核心动画“翻转”动画

我希望使用 Core Animation 在 Mac 应用程序中模拟翻转时钟动画。目前我有三个 CALayer 代表数字的上半部分和下半部分，第三个用于代表翻转动画（在以下文章中找到了解决方案：使用 Core Animation 创建 iPad 翻转时钟 http://www.voyce.com/index.php/2010/04/10/creating-an-ipad-flip-clock-with-core-animation/.

翻转层的动画分为两个阶段：从数字顶部翻转到数字中间，然后从中间翻转到底部。为了实现这一点，我使用了一个委托函数，每当动画结束时就会调用该函数：

- (void)animationDidStop:(CAAnimation *)oldAnimation finished:(BOOL)flag
{
    int digitIndex = [[oldAnimation valueForKey:@"digit"] intValue];    
    int currentValue = [[oldAnimation valueForKey:@"value"] intValue];

    NSMutableArray *digit = [digits objectAtIndex:digitIndex];
    CALayer *flipLayer = [digit objectAtIndex:tickerFlip];
    CALayer *bottomLayer = [digit objectAtIndex:tickerBottom];

    if([[oldAnimation valueForKey:@"state"] isEqual:@"top"] && flag) {
        NSLog(@"Top animation finished");

        [CATransaction begin];
        [CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions];
        flipLayer.contents = [bottomImages objectAtIndex:currentValue];
        flipLayer.anchorPoint = CGPointMake(0.0, 1.0);
        flipLayer.hidden = NO;
        [CATransaction commit];

        CABasicAnimation *anim = [self generateAnimationForState:@"bottom"];
        [anim setValue:[NSString stringWithFormat:@"%d", digitIndex] forKey:@"digit"];
        [anim setValue:[NSString stringWithFormat:@"%d", currentValue] forKey:@"value"];
        [flipLayer addAnimation:anim forKey:nil];
    } else if([[oldAnimation valueForKey:@"state"] isEqual:@"bottom"] && flag) {
        NSLog(@"Bottom animation finished");

        // Hide our flip layer
        [CATransaction begin];
        [CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions];
        bottomLayer.contents = [bottomImages objectAtIndex:currentValue];
        flipLayer.hidden = YES;
        flipLayer.anchorPoint = CGPointMake(0.0, 0.0);
        [CATransaction commit];
    }
}

此委托函数使用辅助函数，该函数根据翻转层的状态生成翻转层的变换：

- (CABasicAnimation *)generateAnimationForState:(NSString *)state
{
    CABasicAnimation *anim = [CABasicAnimation animationWithKeyPath:@"transform"];
    anim.duration = 0.15;
    anim.repeatCount = 1;

    // Check which animation we're doing
    if([state isEqualToString:@"top"]) 
    {
        anim.fromValue = [NSValue valueWithCATransform3D:CATransform3DMakeRotation(0.0f, 1, 0, 0)];
        anim.toValue = [NSValue valueWithCATransform3D:CATransform3DMakeRotation(M_PI/2, 1, 0, 0)];
    } 
    else 
    {
        anim.fromValue = [NSValue valueWithCATransform3D:CATransform3DMakeRotation(-M_PI/2, 1, 0, 0)];
        anim.toValue = [NSValue valueWithCATransform3D:CATransform3DMakeRotation(0.0f, 1, 0, 0)];
    }

    anim.delegate = self;
    anim.removedOnCompletion = NO;

    // Set our animations state
    [anim setValue:state forKey:@"state"];

    return anim;
}

此解决方案有效，但在动画进行时会导致一些轻微的闪烁。我相信这是由于我的翻转层在“顶部”和“底部”动画之间重置的转换造成的。需要注意的是，在动画的第一阶段完成后，我将翻转图层锚点设置到图像的顶部，以确保翻转枢轴正确。

目前我不确定我的动画是否已设置最佳。总的来说，我对转换和核心动画很陌生。有人能指出我正确的方向吗？

After

anim.removedOnCompletion = NO; 

尝试插入此代码：

anim.fillMode = kCAFillModeForwards;

让我知道。本质上，代码片段应该防止导致闪烁的“重置”。