在iOS10上生成的GIF图像不再在浏览器上永久循环

Question

这是一个生成GIF图像的ObjectiveC方法：

@implementation NSArray (GIFImage)

- (NSString*)GIFImageWithImageDuration:(CGFloat)GIFImageDuration
{
    NSArray *images = self;

    NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"animated.gif"];
    CGImageDestinationRef destination = CGImageDestinationCreateWithURL((CFURLRef)[NSURL fileURLWithPath:path],
                                                                        kUTTypeGIF,
                                                                        images.count,
                                                                        NULL);

    NSDictionary *frameProperties = [NSDictionary dictionaryWithObject:[NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:GIFImageDuration]
                                                                                                   forKey:(NSString *)kCGImagePropertyGIFDelayTime]
                                                                forKey:(NSString *)kCGImagePropertyGIFDictionary];


    NSDictionary *gifProperties = [NSDictionary dictionaryWithObject:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:0] forKey:(NSString *)kCGImagePropertyGIFLoopCount]
                                                              forKey:(NSString *)kCGImagePropertyGIFDictionary];

    for ( NSInteger index = 0; index < images.count; index++ )
    {
        UIImage *image = (UIImage *)[images objectAtIndex:index];
        CGImageDestinationAddImage(destination, image.CGImage, (CFDictionaryRef)frameProperties);
    }

    CGImageDestinationSetProperties(destination, (CFDictionaryRef)gifProperties);
    CGImageDestinationFinalize(destination);
    CFRelease(destination);
    NSLog(@"animated GIF file created at %@", path);
    return path;
}

@end

在iOS9上运行此方法效果很好，GIF在浏览器上永久生成循环：

在iOS10上运行相同的方法失败，GIF在浏览器上不再生成永久循环，它只播放一次：

此外，受到这个答案的启发：https://stackoverflow.com/a/38082881/448662，我对iOS9和iOS10中生成的两个GIF进行了十六进制比较，看来iOS10生成的GIF中缺少一个段（Netscape应用程序扩展），这可能是它不循环的原因，但我不能确定。

简而言之，我们如何生成在浏览器上永久循环的GIF图像（使用ObjectiveC）？

Answer 1

我在最近的GitHub回购提交中找到了解决方案： https://github.com/NSRare/NSGIF/pull/23/files?diff=split

基本上，在 CGImageDestinationAddImage 之前调用 CGImageDestinationSetProperties 解决了iOS10上的问题。

这是工作代码：

@implementation NSArray (GIFImage)
- (NSString*)GIFImageWithImageDuration:(CGFloat)GIFImageDuration
{
    NSArray *images = self;

    NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"animated.gif"];
    CGImageDestinationRef destination = CGImageDestinationCreateWithURL((CFURLRef)[NSURL fileURLWithPath:path],
                                                                        kUTTypeGIF,
                                                                        images.count,
                                                                        NULL);

    NSDictionary *frameProperties = [NSDictionary dictionaryWithObject:[NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:GIFImageDuration]
                                                                                                   forKey:(NSString *)kCGImagePropertyGIFDelayTime]
                                                                forKey:(NSString *)kCGImagePropertyGIFDictionary];


    NSDictionary *gifProperties = [NSDictionary dictionaryWithObject:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:0] forKey:(NSString *)kCGImagePropertyGIFLoopCount]
                                                              forKey:(NSString *)kCGImagePropertyGIFDictionary];

    CGImageDestinationSetProperties(destination, (CFDictionaryRef)gifProperties);

    for ( NSInteger index = 0; index < images.count; index++ )
    {
        UIImage *image = (UIImage *)[images objectAtIndex:index];
        CGImageDestinationAddImage(destination, image.CGImage, (CFDictionaryRef)frameProperties);
    }

    CGImageDestinationFinalize(destination);
    CFRelease(destination);
    NSLog(@"animated GIF file created at %@", path);
    return path;
}