iOS_UIImage显示GIF图

一、原理

gif的显示是图片的叠加，因此可以根据这个特征来实现我们的想法：

1. 使用ImageIO库中的CGImageSource获取数据源
2. CGImageSourceGetCount获取GIF图片的数量，并计算出每一张图显示的时间
3. 写入一个新的UIImage对象中，并返回给UIImageView

二、代码实现

代码来自SDWebImage

• UIImage+GIF.h

#import 

@interface UIImage (GIF)

//加载保存在本地的gif图片
+ (UIImage *)sd_animatedGIFNamed:(NSString *)name;

//获取到图片的data后重新构造一张可以播放的图片
+ (UIImage *)sd_animatedGIFWithData:(NSData *)data;

//图片按照指定的尺寸缩放
- (UIImage *)sd_animatedImageByScalingAndCroppingToSize:(CGSize)size;

@end

---

• UIImage+GIF.m

#import "UIImage+GIF.h"
#import 

@implementation UIImage (GIF)

+ (UIImage *)sd_animatedGIFWithData:(NSData *)data {
    if (!data) {
        return nil;
    }

    //获取数据源
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)data, NULL);

    // 获取图片数量(如果传入的是gif图的二进制，那么获取的是图片帧数)
    size_t count = CGImageSourceGetCount(source);

    UIImage *animatedImage;

    if (count <= 1) {
        animatedImage = [[UIImage alloc] initWithData:data];
    }
    else {
        NSMutableArray *images = [NSMutableArray array];

        NSTimeInterval duration = 0.0f;

        for (size_t i = 0; i < count; i++) {
            CGImageRef image = CGImageSourceCreateImageAtIndex(source, i, NULL);

            duration += [self sd_frameDurationAtIndex:i source:source];

            [images addObject:[UIImage imageWithCGImage:image scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp]];

            CGImageRelease(image);
        }
    // 如果上面的计算播放时间方法没有成功，就按照下面方法计算
   // 计算一次播放的总时间：每张图播放1/10秒 * 图片总数
        if (!duration) {
            duration = (1.0f / 10.0f) * count;
        }

        animatedImage = [UIImage animatedImageWithImages:images duration:duration];
    }

    CFRelease(source);

    return animatedImage;
}
//**************************************
//计算每帧需要播放的时间
+ (float)sd_frameDurationAtIndex:(NSUInteger)index source:(CGImageSourceRef)source {
    float frameDuration = 0.1f;
    // 获取这一帧的属性字典
    CFDictionaryRef cfFrameProperties = CGImageSourceCopyPropertiesAtIndex(source, index, nil);
    NSDictionary *frameProperties = (__bridge NSDictionary *)cfFrameProperties;
    NSDictionary *gifProperties = frameProperties[(NSString *)kCGImagePropertyGIFDictionary];

    // 从字典中获取这一帧持续的时间
    NSNumber *delayTimeUnclampedProp = gifProperties[(NSString *)kCGImagePropertyGIFUnclampedDelayTime];
    if (delayTimeUnclampedProp) {
        frameDuration = [delayTimeUnclampedProp floatValue];
    }
    else {

        NSNumber *delayTimeProp = gifProperties[(NSString *)kCGImagePropertyGIFDelayTime];
        if (delayTimeProp) {
            frameDuration = [delayTimeProp floatValue];
        }
    }

    // Many annoying ads specify a 0 duration to make an image flash as quickly as possible.
    // We follow Firefox's behavior and use a duration of 100 ms for any frames that specify
    // a duration of <= 10 ms. See  and 
    // for more information.

    if (frameDuration < 0.011f) {
        frameDuration = 0.100f;
    }

    CFRelease(cfFrameProperties);
    return frameDuration;
}
//**************************************
+ (UIImage *)sd_animatedGIFNamed:(NSString *)name {
    CGFloat scale = [UIScreen mainScreen].scale;

    if (scale > 1.0f) {
        NSString *retinaPath = [[NSBundle mainBundle] pathForResource:[name stringByAppendingString:@"@2x"] ofType:@"gif"];

        NSData *data = [NSData dataWithContentsOfFile:retinaPath];

        if (data) {
            return [UIImage sd_animatedGIFWithData:data];
        }

        NSString *path = [[NSBundle mainBundle] pathForResource:name ofType:@"gif"];

        data = [NSData dataWithContentsOfFile:path];

        if (data) {
            return [UIImage sd_animatedGIFWithData:data];
        }

        return [UIImage imageNamed:name];
    }
    else {
        NSString *path = [[NSBundle mainBundle] pathForResource:name ofType:@"gif"];

        NSData *data = [NSData dataWithContentsOfFile:path];

        if (data) {
            return [UIImage sd_animatedGIFWithData:data];
        }

        return [UIImage imageNamed:name];
    }
}
//**************************************
/**
 1.取较大的缩放比例值，用这个值让宽高等比缩放
 2.调整位置，使缩放后的图居中
 3.遍历self.images， 将每张图缩放后导出，放到数组中
 4.使用上面的数组创建animatedImage并返回
 */
- (UIImage *)sd_animatedImageByScalingAndCroppingToSize:(CGSize)size {
    if (CGSizeEqualToSize(self.size, size) || CGSizeEqualToSize(size, CGSizeZero)) {
        return self;
    }

    CGSize scaledSize = size;
    CGPoint thumbnailPoint = CGPointZero;

    CGFloat widthFactor = size.width / self.size.width;
    CGFloat heightFactor = size.height / self.size.height;
    CGFloat scaleFactor = (widthFactor > heightFactor) ? widthFactor : heightFactor;
    scaledSize.width = self.size.width * scaleFactor;
    scaledSize.height = self.size.height * scaleFactor;

    if (widthFactor > heightFactor) {
        thumbnailPoint.y = (size.height - scaledSize.height) * 0.5;
    }
    else if (widthFactor < heightFactor) {
        thumbnailPoint.x = (size.width - scaledSize.width) * 0.5;
    }

    NSMutableArray *scaledImages = [NSMutableArray array];

    UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);

    for (UIImage *image in self.images) {
        [image drawInRect:CGRectMake(thumbnailPoint.x, thumbnailPoint.y, scaledSize.width, scaledSize.height)];
        UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

        [scaledImages addObject:newImage];
    }

    UIGraphicsEndImageContext();

    return [UIImage animatedImageWithImages:scaledImages duration:self.duration];
}

@end

三、拓展

下面的链接(http://www.cnblogs.com/Mike-zh/p/5205909.html)实现了其他关于Image的一些方法，包括：

1. NSData+ImageContentType: 根据NSData获取MIME
2. UIImage+GIF
3. UIImage+WebP
4. UIImage+MultiFormat:根据NSData相应的MIME将NSData转为UIImage
5. 方向处理