動畫AVPlayerLayer videoGravity屬性

Question

我正在嘗試復制Apple在視頻播放中的行為，允許用戶拉伸視頻圖像以填充邊界。

@interface FHVideoPlayerView : UIView
@end
@interface FHVideoPlayerView

+ (Class)layerClass
{
    return [AVPlayerLayer class];
}

- (void)setAspectMode:(FHVideoPlayerAspectMode)aspectMode animated:(BOOL)animated
{
    FHVideoPlayerAspectMode current = [self aspectMode];
    FHVideoPlayerAspectMode final   = aspectMode;

    NSString *fromValue;
    NSString *toValue;

    AVPlayerLayer *layer = (AVPlayerLayer *)[self layer];

    switch (current) {
        case FHVideoPlayerAspectFill:
            fromValue = AVLayerVideoGravityResizeAspectFill;
            break;
        case FHVideoPlayerAspectFit:
            fromValue = AVLayerVideoGravityResizeAspect;
            break;
       default:
           break;
    }

    switch (final) {
        case FHVideoPlayerAspectFill:
            toValue = AVLayerVideoGravityResizeAspectFill;
            break;
        case FHVideoPlayerAspectFit:
            toValue = AVLayerVideoGravityResizeAspect;
            break;
        default:
            break;
    }

    if (toValue != fromValue) {
        if (animated == YES) {
            // Manually added CABasicAnimation based on the understanding the implicit animations are disabled for CALayers that back a UIView
            CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"videoGravity"];
            [layer addAnimation:animation forKey:@"animateVideoGravity"];

            [CATransaction begin];
            [CATransaction setAnimationDuration:0.333];
        }

        [layer setVideoGravity:toValue];

        if (animated == YES) {
            [CATransaction commit];
        }
    }
}

當我嘗試為不透明度這樣的數字屬性設置動畫時，這很好用。 但是，你會從類引用中注意到，AVPlayerLayer的videoGravity屬性是一個NSString。 類引用確實指出它是可動畫的。

所以我的問題是：如何！？

我相信這可能與CALayer的內容屬性以及可能的contentsGravity有某種關系。

Answer 1

正如voromax所指出的，這是iOS 5.0中的一個錯誤。 我在iOS 5.1中進行了逆向工程-[AVPlayerLayer setVideoGravity:]實現，以便了解動畫應該如何工作。 以下是如何解決這個錯誤，並在iOS 5.0上有一個很好的動畫。

@implementation VideoPlayerView

+ (Class) layerClass
{
    return [AVPlayerLayer class];
}

- (AVPlayerLayer *) playerLayer
{
    return (AVPlayerLayer *)[self layer];
}

- (NSString *) videoGravity
{
    return self.playerLayer.videoGravity;
}

- (void) setVideoGravity:(NSString *)videoGravity
{
    self.playerLayer.videoGravity = videoGravity;

    // Workaround a bug in iOS 5.0
    float avFoundationVersion = [[[NSBundle bundleForClass:[AVPlayerLayer class]] objectForInfoDictionaryKey:(NSString *)kCFBundleVersionKey] floatValue];
    if (avFoundationVersion < 292.24f)
    {
        @try
        {
            NSString *contentLayerKeyPath = [NSString stringWithFormat:@"%1$@%2$@.%3$@%2$@", @"player", [@"layer" capitalizedString], @"content"]; // playerLayer.contentLayer
            CALayer *contentLayer = [self.playerLayer valueForKeyPath:contentLayerKeyPath];
            if ([contentLayer isKindOfClass:[CALayer class]])
                [contentLayer addAnimation:[CABasicAnimation animation] forKey:@"sublayerTransform"];
        }
        @catch (NSException *exception)
        {
        }
        self.bounds = self.bounds;
    }
}

@end

Answer 2

這是iOS 5.0和iOS 5.0.1中的一個錯誤。

更新到iOS 5.1后，視頻重力變化動畫再次開始工作。