iOS弹框优化

简介

ios中present controller之后，上一层的controller的内容是不可见的，但是有的弹框需要能看到上一层的内容，这时候我们就要重写present的动画效果，然后手动的改变present动作。

UIViewControllerTransitioningDelegate

这个代理主要是改变一些系统的自定义动画，其中有一个- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source方法，这个方法会返回一个动画效果，也就是present这个动作的动画效果，如果不重写，会自动用系统的。
重写方法的实现：

- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source {
    //这里面AnimatedTransitioning是自己自定义实现的动画效果
    AnimatedTransitioning *controller = [[AnimatedTransitioning alloc]init];
    controller.isPresenting = YES;
    return controller;
}

再看看AnimatedTransitioning的实现：

@protocol AnimatedTransitioningProtocol <NSObject>
- (void)startAnimation;
@end

@interface AnimatedTransitioning : NSObject <UIViewControllerAnimatedTransitioning>
@property (nonatomic, assign) BOOL isPresenting;
@end

#import "AnimatedTransitioning.h"
@implementation AnimatedTransitioning
//===================================================================
// - UIViewControllerAnimatedTransitioning
//===================================================================
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext {
    return 0.25f;
}

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
    //获取当前发出present动作的controller的View
    UIView *inView = [transitionContext containerView];
    //获取到将要present的controller
    UIViewController<AnimatedTransitioningProtocol> *toVC = (UIViewController<AnimatedTransitioningProtocol> *)[transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    //获取到发出present动作的controller
    UIViewController *fromVC = (UIViewController *)[transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    //讲要去的VC的view添加到触发present动作的VC上面，这样上一层的VC的内容就不会消失了
    [inView addSubview:toVC.view];
    //设置要present VC的view的frame
    [toVC.view setFrame:CGRectMake(0, 0, fromVC.view.frame.size.width, fromVC.view.frame.size.height)];
    //这时候调用自定义的一个代理，手动的写弹框vc上面内容的动画
    [toVC startAnimation];
    //注意这个一定要设置，如果没有使用，系统会不知道当前的transition是否已经结束，这样造成的后果:使app进入某种未知状态，比如presentingViewController能看到新view但是无法和用户交互。
    [transitionContext completeTransition:YES];
}
@end

有待改进，如有错误，还请大神指正。