UIViewControllerAnimatedTransitioning是iOS系統提供的轉場動畫協議，遵循該協議可自定義轉場動畫。

系統模態一個控制器時提供了模態風格的屬性

模態風格屬性

模態風格枚舉

分別是從底部滑入，水平翻轉進入，交叉溶解以及翻頁這四種風格，不受iPhone和iPad限制。

接手了一個需求是以push動畫present一個控制器，系統提供的風格并不滿足要求，只能動手改造轉場動畫。

忽略我的丑字。嘿。

自定義轉場動畫流程

過程：

1.控制A present控制器B
2.生成遵循UIViewControllerTransitioningDelegate協議的自定義TransitioningDelegate，將 A.transitioningDelegate = 自定義transitioningdelegate
3.自定義transitioningdelegate生成自定義animatedTransitioning
4.自定義animatedTransitioning遵循UIViewControllerAnimatedTransitioning協議，實現兩個必要方法動畫時長及核心動畫。

話不多說，上代碼

1.自定義轉場動畫代理

自定義transitioningdelegate

自定義transitioningdelegate.h 暴露了transitioningdelegate生成自定義animatedTransitioning的方法， targetEdge屬性用來指定轉場動畫方向，可選UIRectEdgeTop，UIRectEdgeBottom，UIRectEdgeLeft，UIRectEdgeRight。用present實現push效果時使用UIRectEdgeRight。

自定義transitioningdelegate

使用自定義transitioningdelegate生成遵循轉場動畫協議的自定義類

2.實現轉場動畫核心動畫方法

動畫時長

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext
{
    //源控制器
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    //目標控制器
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    // Present:
    //      fromView = The presenting view.
    //      toView   = The presented view.
    // Dismiss:
    //      fromView = The presented view.
    //      toView   = The presenting view.
    
    //容器視圖
    UIView *containerView = transitionContext.containerView;
    
    UIView *fromView = nil;
    UIView *toView = nil;
    
    if ([transitionContext respondsToSelector:@selector(viewForKey:)])
    {
        //iOS8之后
        fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
        toView = [transitionContext viewForKey:UITransitionContextToViewKey];
    }
    else
    {
        //iOS7
        fromView = fromViewController.view;
        toView = toViewController.view;
    }
    
    BOOL isPresenting = (toViewController.presentingViewController == fromViewController);
    
    CGRect fromFrame = [transitionContext initialFrameForViewController:fromViewController];
    CGRect toFrame = [transitionContext finalFrameForViewController:toViewController];
    
    // Based on our configured targetEdge, derive a normalized vector that will
    // be used to offset the frame of the presented view controller.
    __block CGVector offset;
    if (self.targetEdge == UIRectEdgeTop)
        offset = CGVectorMake(0.f, 1.f);
    else if (self.targetEdge == UIRectEdgeBottom)
        offset = CGVectorMake(0.f, -1.f);
    else if (self.targetEdge == UIRectEdgeLeft)
        offset = CGVectorMake(1.f, 0.f);
    else if (self.targetEdge == UIRectEdgeRight)
        offset = CGVectorMake(-1.f, 0.f);
    else
        NSAssert(NO, @"targetEdge must be one of UIRectEdgeTop, UIRectEdgeBottom, UIRectEdgeLeft, or UIRectEdgeRight.");
    
    if (isPresenting)
    {
        // For a presentation, the toView starts off-screen and slides in.
        fromView.frame = fromFrame;
        toView.frame = CGRectOffset(toFrame, toFrame.size.width * offset.dx * -1,
                                    toFrame.size.height * offset.dy * -1);
    }
    else
    {
        fromView.frame = fromFrame;
        toView.frame = toFrame;
    }
    
    // We are responsible for adding the incoming view to the containerView
    // for the presentation.
    if (isPresenting)
    {
       [containerView addSubview:toView];
    }
    else
    {
        // -addSubview places its argument at the front of the subview stack.
        // For a dismissal animation we want the fromView to slide away,
        // revealing the toView.  Thus we must place toView under the fromView.
        [containerView insertSubview:toView belowSubview:fromView];
    }
    
    NSTimeInterval transitionDuration = [self transitionDuration:transitionContext];
    //動畫
    [UIView animateWithDuration:transitionDuration animations:^{
        if (isPresenting)
        {
            toView.frame = toFrame;
        }
        else
        {
            // For a dismissal, the fromView slides off the screen.
            fromView.frame = CGRectOffset(fromFrame, fromFrame.size.width * offset.dx,
                                          fromFrame.size.height * offset.dy);
        }
        
    } completion:^(BOOL finished) {
        BOOL wasCancelled = [transitionContext transitionWasCancelled];
        
        if (wasCancelled)
        {
           [toView removeFromSuperview];
        }
        
        [transitionContext completeTransition:!wasCancelled];
    }];;
}

使用的地方生成自定義轉場代理，將需要present的控制器的transitioningDelegate設置為此代理就可以看到presentViewController有了push的效果，dismiss有了pop的動畫效果。

轉場代理使用