使用kCAMediaTimingFunctionEaseIn是否有问题？

我正在使用CALayer，CAReplicatorLayer并CABasicAnimation设置条形图的动画。条形图由“段”组成，我将其渲染为带有的小矩形CALayer。然后，将它们作为子层添加到CAReplicatorLayer循环中。最后，我为每个小矩形添加一个动画，将该矩形放到图表中的位置。

这是动画的最终状态：

这是动画中间的样子：

这是实现它的代码：

#define BLOCK_HEIGHT 6.0f
#define BLOCK_WIDTH 8.0f

@interface TCViewController ()

@property (nonatomic, strong) NSMutableArray * blockLayers;         // blocks that fall from the sky
@property (nonatomic, strong) NSMutableArray * replicatorLayers;    // replicator layers that will replicate the blocks into position

@end

@implementation TCViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor lightGrayColor];

    self.blockLayers = [NSMutableArray array];
    self.replicatorLayers = [NSMutableArray array];

    NSArray * dataBlocksData = @[@1,@2,@3,@1,@5,@2,@11,@14,@5,@12,@10,@3,@7,@6,@3,@4,@1];

    __block CGFloat currentXPosition = 0.0f;

    [dataBlocksData enumerateObjectsUsingBlock:^(NSNumber * obj, NSUInteger idx, BOOL *stop) {

        currentXPosition += BLOCK_WIDTH + 2.0f;

        if (obj.integerValue == 0) return;

        // replicator layer for data blocks in a column
        CAReplicatorLayer * replicatorLayer = [[CAReplicatorLayer alloc] init];
        replicatorLayer.frame = CGRectMake(currentXPosition, 0.0f, BLOCK_WIDTH, 200.0f);

        // single data block layer (must be new for each replicator layer. can't reuse existing layer)
        CALayer * blockLayer = [[CALayer alloc] init];
        blockLayer.frame = CGRectMake(0, 200-BLOCK_HEIGHT, BLOCK_WIDTH, BLOCK_HEIGHT);
        blockLayer.backgroundColor = [UIColor whiteColor].CGColor;
        [replicatorLayer addSublayer:blockLayer];

        replicatorLayer.instanceCount = obj.integerValue;
        replicatorLayer.instanceDelay = 0.1f;
        replicatorLayer.instanceTransform = CATransform3DMakeTranslation(0, -BLOCK_HEIGHT, 0);    // negative height moves back up the column

        [self.blockLayers addObject:blockLayer];                
        [self.replicatorLayers addObject:replicatorLayer];      
    }];
}

- (void)viewDidLayoutSubviews {
    // add replicator layers as sublayers
    [self.replicatorLayers enumerateObjectsUsingBlock:^(CAReplicatorLayer * obj, NSUInteger idx, BOOL *stop) {
        [self.view.layer addSublayer:obj];
    }];
}

- (void)viewDidAppear:(BOOL)animated {

    // add animations to each block layer
    [self.blockLayers enumerateObjectsUsingBlock:^(CALayer * obj, NSUInteger idx, BOOL *stop) {
        // position animation
        CABasicAnimation * animation = [CABasicAnimation animationWithKeyPath:@"transform.translation.y"];
        animation.fromValue = @(-300);
        animation.toValue = @(0);
        animation.duration = 1.0f;
        animation.fillMode = kCAFillModeBoth;
        animation.removedOnCompletion = NO;
        animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionDefault];
        [obj addAnimation:animation forKey:@"falling-block-animation"];
    }];
}

最后，这是要抓住的地方。如果指定no timingFunction，则一个Linear或EaseIn多个动画不会完全完成。就像块没有完全落入位。看来他们快要完成了，但还差得很远。只需关闭一两帧即可。交换定时功能分配-viewDidAppear:，您将得到以下怪异：

继续尝试一下。我什至尝试通过控制点（link）指定一个功能，该功能与功能完全相同EaseIn：

// use control points for an EaseIn timing:
animation.timingFunction = [CAMediaTimingFunction functionWithControlPoints:0.42 :0.00 :1.0 :1.0];

// or simply specify the ease in timing function:
animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];

出于某种原因EaseOut，Default定时功能可以正常工作，但样式上的简便似乎需要更长的时间才能完成（在视觉上），这也许是因为插值曲线的长度吗？

我已经尝试了许多方法来缩小问题的范围：

1. Not looping over these structures and using only 1 layer and 1 replicator layer with the same animation. By that I mean, animate just one column. No luck. Looping isn't the issue.
2. Put the creation, sublayer-adding and animation-adding code all in -viewDidAppear. Didn't seem to make a difference if the animations were added earlier or later in the view's life cycle.
3. Using properties for my structures. No difference.
4. Not using properties for my structures. Again, no difference.
5. Added callbacks for animation completion to remove the animation so as to leave the columns in the correct "final" state. This was not good but worth a try.
6. The issue is present in both iOS 6 and 7.

I really want to use an EaseIn timing function because its the best looking animation for something falling into place. I also want to use the CAReplicatorLayer because it does exactly what I want to do.

So what's wrong with the EaseIn timing functions as I'm using them? Is this a bug?