在Twitter上分享时，GIF不会制作动画 [英] GIF do not animate when share on twitter

问题描述

我正在使用 NSArray 创建 UIImage 的动画GIF文件。并将其保存在 NSDocumentDirectory 以及iPhone的相册中。

I am creating animated GIF file with NSArray of UIImage. And saving it in NSDocumentDirectory as well as in Photo Album of iPhone.

我面临的问题是，当我在Email Composer或iMessage中打开保存的GIF，它动画很好。但是，当我通过推特分享它时，它没有动画。我尝试通过iPhone上的Twitter应用程序分享并看到一个有趣的事情（下面的ScreenShot）我使用Safari从不同网站下载的GIF在GIF的左上角显示标签'GIF'。虽然我保存的GIF没有。这可能是什么问题？任何人都可以指导我。

The problem I am facing is, when I open the saved GIF in Email Composer or in iMessage, it animates fine. But when i share it through twitter, it does not animate. I tried sharing through twitter app on iPhone and saw an Interesting thing(ScreenShot below) that The GIFs i downloaded from different websites using Safari shows a label 'GIF' on top left corner of GIF. While my saved GIFs does not. What might be the problem here? Can anyone please guide me.

以下是创建GIF文件的代码：

Here is the code for creating the GIF file:

float delay = 1.0/15.0; // 15 FPS

NSDictionary *prep = @{
                       (__bridge id)kCGImagePropertyGIFDictionary: @{
                               (__bridge id)kCGImagePropertyGIFDelayTime: @(delay) 
                               }
                       };

//    static NSUInteger kFrameCount = 16;

NSDictionary *fileProperties = @{
                                 (__bridge id)kCGImagePropertyGIFDictionary: @{
                                         (__bridge id)kCGImagePropertyGIFLoopCount: @0 // 0 means loop forever
                                         }
                                 };

CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:path];

CGImageDestinationRef dst = CGImageDestinationCreateWithURL(url, kUTTypeGIF, [images count], nil);
CGImageDestinationSetProperties(dst, (__bridge CFDictionaryRef)fileProperties);

for (int i=0;i<[images count];i++)
{
        //load anImage from array
        UIImage * anImage = [images objectAtIndex:i];

        CGImageDestinationAddImage(dst, anImage.CGImage,(__bridge CFDictionaryRef)prep);

}

bool fileSave = CGImageDestinationFinalize(dst);
CFRelease(dst);
if(fileSave) {
    NSLog(@"animated GIF file created at %@", path);
}else{
    NSLog(@"error: no animated GIF file created at %@", path);
}

并将GIF保存到相册和NSDocumentDirectory中。要保存在iPhone的相册中，请输入以下代码：

And saving the GIF into Photo Album as well as in NSDocumentDirectory. To save in Photo Album of iPhone, here is the code:

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];

NSData *data = [NSData dataWithContentsOfFile:tempPath];

[library writeImageDataToSavedPhotosAlbum:data metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {
    if (error) {
        NSLog(@"Error Saving GIF to Photo Album: %@", error);
    } else {
        // TODO: success handling
        NSLog(@"GIF Saved to %@", assetURL);

        success(tempPath);
    }
}];

HJImagesToGIF 是一个很大的帮助，以及这个要点！

HJImagesToGIF was big help, as well as this gist!

更新：

在分析2个GIF的图像标题时：
1-图像标题： GIF89a - 通过safari下载并在Twitter应用中显示GIF标签
2-图像标题： GIF87a - 通过代码创建，不显示GIF标签在Twitter应用程序

On analysing the Image Header of 2 GIFs: 1- Image Header: GIF89a - downloaded through safari and shows GIF label in twitter app 2- Image Header: GIF87a - Created through code, doesnt show GIF label in twitter app

所以图像标题！嗯..我该怎么改呢？

So the Image Header! hmmm.. how do I change it?

推荐答案

好的，所以解决了这个问题，我不确定它是不是最好的解决方案，并希望得到更好的解决方案！

Ok so solved the issue, I am not sure if its the best solution, and would appreciate better solutions from anyone!

这个问题确实与我通过Code创建的GIF图像标题有关。
我拿了一个GIF89a标头GIF并复制了标题（前6个字节）并用它替换了我的GIF图像标题。现在在推特以及电子邮件和iMessage上正常工作。

The problem was indeed related to the image header of the GIFs which I created through Code. I took a GIF89a header GIF and copied the header (first 6 bytes) and replaced my GIF's image header with it. Working fine now on twitter as well as email and iMessage.

以下是我使用的代码：

NSMutableData *gifData = [NSMutableData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"1.gif" ofType:nil]]; // GIF89a file
NSMutableData *data = [NSMutableData dataWithContentsOfFile:path]; // My created GIF file 
NSMutableData *gif89 = [NSMutableData dataWithData:[gifData subdataWithRange:NSMakeRange(0, 6)]]; // the first 6 bytes we needed (or the Header)
[data replaceBytesInRange:NSMakeRange(0, 6) withBytes:gif89.bytes]; // replace the header.. Voila! 

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