iOS 自定义高性能加载gif

一·实现的各种方式

1.将GIF图片分解成多张PNG图片，使用UIImageView播放(内存消耗过大）
2.使用YYImage中的YYAnimatedImageView播放，推荐，内存优化的挺好，是个高性能的框架。

这里就不详细说明YYAnimatedImageView的实现方式了。其核心思想就是 解压gif成图片数组，利用CADisplaylink进行按帧动画显示

二·自己实现播放gif，学习内部细节

1.属性

/// 用于展示帧动画
@property (nonatomic, strong) CADisplayLink *displayLink;
/// 图片数组
@property (nonatomic, strong) NSArray *imageArray;
/// 当前帧
@property (nonatomic, assign) NSInteger currentIndex;
/// 是否正在显示
@property (nonatomic, assign, getter=isAnimation) BOOL animation;
/// 总的时间
@property (nonatomic, assign) NSTimeInterval timeDuration;
/// 是否重复
@property (nonatomic, assign, getter=isRepeat) BOOL repeat;

2.解压gif

/// 获取资源
- (void)loadGif:(NSString *)gif isRepeat:(BOOL)repeat {

    self.repeat = repeat;
    
    //1.加载Gif图片，转换成Data类型
    NSString *path = [NSBundle.mainBundle pathForResource:gif ofType:@"gif"];
    NSData *data = [NSData dataWithContentsOfFile:path];
    
    //2.将data数据转换成CGImageSource对象
    CGImageSourceRef imageSource = CGImageSourceCreateWithData(CFBridgingRetain(data), nil);
    size_t imageCount = CGImageSourceGetCount(imageSource);
    //3.遍历所有图片
    NSMutableArray *images = [NSMutableArray array];
    NSTimeInterval totalDuration = 0;
    for (int i = 0; i<imageCount; i++) {
        //取出每一张图片
        CGImageRef cgImage = CGImageSourceCreateImageAtIndex(imageSource, i, nil);
        UIImage *image = [UIImage imageWithCGImage:cgImage];
        [images addObject:image];
        
        //持续时间
        NSDictionary *properties = (__bridge_transfer  NSDictionary*)CGImageSourceCopyPropertiesAtIndex(imageSource, i, nil);
        NSDictionary *gifDict = [properties objectForKey:(__bridge NSString *)kCGImagePropertyGIFDictionary];
        NSNumber *frameDuration =
        [gifDict objectForKey:(__bridge NSString *)kCGImagePropertyGIFDelayTime];
        totalDuration += frameDuration.doubleValue;
    }
    
    self.imageArray = [images copy];
    self.timeDuration = totalDuration;
    self.currentIndex = 0;
}

3.利用CADisplaylink实现播放

- (void)display {
    
    if ([self.imageArray isEqual:nil] || self.imageArray.count == 0) {
        [self stopAnimating];
        return;
    }
    if (self.currentIndex > self.imageArray.count) {
        if (self.repeat) {
            self.currentIndex = 0;
            [self startAnimating];
            return;
        } else {
            [self stopAnimating];
            return;
        }
    }
}

- (CADisplayLink *)displayLink {
    if (!_displayLink) {
        _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(display)];
        // 当把 CADisplayLink 对象添加到 Runloop 中后，selector就能被周期性调用
        [self.displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
    }
    return _displayLink;
}