执行多个连续 UIView 动画的最佳方法？

Question

我有一系列 8 个 UIView 动画，这些动画在我的视图加载后立即发生。现在，我通过使用animationDidStop:finished:context 委托方法来完成此任务，一切都按预期进行。问题是我对每个动画都有一个新方法。这些方法中的大部分代码都是重复的，只有动画持续时间和元素的实际位置发生变化。

我尝试创建一个将被调用的方法，并让上下文保存适当更改 UI 所需的参数，但它似乎递归地调用自身，远远超过了我调用它的次数：

-(void)animationDidStop:(NSString *)animationID finished:(BOOL)finished context:(void *)context{
    NSNumber *number = (NSNumber *)context;
    int animationStep = [number intValue];
    int nextAnimationStep = animationStep + 1;
    NSNumber *nextAnimationStepNumber = [NSNumber numberWithInt:nextAnimationStep];
    NSLog(@"Animation Step: %i", animationStep);

    CGRect firstFrame = CGRectMake(self.feedsScroll.frame.size.width * 2, 0.0f, self.secondFeedView.view.frame.size.width, self.secondFeedView.view.frame.size.height);
    CGRect thirdFrame = CGRectMake(self.feedsScroll.frame.size.width * 2, 0.0f, self.thirdFeedView.view.frame.size.width, self.thirdFeedView.view.frame.size.height);

    [UIView beginAnimations:nil context:nextAnimationStepNumber];
    [UIView setAnimationBeginsFromCurrentState:YES];
    [UIView setAnimationCurve:UIViewAnimationCurveLinear];
    [UIView setAnimationDelegate:self];

    if (animationStep < 8) 
        [UIView setAnimationDidStopSelector:@selector(animationDidStop:finished:context:)];

    NSLog(@"Beginning animations");

    switch (animationStep) {
        case 0:
            [UIView setAnimationDuration:.3];
            self.firstFeedView.view.center = CGPointMake(self.firstFeedView.view.center.x + 30, self.firstFeedView.view.center.y);
            break;
        case 1:
            [UIView setAnimationDuration:.3];
            self.firstFeedView.view.center = CGPointMake(self.firstFeedView.view.center.x  - 30, self.firstFeedView.view.center.y);
            break;
        case 2:
            [UIView setAnimationDuration:.3];
            [self.secondFeedView.view setFrame:firstFrame];
            break;
        case 3:
            [UIView setAnimationDuration:.3];
            self.secondFeedView.view.center = CGPointMake(self.secondFeedView.view.center.x + 30, self.firstFeedView.view.center.y);
            break;
        case 4:
            [UIView setAnimationDuration:.3];
            self.secondFeedView.view.center = CGPointMake(self.secondFeedView.view.center.x - 30, self.firstFeedView.view.center.y);
            break;
        case 5:
            NSLog(@"Animation step 6");
            [UIView setAnimationDuration:.5];
            self.firstFeedView.view.center = CGPointMake(self.firstFeedView.view.center.x - 230, self.firstFeedView.view.center.y);
            self.secondFeedView.view.center = CGPointMake(self.secondFeedView.view.center.x - 230, self.firstFeedView.view.center.y);
            break;
        case 6:
            [UIView setAnimationDuration:.5];
            [self.thirdFeedView.view setFrame:thirdFrame];
            break;
        case 7:
            [UIView setAnimationDuration:.3];
            self.thirdFeedView.view.center = CGPointMake(self.thirdFeedView.view.center.x + 30, self.firstFeedView.view.center.y);
            break;
        case 8:
            [UIView setAnimationDuration:.3];
            self.thirdFeedView.view.center = CGPointMake(self.thirdFeedView.view.center.x - 30, self.thirdFeedView.view.center.y);
            break;
        default:
            break;
    }

    [UIView commitAnimations];  
}

我知道这可能是一个天真的想法执行。我是 iPhone 开发新手，正在寻找一些可以在这里应用的最佳实践。我是否以错误的方式处理这件事？

Answer 1

如果您愿意升级到 iOS 4.0，新的基于块的动画方法可以使动画链接变得微不足道。例如：

[UIView animateWithDuration:1.0 animations:^{ view.position = CGPointMake(0.0f, 0.0f); } completion:^(BOOL finished){
    [UIView animateWithDuration:0.2 animations:^{ view.alpha = 0.0; } completion:^(BOOL finished){
        [view removeFromSuperview]; }];
}]

将导致 view 在 1 秒的时间内动画到 (0, 0)，淡出 0.2 秒，然后从其超级视图中删除。这些动画将是连续的。

+animateWithDuration:animations:completion: 类方法中的第一个块包含立即进行动画处理的属性更改，第二个块是动画完成时要执行的操作。由于此回调可以包含此类的另一个动画，因此您可以嵌套它们以创建任意动画链。

Answer 2

您可以使用块来实现此目的并获得非常干净的结果。

NSMutableArray* animationBlocks = [NSMutableArray new];

typedef void(^animationBlock)(BOOL);

// getNextAnimation
// removes the first block in the queue and returns it
animationBlock (^getNextAnimation)() = ^{
    animationBlock block = (animationBlock)[animationBlocks firstObject];
    if (block){
        [animationBlocks removeObjectAtIndex:0];
        return block;
    }else{
         return ^(BOOL finished){};
    }
};

//add a block to our queue
[animationBlocks addObject:^(BOOL finished){;
    [UIView animateWithDuration:1.0 animations:^{
        //...animation code...
    } completion: getNextAnimation()];
}];

//add a block to our queue
[animationBlocks addObject:^(BOOL finished){;
    [UIView animateWithDuration:1.0 animations:^{
        //...animation code...
    } completion: getNextAnimation()];
}];

//add a block to our queue
[animationBlocks addObject:^(BOOL finished){;
    NSLog(@"Multi-step Animation Complete!");
}];

// execute the first block in the queue
getNextAnimation()(YES);

摘自：http://xibxor.com/objective-c/uiview-animation-without-嵌套地狱/

Answer 3

我们创建了一个组件，用于使用块以声明方式链接动画步骤（Github 上的 CPAnimationSequence）。我们在我们的 iOS 开发博客中描述了动机和基本原理。

它为您提供了非常可读的代码，如下所示：

[[CPAnimationSequence sequenceWithSteps:
    [CPAnimationStep           for:0.25 animate:^{ self.imageView.alpha = 0.0; }],
    [CPAnimationStep           for:0.25 animate:^{ self.headline.alpha = 0.0;  }],
    [CPAnimationStep           for:0.25 animate:^{ self.content.alpha = 0.0;   }],
    [CPAnimationStep after:1.0 for:0.25 animate:^{ self.headline.alpha = 1.0;  }],
    [CPAnimationStep           for:0.25 animate:^{ self.content.alpha = 1.0;   }],
    nil]
runAnimated:YES];

Answer 4

“上下文”是 void*，因此不保留。有几个选项：

• 设置时保留它。在回调开始时自动释放它。这感觉很恶心（Objective-C 函数应该适当地保留/释放，但不幸的是上下文不是id）。
• 将数字存储在字符串中：intanimationStep = [animationID intValue];和[UIView beginAnimations:[NSString stringWithFormat:@"%d", nextAnimationStep] context:NULL];。这也让人感觉恶心。
• 假设 UIKit/CoreAnimation 不取消引用指针，int AnimationStep = (int)context; 和 [UIView beginAnimations:nil context:(void*)nextAnimationStep];。这很糟糕（根据 C 标准，可能会导致未定义的行为）。

另一方面，finished:(BOOL)finished 应该是 finished:(NSNumber*)finished。他们在原始文档中犯了一个错误；更改文档以反映 API 可能更容易，而不是更改 API 并必须神奇地保持向后兼容性（即使传递 bool 更明智）。

Answer 5

 // create the view that will execute our animation
 UIImageView* logo = [[UIImageView alloc] initWithFrame:self.view.frame];
 // load all the frames of our animation
 logo.animationImages = [NSArray arrayWithObjects:  
                                 [UIImage imageNamed:@"frame_00001.png"],

                         [UIImage imageNamed:@"frame_00002.png"],
                         [UIImage imageNamed:@"frame_00003.png"],
                         [UIImage imageNamed:@"frame_00004.png"],
                                 [UIImage imageNamed:@"frame_00005"], nil];

 // all frames will execute in 3 seconds
 logo.animationDuration =3.3;
 // repeat the annimation forever
logo.animationRepeatCount = 1;
 // start animating
 [logo startAnimating];
 // add the animation view to the main window 
 [self.view addSubview:logo];
 [logo release]; 

将其放入 ViewDidLoad 中