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：
- 使用ImageIO库中的CGImageSource获取数据源
-
CGImageSourceGetCount获取GIF图片的数量，并计算出每一张图显示的时间 - 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 <UIKit/UIKit.h>
@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 <ImageIO/ImageIO.h>
@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 <rdar://problem/7689300> and <http://webkit.org/b/36082>
// 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：
- NSData+ImageContentType: 根据NSData获取MIME
- UIImage+GIF
- UIImage+WebP
- UIImage+MultiFormat:根据NSData相应的MIME将NSData转为UIImage
- 方向处理
