ios - 使用自定义 segue 转到 ViewController 会导致 viewWillAppear 被调用两次

Question

我写了一个自定义转场，因为我想给它添加我自己的动画。除了目标 View CiewController 中的 viewDidLoad 方法被调用两次之外，一切正常。这是我的 segue 的执行方法:

- (void)perform
{
    UIViewController* sourceViewController = self.sourceViewController;
    UIViewController* destinationViewController = self.destinationViewController;

    [sourceViewController.view addSubview:destinationViewController.view];

    CGPoint originalCenter = destinationViewController.view.center;
    destinationViewController.view.center = CGPointMake(self.originatingPoint.x * 3, self.originatingPoint.y);

    [UIView animateWithDuration:0.25
        delay:0.0
        options:UIViewAnimationOptionCurveEaseInOut
        animations:^{
            destinationViewController.view.center = originalCenter;
        }
        completion:^(BOOL finished) {
            [sourceViewController presentViewController:destinationViewController animated:NO completion:NULL]; // present VC
        }];
}

有人知道是什么原因造成的吗？

[----- 编辑 -----]

segue 作为自定义 segue 出现在故事​​板中，带有我自己编写的 segue 类。在我的类(class)中唯一不同的是我在上面提出的执行方法。通过按钮调用segue，只调用一次prepareForSegue方法。

[----- 编辑 2 -----]

我检查了 targetVC 的 viewDidLoad 方法，每个 segue 只调用一次。尽管如此，使用 viewWillAppear 对我来说会方便得多，所以您是否知道我制作此动画的不同方式？

Answer 1

我建议您使用 UIViewControllerTransitioningDelegate 和 UIViewControllerAnimatedTransitioning，它们是自 iOS 7.0 以来更适合用于转换的约定。从 iOS 8.0 开始，您还获得了 UIPresentationController 支持，这使您可以构建更丰富的过渡效果。

例子:

@interface ModalTransitionAnimator : NSObject<UIViewControllerAnimatedTransitioning>

@property (nonatomic) CGPoint originatingPoint;

@end

@implementation ModalTransitionAnimator

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext {
    return 0.25;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
    NSTimeInterval duration = [self transitionDuration:transitionContext];
    UIView* sourceView = [transitionContext viewForKey:UITransitionContextFromViewKey];
    UIView* destinationView = [transitionContext viewForKey:UITransitionContextToViewKey];
    UIView* container = transitionContext.containerView;

    [container addSubview:destinationView];

    CGPoint originalCenter = destinationView.center;

    destinationView.center = CGPointMake(self.originatingPoint.x * 3, self.originatingPoint.y);

    [UIView animateWithDuration:duration animations:^{
            destinationView.center = originalCenter;
        }
        completion:^(BOOL finished) {
            [transitionContext completeTransition:YES];
        }];
}

@end

然后在 prepareForSegue 中，您只需分配转换委托(delegate)并实现 UIViewControllerTransitioningDelegate 以返回适当的动画师以进行演示或解雇。

@interface ViewController : UIViewController<UIViewControllerTransitioningDelegate>
@end

@implementation ViewController

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    UIViewController* controller = (UIViewController*)segue.destinationViewController;

    controller.transitioningDelegate = self;
    controller.modalPresentationStyle = UIModalPresentationCustom;
    controller.modalPresentationCapturesStatusBarAppearance = YES;
}

- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source {
    ModalTransitionAnimator *animator = [[ModalTransitionAnimator alloc] init];
    animator.originatingPoint = /* ... */;

    return animator;
}

@end

因为这是一个模态转换，你必须使用 presentViewController:animated: 来呈现 Controller 。因此，在 Storyboards 中使用正常的“显示”segues，它们将自动运行引擎盖下的所有动画，无需在这里重新发明 segues。

我在 Github 的某处有关于如何构建自定义转换的示例:

https://github.com/pronebird/CustomModalTransition/tree/ios8