Warning: passing incompatible type to setRootViewController:

I am doing a calculator for the iPhone, where on rotation of the device, a new view is displayed, and I am getting the following three errors:

CalculatorAppDelegate.m:21: warning: incompatible Objective-C types 'struct CalculatorViewController *', expected 'struct UIViewController *' when passing argument 1 of 'setRootViewController:' from distinct Objective-C type`

this error (and below) is from code:

self.window.ro开发者_运维百科otViewController = self.viewController;

CalculatorAppDelegate.m: warning: Semantic Issue: Incompatible pointer types assigning to 'UIViewController *' from 'CalculatorViewController *'

the below error is from:

UIInterfaceOrientation interfaceOrientation = [[object object] orientation];`

CalculatorViewController.m: warning: Semantic Issue: Implicit conversion from enumeration type 'UIDeviceOrientation' to different enumeration type 'UIInterfaceOrientation'

For your first 2 errors:

• Either CalculatorViewController is not declared as a subclass of UIViewController in your .h file
• Or the compiler doesn't know about it, because you forgot the #import "CalculatorViewController.h" in your code to let the compiler know about its definition

For your last issue, this is because you misuse UIDeviceOrientation and UIInterfaceOrientation, which are not the same type (even quite related).

• UIInterfaceOrientation define the orientation of the user interface. It only has 4 values: Portrait, Landscape Left, Landscape Right or UpsideDown.
• UIDeviceOrientation define the orientation of the device. It has 6 values, defining that your device is straight up, turns 90° left or right, upsidedown, or faceing down ou up.

If you setup your interface so that it does not rotate (shouldAutorotateToInterfaceOrientation: returns YES only for one of the 4 UIInterfaceOrientation), your UIDeviceOrientation can still change (nothing prevent the user to turn his/her iPhone into any position), but your UIInterfaceOrientation won't change.

If you setup your interface so this it does rotate (shouldAutorotateToInterfaceOrientation: always returns YES), when the user turns his/her iPhone to the right, UIDeviceOrientation will be UIDeviceOrientationLandscapeRight because the iPhone will be turned right... and UIInterfaceOrientation will be UIInterfaceOrientationLandscapeLeft, because the interface orientation will be rotated 90° to the left, so that because the device is turned to the right, the interface will still be displayed horizontally to the user.

You can notice that UIInterfaceOrientation and UIDeviceOrientation have opposed values (for enums that are common to both; of course for UIDeviceOrientationFaceUp and UIDeviceOrientationFaceDown there is no corresponding UIInterfaceOrientation)