Question

I know that if map a url with from:toViewController:, then open that url will create a new view controller and if from:toSharedViewController is used then a shared instance will be used.

But for example

 [map from:@"tt://tabbar/(initWithString:)" toSharedViewController:[MyTabbarController class]];
 TTOpenURL(@"tt://tabbar/string");

This will invoke something similar to

 [[MyTabbarController alloc] initWithString:@"string"]

But what will be happened if TTOpenURL(@"tt://tabbar/somethingelse") in called later?
Since a shared object is used so will the initWithString: be called twice on a same instance?

Answer 1

The answer is : no. I.e., init will not be called on an already initialized instance, but a new instance will be allocated and initialized.

This is due to Three20 associating the object to its full URL, which in your case is either “tt://tabbar/string” or “tt://tabbar/somethingelse”, so that when querying the TTURLMap, no already existing object will be found and a new one will be instantiated. At least, this is true as of Three20 1.0.3. But I guess they have not changed this.

In my opinion, the shared controller mechanism is to be used in very specific cases, like for a setting view, and it should not be thought as a sort of Three20-implemented singleton. Each time I tried to rely on this for more “clever” usage of the TTURLMap, I found myself going back to a non shared controller.