Lib documentation (namely that we should return YES in application:didFinishLaunchingWithOptions:). (At that point I did not realize that the documentation contradicts it self).

I believe that the current iOS 4.0 behavior will be the future behavior I prefer the following solution:

  • Do not implement applicationDidFinishLaunching:.
  • Implement application:didFinishLaunchingWithOptions: and check the URL, return YES if you can open it, otherwise NO, but do not open it. If we are on 3.2, open the URL.
  • Implement application:handleOpenURL: and open the URL, return YES if successful, otherwise NO.

So in summary, I implement the iOS 4 behavior and added the following line to application:didFinishLaunchingWithOptions:

    if([[[UIDevice currentDevice] systemVersion] hasPrefix:@"3.2"]) {
        [self application:application handleOpenURL:url];
    }

which make the code work under 3.2.