viewDidAppear called twice, but viewWillAppear called once

Question

I have discovered that when my program starts, in one of my viewcontrollers the order of calling is viewDidAppear, viewWillAppear, viewDidAppear.

I was not expecting the first viewDidAppear to be called. What could be causing this and how do I fix it? ATM I have a flag in viewDiDAppear to check if viewWillAppear was called, but it's a hack.

The stacktrace (which is identical in bot calls to viewDidAppear)is:

#0  0x0000509e in -[MainView viewDidAppear:] at MainView.m:497
#1  0x3097e96e in -[UINavigationController navigationTransitionView:didEndTransition:fromView:toView:]
#2  0x30af3abe in -[UINavigationTransitionView _notifyDelegateTransitionDidStopWithContext:]
#3  0x30af4930 in -[UINavigationTransitionView _navigationTransitionDidStop]
#4  0x3091af0d in -[UIViewAnimationState sendDelegateAnimationDidStop:finished:]
#5  0x3091ba9e in +[UIViewAnimationState popAnimationState]
#6  0x30af46fd in -[UINavigationTransitionView transition:fromView:toView:]
#7  0x30af3b01 in -[UINavigationTransitionView transition:toView:]
#8  0x30979f09 in -[UINavigationController _startDeferredTransitionIfNeeded]
#9  0x30a97d9c in -[UILayoutContainerView layoutSubviews]
#10 0x0040bd94 in -[CALayer layoutSublayers]
#11 0x0040bb55 in CALayerLayoutIfNeeded
#12 0x0040b3ae in CA::Context::commit_transaction
#13 0x0040b022 in CA::Transaction::commit
#14 0x308f942a in -[UIApplication _reportAppLaunchFinished]
#15 0x308fef33 in -[UIApplication handleEvent:withNewEvent:]
#16 0x308fad82 in -[UIApplication sendEvent:]
#17 0x309013e1 in _UIApplicationHandleEvent
#18 0x32046375 in PurpleEventCallback
#19 0x30245560 in CFRunLoopRunSpecific
#20 0x30244628 in CFRunLoopRunInMode
#21 0x308f930d in -[UIApplication _run]
#22 0x309021ee in UIApplicationMain
#23 0x00001e82 in main at main.m:14

Answer 1

Put a break point in viewDidAppear, then inspect the call stack in the debugger. It will tell you what is calling the method.

Answer 2

It's very likely that you want the behavior of viewDidLoad rather than viewDidAppear - viewDidAppear can be called multiple times by your ViewController when you're not expecting it to.

Answer 3

When viewDidAppear is called, can you cancel another viewDidAppear in the event queue by following method ? Sometimes I use this to avoid some methods being called twice or more.

[NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(viewDidAppear) object:nil];