How to identify that an UIViewController is presented
I have created an UIViewController sub class which can either be pushed in a navigation stack of a UINavigationController or presented(modally) from any UIViewController. I need to identify whether my view controller is presented, if it is presented I need to add a toolbar with a close button at the top of the view controller. (else if it is pushed in navigation stack then the default close button will get added, by using that the user can go back.)
In all the available versions say 4.3, 5.0, till 6.0, from inside an UIViewController sub class, Can I assume that the view controller is presented(modally) if the following condition is satisfied.
if(self.parentViewController == nil || self.navigationController == nil)
Answer
With iOS 5, UIViewController gained a readonly property named presentingViewController, that replaces the older semantics of parentViewController (which now describes containment). This property can be used when a view controller needs to get at the view controller that’s presenting it — note: this will often be something else than what you’d expect, if you’re new to the API!
In addition, the isBeingPresented property had been introduced to pretty much solve the class of situations you’re currently in. Check for this property in your view controller’s viewWillAppear:.
Update
I overread that you seem to target iOS 4.3 as well:
In that case, you need to guard the call to isBeingPresented with an if ([self respondsToSelector:…]) you can then in the else block check for whether the parentViewController is not nil.
Another approach to backwards compatibility might be to override +resolveInstanceMethod: to add an implementation for -isBeingPresented at runtime. This will leave your calling sites clean, and you’d get rid of runtime-magic as soon as you let go of ancient iOS support ;-)
Note, though, that there are edge cases to this, and you initial approach as well, when running on iOS <5:
The view controller can be presented contained in any other view controller—including navigation controllers. When that last case happens, you’re out of luck: parentViewController will be nil, while navigationController will not. You can try to add gobs of unwieldy code to mitigate this limitation in older iOSes…or you could just let it go.