UIDeviceOrientationDidChangeNotification calling multiple times - ios

Question

UIDeviceOrientationDidChangeNotification is calling multiple times when the device changes orientation. I am unsure why this happens or how to fix it.
What I am trying to do is to keep the contentoffset of the scrollview the same, so when the user rotates the screen the app keeps the page they were on.
The odd thing is when I rotate the screen the first time the code executes like I would want. But every time after that the code executes multiple times and eventually the contentoffset is set o 0.
Here's what I have.
- (void)loadView {
//some code that sizes itself depending on the current orientation
//WILL BE CALLED AFTER EVERY ORIENTATION CHANGE
}
- (void)viewDidLoad {
//begin generating messages
[[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
[[NSNotificationCenter defaultCenter]
addObserver:self selector:#selector(orientationChanged:)
name:UIDeviceOrientationDidChangeNotification
object:[UIDevice currentDevice]];
//if is portrait and was landscape
if (orientation==1 && temp==2) {
int cal = offsetHolder.x/screenframe.size.height;
offsetHolder.x = cal * screenframe.size.width;
ScrollView.contentOffset = offsetHolder;
}
//if is landscape and was portrait
if (orientation==2 && temp==1) {
int cal = offsetHolder.x/screenframe.size.width;
offsetHolder.x = cal * screenframe.size.height;
ScrollView.contentOffset = offsetHolder;
}
}
On orientation change I change the value of 'int orientation' then call loadview to change the sizing of the view. Then I call viewdidload to get the proper contentoffset
- (void) orientationChanged:(NSNotification *)note {
CGRect screenframe = [[UIScreen mainScreen] bounds];
//holding the current offset
offsetHolder = ScrollView.contentOffset;
if ([[UIDevice currentDevice] orientation] == 1 || [[UIDevice currentDevice] orientation] == 0 || [[UIDevice currentDevice] orientation] == UIDeviceOrientationPortraitUpsideDown) {
temp=orientation;
orientation = 1;
[self loadView];
[self viewDidLoad];
}
else if ([[UIDevice currentDevice] orientation] == UIDeviceOrientationFaceDown || [[UIDevice currentDevice] orientation] == UIDeviceOrientationFaceUp){
temp=orientation;
}
else{
temp=orientation;
orientation = 2;
[self loadView];
[self viewDidLoad];
}
}
EDIT:
I have found the problem. What I am doing is creating another instance of self.view instead of overwriting this one. Is there an easy way to destroy this view and re-initialize it?
EDIT2:
Have found a fix. I stopped calling loadview and viewdidload as per jsds' instructions. And instead moved all code in my loadview to another function that I called from loadview. All this code does is instantiate the UI (initview) objects and places them in the correct places depending upon orientation.
Then I create another function that removes all subviews from the view. Then on orientation change I call this function and my initview to destroy all subviews and then recreate them on orientation change.

Answer 1

UIDeviceOrientation basically has 6 different states, namely two portrait, two landscape, and face up and face down. So lets say when you pick up your device from flat position to vertical position, the notification will be triggered.
You can filter the faceup, facedown, and unknown states by using the macro UIDeviceOrientationIsValidInterfaceOrientation
UIDeviceOrientation currentOrientation = [[UIDevice currentDevice] orientation];
// Ignore changes in device orientation if unknown, face up, or face down.
if (!UIDeviceOrientationIsValidInterfaceOrientation(currentOrientation)) {
return;
}
If you still find the notification getting triggered multiple times, I am afraid you may need to use your custom logic with flags to check the previous and current value.
In my case, since I use reactive cocoa framework, the following code works for me :
if (IS_IPAD) {
#weakify(self);
[[[[[[[NSNotificationCenter defaultCenter] rac_addObserverForName:UIDeviceOrientationDidChangeNotification object:nil]
takeUntil:[self rac_willDeallocSignal]]
map:^id (NSNotification *notification) {
return #([[UIDevice currentDevice] orientation]);
}]
filter:^BOOL(NSNumber *deviceOrientationNumber) {
UIDeviceOrientation currentOrientation = [deviceOrientationNumber integerValue];
//We ignore the UIDeviceOrientationUnknown, UIDeviceOrientationFaceUp and UIDeviceOrientationFaceDown
return UIDeviceOrientationIsValidInterfaceOrientation(currentOrientation);
}]
distinctUntilChanged]
subscribeNext:^(id x) {
#strongify(self);
//do something here...
}];
}
Here the distinctUntilChanged method makes sure the code gets triggered only when the orientation changes to a new valid value.

Answer 2

You should never call loadView or viewDidLoad yourself. That's up to the framework to manage.
If you are positioning or resizing views based on the view bounds in viewDidLoad, don't. Move that to viewWillLayoutSubviews. That will be called automatically when the device orientation changes.
Alternatively, use autolayout constraints and then you won't have to do anything at all.