iOS8的UIPresentationController

从iOS8开始，controller之间的跳转特效，需要用新的API UIPresentationController来实现。比如希望实现这样一个特效：显示一个模态窗口，大小和位置是自定义的，遮罩在原来的页面上。在iOS8之前，可以在viewWillAppear里设置superview的frame：

Objc代码

1. 1. 
      
2. - (void)presentModal:(NSDictionary*)result
3. {
4. YLSCheckoutSignatureController *controller = [[YLSCheckoutSignatureController alloc] initWithModel:result];
5. 
   
6. if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0) {
7. controller.modalPresentationStyle = UIModalPresentationCustom;
8. }else{
9. controller.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
10. controller.modalPresentationStyle = UIModalPresentationFormSheet;
11. }
12. 
    
13. [self presentViewController:controller animated:YES completion:nil];
14. }
    1. 
       

Objc代码

1. 1. 
      
2. -(void) viewWillAppear:(BOOL)animated
3. {
4. // in iOS8, handle by UIPresentationController
5. if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0) {
6. return;
7. }
8. 
   
9. self.view.superview.layer.cornerRadius = 10;
10. self.view.superview.layer.borderColor = [UIColor darkGrayColor].CGColor;
11. self.view.superview.clipsToBounds = YES;
12. self.view.superview.frame = CGRectMake(62, 114, 900, 540);
13. }
    1. 
       

但是以上的代码，在iOS8里就不再生效了，要用UIPresentationController来实现

首先明确一点，从Controller A->B，B的样式和跳转特效，还是由B来控制的。只不过以前是直接在Controller的生命周期方法里操作，而现在有专门的API来完成而已。这种设计也是合理的，否则如果从A可以跳转到B和C，但是样式和特效不一样，就只能通过在A里面设置实例变量来区分了，容易出错也很别扭。所以把跳转的行为由目标Controller来控制是很合理的

不过这组API的文档不太全，后续SDK升级可能会逐渐完善。以下介绍实现步骤：

目标Controller实现特定protocol

首先目标Controller要实现特定的协议，创建一个UIPresentationController

Objc代码

1. 1. 
      
2. @interface YLSCheckoutSignatureController : UIViewController<UIScrollViewDelegate, UIViewControllerTransitioningDelegate>
   1. 
      

Objc代码

1. 1. 
      
2. self.transitioningDelegate = self;
   1. 
      

Objc代码

1. 1. 
      
2. - (UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(UIViewController *)presenting sourceViewController:(UIViewController *)source
3. {
4. return [[YLSMainPresentationController alloc] initWithPresentedViewController:presented presentingViewController:presenting];
5. }
   1. 
      

当条件满足时，iOS系统会调用这个方法，于是可以实例化自定义的UIPresentationController子类，定义跳转的样式和特效

自定义UIPresentationController

然后就要实现自定义的UIPresentationController，下面这段实例代码，实现居中展示一个自定义frame的模态页面，同时有半透明背景遮住原来的页面

Objc代码

1. 1. 
      
2. @implementation YLSMainPresentationController
3. 
   
4. {
5. UIView *dimmingView;
6. }
7. 
   
8. -(id) initWithPresentedViewController:(UIViewController *)presentedViewController presentingViewController:(UIViewController *)presentingViewController
9. {
10. self = [super initWithPresentedViewController:presentedViewController presentingViewController:presentingViewController];
11. if(self){
12. 
    
13. dimmingView = [[UIView alloc] init];
14. dimmingView.backgroundColor = [UIColor grayColor];
15. dimmingView.alpha = 0.0;
16. }
17. return self;
18. }
19. 
    
20. - (void)presentationTransitionWillBegin
21. {
22. dimmingView.frame = self.containerView.bounds;
23. [self.containerView addSubview:dimmingView];
24. [self.containerView addSubview:self.presentedView];
25. 
    
26. id<UIViewControllerTransitionCoordinator> coordinator = self.presentingViewController.transitionCoordinator;
27. 
    
28. [coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context) {
29. dimmingView.alpha = 0.5;
30. } completion:nil];
31. }
32. 
    
33. - (void)presentationTransitionDidEnd:(BOOL)completed
34. {
35. if(!completed){
36. [dimmingView removeFromSuperview];
37. }
38. }
39. 
    
40. - (void)dismissalTransitionWillBegin
41. {
42. id<UIViewControllerTransitionCoordinator> coordinator = self.presentingViewController.transitionCoordinator;
43. 
    
44. [coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context) {
45. dimmingView.alpha = 0.0;
46. } completion:nil];
47. }
48. 
    
49. - (void)dismissalTransitionDidEnd:(BOOL)completed
50. {
51. if(completed){
52. [dimmingView removeFromSuperview];
53. }
54. }
55. 
    
56. - (CGRect)frameOfPresentedViewInContainerView
57. {
58. return CGRectMake(62.f, 114.f, 900.f, 540.f);
59. }
60. 
    
61. @end
    1. 
       

代码确实比以前复杂了一点，但是其实每个生命周期方法都是比较明确的，开发者可控的粒度也更细了。比如设置presented frame，就有专门的方法，只要返回CGRect就可以了，还是比较方便的

原始的ViewController发起跳转动作

经过前面2步，当自定义跳转发生时，就可以很细致地控制样式和跳转行为。接下来就是由原始controller（presenting view controller）来发起跳转动作：

Objc代码

1. 1. 
      
2. - (void)presentModal:(NSDictionary*)result
3. {
4. YLSCheckoutSignatureController *controller = [[YLSCheckoutSignatureController alloc] initWithModel:result];
5. 
   
6. if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0) {
7. controller.modalPresentationStyle = UIModalPresentationCustom;
8. }else{
9. controller.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
10. controller.modalPresentationStyle = UIModalPresentationFormSheet;
11. }
12. 
    
13. [self presentViewController:controller animated:YES completion:nil];
14. }
    1. 
       

关键是设置modalPresentationStyle为UIModalPresentationCustom，然后当presentViewController方法调用时，iOS系统就会创建出UIPresentationController的实例，来控制跳转的行为