iOS自定义转场动画——自定义模态跳转之Present

Modal

modal转场方式即使用 presentViewController() 方法推出的方式，默认情况下，第二个视图从屏幕下方弹出。下面就来介绍下 modal 方式转场动画的自定义。

present

还是先来看一下完成的效果

准备

1. 创建一个新的工程，删掉Main，在AppDelegate中创建自定义UIWindow，设置rootVC为ViewController。
2. 在ViewController中创建一个全屏的ImageView，并且指定一张图片；新建一个按钮用于present。
3. 新建一个SecondViewController。同样创建一个全屏的ImageView，指定一张和ViewController不同的图片，新建一个同于dismiss的按钮

开始

1. 创建一个文件继承自 NSObject，取名为PresentTransition并在.h中遵守 UIViewControllerAnimatedTransitioning协议。
2. 实现协议的两个方法，并在其中编写 Push 的动画。 具体的动画实现过程都在代码的注释里：

// 返回动画的时间
- (NSTimeInterval)transitionDuration:(nullable id )transitionContext{
    return 0.8;
}
- (void)animateTransition:(id )transitionContext{
    ViewController * fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    SecondViewController * toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIView * container = [transitionContext containerView];
    
    [container addSubview:toVC.view];
    [container bringSubviewToFront:fromVC.view];
    
    // 改变m34
    CATransform3D transfrom = CATransform3DIdentity;
    transfrom.m34 = -0.002;
    container.layer.sublayerTransform = transfrom;
    
    // 设置archPoint和position
    CGRect initalFrame = [transitionContext initialFrameForViewController:fromVC];
    toVC.view.frame = initalFrame;
    fromVC.view.frame = initalFrame;
    fromVC.view.layer.anchorPoint = CGPointMake(0, 0.5);
    fromVC.view.layer.position = CGPointMake(0, initalFrame.size.height / 2.0);
    
    // 添加阴影效果
    CAGradientLayer * shadowLayer = [[CAGradientLayer alloc] init];
    shadowLayer.colors =@[
                         [UIColor colorWithWhite:0 alpha:1],
                         [UIColor colorWithWhite:0 alpha:0.5],
                         [UIColor colorWithWhite:1 alpha:0.5]
                         ];
    shadowLayer.startPoint = CGPointMake(0, 0.5);
    shadowLayer.endPoint = CGPointMake(1, 0.5);
    shadowLayer.frame = initalFrame;
    
    UIView * shadow = [[UIView alloc] initWithFrame:initalFrame];
    shadow.backgroundColor = [UIColor clearColor];
    [shadow.layer addSublayer:shadowLayer];
    [fromVC.view addSubview:shadow];
    shadow.alpha = 0;
    
    // 动画
    [UIView animateKeyframesWithDuration:[self transitionDuration:transitionContext] delay:0 options:2 animations:^{
        fromVC.view.layer.transform = CATransform3DMakeRotation(-M_PI_2, 0, 1, 0);
        shadow.alpha = 1.0;
    } completion:^(BOOL finished) {
        fromVC.view.layer.anchorPoint = CGPointMake(0.5, 0.5);
        fromVC.view.layer.position = CGPointMake(CGRectGetMidX(initalFrame), CGRectGetMidY(initalFrame));
        fromVC.view.layer.transform = CATransform3DIdentity;
        [shadow removeFromSuperview];
        
        [transitionContext completeTransition:YES];
    }];
}

使用动画

1. 让 FirstViewController 遵守 UIViewControllerTransitioningDelegate 协议，并将 self.transitioningDelegate 设置为 self。

self.transitioningDelegate = self;

2. 实现 UIViewControllerTransitioningDelegate 协议的两个方法，用来指定动画类。

// present动画
-(id)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source{
    return [[PresentTransition alloc] init];
}

3. 在present按钮的点击方法中，必须把SecondViewController的transitioningDelegate也设置为self，让ViewController管理SecondViewController的动画

-(void)presentClick{
    SecondViewController * secondVC = [[SecondViewController alloc] init];
    secondVC.transitioningDelegate = self; // 必须second同样设置delegate才有动画
    [self presentViewController:secondVC animated:YES completion:^{
    }];
}