### 【问题】
使用IOS9之前的SDK，转屏会有几个函数会被响应。
1.转屏前回调函数
- (void)willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)durationNS_DEPRECATED_IOS(3_0,8_0,"Implement viewWillTransitionToSize:withTransitionCoordinator: instead")__TVOS_PROHIBITED;
2.转屏后回调函数
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientationNS_DEPRECATED_IOS(2_0,8_0)__TVOS_PROHIBITED;
可是在IOS9的SDK中不能再使用了，那我们该如何处理呢？
### 【分析】
根据帮助文档的信息，让我们改用下面这个函数
- (void)viewWillTransitionToSize:([CGSize](https://developer.apple.com/library/ios/documentation/GraphicsImaging/Reference/CGGeometry/index.html#//apple_ref/doc/c_ref/CGSize))`size
` withTransitionCoordinator:(id<[UIViewControllerTransitionCoordinator](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewControllerTransitionCoordinator_Protocol/index.html#//apple_ref/occ/intf/UIViewControllerTransitionCoordinator)>)`coordinator;`
可是怎么区分转屏前后呢？
我们看到第二个参数coordinator，它的类型是[UIViewControllerTransitionCoordinator](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewControllerTransitionCoordinator_Protocol/index.html#//apple_ref/occ/intf/UIViewControllerTransitionCoordinator)，它能响应VC转换进度，并且提供了以下方法：
- (BOOL)animateAlongsideTransition:(void (^)(id<[UIViewControllerTransitionCoordinatorContext](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewControllerTransitionCoordinatorContext_Protocol/index.html#//apple_ref/occ/intf/UIViewControllerTransitionCoordinatorContext)> context))`animation
` completion:(void (^)(id<[UIViewControllerTransitionCoordinatorContext](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewControllerTransitionCoordinatorContext_Protocol/index.html#//apple_ref/occ/intf/UIViewControllerTransitionCoordinatorContext)> context))`completion;`
### 【解决方法】
~~~
- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id <UIViewControllerTransitionCoordinator>)coordinator
{
[coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context)
{
NSLog(@"转屏前调入");
} completion:^(id<UIViewControllerTransitionCoordinatorContext> context)
{
NSLog(@"转屏后调入");
}];
[super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
}
~~~
