ios - 为什么我无法使用 [transitionContext viewControllerForKey :UITransitionContextFromViewKey] 获取 FromVC 和 ToVC

Question

我遇到了一个问题:

当我尝试覆盖方法 startInteractiveTransition: 时，我尝试保存 transitionContext，并获取 FromVC 和 ToVC来自 transitionContext但是失败了，不知为什么？有人有想法吗？

代码如下:

-(void)startInteractiveTransition:(id<UIViewControllerContextTransitioning>)transitionContext
{
    self.transitionContext = transitionContext;
    id<UIViewControllerContextTransitioning> transitionContext01 = self.transitionContext;
    if (self.transitionContext) {
        NSLog(@"start里为空");
    }else
    {
        NSLog(@"start里不为空");
    }
    NSLog(@"执行了start");
    UIViewController * fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewKey];
    if (fromVC) {
        NSLog(@"start里fromVC为空");
    }else
    {
        NSLog(@"start里fromVC不为空");
    }
    UIViewController * toVC = [transitionContext viewControllerForKey:UITransitionContextToViewKey];
    if (toVC) {
        NSLog(@"start里toVC为空");
    }else
    {
        NSLog(@"start里toVC不为空");
    }
    [[transitionContext containerView] bringSubviewToFront:fromVC.view];
    toVC.view.alpha = self.behindViewAlpha;
}

截图如下: screenshot

Answer 1

自己找issur不是UITransitionContextToViewKey但是UITransitionContextToViewControllerKey