解决显示多个gif图时，cpu使用过高导致手机温度上升或者内存占

显示gif图通常使用的方式如下：
1.使用UIImageView;
2,使用sdwebImage；
3,使用YYImage;
4,使用webview；

但是显示方式无非两种：
1：先一次性把gif图解析成多个图片，然后轮流播放这些图片,比如使用UIImageView和sdwebImage；这种方式因为要保存解析后的图片，所以占用内存比较高；
2，播放到哪一张图片时，去gif图中解析对应的这张照片，用完就释放，不占用内存，比如YYImage和webview，但是因为要频繁地解析图片，当照片分辨率很高时，会造成cpu占用率高，导致手机发热；

如果使用的gif图分辨率较低，影响还不是很大，个人测试当使用的gif图分辨率为1280*720，gif图大于8M，数量超过6个时，使用sdwebImage会由于内存暴涨导致崩溃；而使用YYImage虽然不会导致内存暴涨，但是cpu占用率过高导致手机温度上升；

综合考虑：不能使用内存暴增导致程序崩溃的方式，只能使用YYImage或者webview去显示；既然是因为图片分辨率高导致手机温度升高，如果把图片分辨率降低，就可以解决问题了。具体操作如下：
1，从相册选择图片后，使用ALAssetsLibrary取到图片的原始数据：

//获取选择的图片
-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info {
    [picker dismissViewControllerAnimated:YES completion:nil];
    [MeetHUD showLoadingTo:self.view animated:YES];
    __weak typeof(self)weakSelf = self;
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSURL *imageURL = [info valueForKey:UIImagePickerControllerReferenceURL];
        NSString *assetString = [imageURL absoluteString];
        __strong typeof(weakSelf)strongSelf = weakSelf;
        ALAssetsLibrary *assetLibrary = [[ALAssetsLibrary alloc]init];
        [assetLibrary assetForURL:imageURL resultBlock:^(ALAsset *asset) {
            ALAssetRepresentation *re = nil;
            if([assetString hasSuffix:@"GIF"] || [assetString hasSuffix:@"gif"]){
                re = [asset representationForUTI:(__bridge NSString *)kUTTypeGIF];
            } else {
                re = [asset defaultRepresentation];
            }
            NSUInteger size = [re size];
             uint8_t *buffer = malloc(size);
             NSError *error;
             NSUInteger bytes = [re getBytes:buffer fromOffset:0 length:size error:&error];
             NSData *data = [NSData dataWithBytes:buffer length:bytes];//这个就是选取的图片的原二进制数据
             free(buffer);
           NSData*scaleData = [self DataToScaleGifData: data];
         } failureBlock:^(NSError *error) {

         }];
    });
}

2，解析出gif图中的每张图片；

-(NSData*)DataToScaleGifData:(NSData*)data{
    CGImageSourceRef gifSource = CGImageSourceCreateWithData((__bridge CFDataRef)data, NULL);
    size_t gifCount = CGImageSourceGetCount(gifSource);
    NSMutableArray *scaleImgArray = [NSMutableArray array];
    NSTimeInterval totalDuration = 0;//播放的总时长
    float scale = 1;
    float imgSize = data.length/1024/1024;
//小于2M不进行缩放，2M带4M缩放60%，4M到8M缩放40%，超过8M缩放20%
    if(imgSize <= 2){
        scale = 1;
    } else if (imgSize > 2 && imgSize < 4){
        scale = 0.6;
    } else if(imgSize >= 4 && imgSize < 8){
        scale = 0.4;
    } else {
        scale = 0.2;
    }
  float imgWidth = 0;
  float imgHeight = 0;
    for (size_t i = 0; i< gifCount; i++) {
        CGImageRef imageRef = CGImageSourceCreateImageAtIndex(gifSource, i, NULL);
        imgWidth = CGImageGetWidth(imageRef);
        imgHeight = CGImageGetHeight(imageRef);
        UIImage *uiImage = [UIImage imageWithCGImage:imageRef];
        if(scale == 1){
            [scaleImgArray addObject:uiImage];
        } else {
            UIImage *scaleImg = [[self class] imageCompresswithsimple:uiImage scaledtosize:CGSizeMake(imgWidth*scale, imgHeight*scale)];
            [scaleImgArray addObject:scaleImg];
        }
        NSTimeInterval duration = [MeetVirtualHeaderTool gifImageDeleyTime:gifSource index:i];
        totalDuration += duration;
        CGImageRelease(imageRef);
    }
    CFRelease(gifSource);
  //重新生成一个缩放后的gif图data
    NSData *resultData = [[self class] creategifWithImgArray:scaleImgArray duration:totalDuration];
    return resultData;
}

图片缩放方法如下：

+ (UIImage*)imageCompresswithsimple:(UIImage*)image scaledtosize:(CGSize)size{
  UIGraphicsBeginImageContext(size);
  [image drawInRect:CGRectMake(0,0,size.width,size.height)];
    UIImage* newimage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return newimage;
}

重新生成缩放后的gif图data方法：

+ (NSData *)creategifWithImgArray:(NSArray *)imgArray duration:(float)duration{
    // 1.获取图片数据
    NSMutableArray *imageArray = [NSMutableArray arrayWithArray:imgArray];
    //每帧时长
    float perDuration = duration*1.0/imgArray.count;
    // 2.创建gif文件
    NSArray *document = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *docString = [document objectAtIndex:0];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSString *pathString = [docString stringByAppendingString:@"/gif"];
    [fileManager createDirectoryAtPath:pathString withIntermediateDirectories:YES attributes:nil error:nil];
    NSString *path = [pathString stringByAppendingString:@"test1.gif"];
    
    // 3.配置gif属性
    CGImageDestinationRef destion;
    // 将 path 映射成 CFURLRef 的路径
    CFURLRef url = CFURLCreateWithFileSystemPath(kCFAllocatorDefault, (CFStringRef)path, kCFURLPOSIXPathStyle, false);
    destion = CGImageDestinationCreateWithURL(url, kUTTypeGIF, imageArray.count, NULL);
    
//    [mutDict setObject:[NSNumber numberWithFloat:perDuration] forKey:kCGImagePropertyGIFUnclampedDelayTime];
    NSDictionary *dict = [NSDictionary dictionaryWithObject:[NSMutableDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:perDuration],(NSString *)kCGImagePropertyGIFDelayTime, nil] forKey:(NSString *)kCGImagePropertyGIFDelayTime];
    
    NSMutableDictionary *mutDict = [NSMutableDictionary dictionaryWithCapacity:2];
    [mutDict setObject:[NSNumber numberWithBool:YES] forKey:(NSString *)kCGImagePropertyGIFHasGlobalColorMap];
    [mutDict setObject:(NSString *)kCGImagePropertyColorModelRGB forKey:(NSString *)kCGImagePropertyColorModel];
    [mutDict setObject:[NSNumber numberWithInt:8] forKey:(NSString *)kCGImagePropertyDepth];
    [mutDict setObject:[NSNumber numberWithInt:0] forKey:(NSString *)kCGImagePropertyGIFLoopCount];
    NSDictionary *gifPropertyDict = [NSDictionary dictionaryWithObject:mutDict forKey:(NSString *)kCGImagePropertyGIFDictionary];
    
    CGImageDestinationSetProperties(destion, (__bridge CFDictionaryRef)gifPropertyDict);
    // 单帧添加到gif
    for (UIImage *image in imageArray) {
        CGImageDestinationAddImage(destion, image.CGImage, (__bridge CFDictionaryRef)dict);
    }
    CGImageDestinationFinalize(destion);
    CFRelease(destion);
    NSData *gifData = [NSData dataWithContentsOfFile:path];
    NSError *err;
    [fileManager removeItemAtPath:path error:&err];
    if(err == nil){
        
    }
    return gifData;
}

3,使用缩放后的data，不管是使用yyImage还是webView，cpu的使用率都降低了，手机也不再发热了，能够解决问题。
4，如果需要把原始数据传给服务器，可以再发送数据时，对缩小后的data进行放大处理，然后再发送给服务器，但是这种方式会造成gif图显示模糊，可以保留原始数据进行发送，也可以发送压缩后的数据。