ios播放gif图片

以前一直听说ios不可以播放gif图片。也没取看看。其实想想有啥不能播放的。只是没有提供现成的api而已。最近看看资料以及别人的例子了解了一下实现原理 特记录一下：

gif 其实本来就是一系列的图片的集合 可以通过 imageIO 获取到图片数组。然后动画播放就ok了；先看一下 简单的例子：

NSURL *url = [[NSBundle mainBundle] URLForResource:@"pika.gif" withExtension:nil];
CGImageSourceRef csf = CGImageSourceCreateWithURL((__bridge CFTypeRef) url, NULL);
size_t const count = CGImageSourceGetCount(csf);
UIImage *frames[count];
CGImageRef images[count];
for (size_t i = 0; i < count; ++i) {
images[i] = CGImageSourceCreateImageAtIndex(csf, i, NULL);
UIImage *image =[[UIImage alloc] initWithCGImage:images[i]];
frames[i] = image;
CFRelease(images[i]);
}

UIImage *const animation = [UIImage animatedImageWithImages:[NSArray arrayWithObjects:frames count:count] duration:0.1];

[view2 setImage:animation];
NSLog(@"xxxx%zu",count);
CFRelease(csf);

一个简单的播放gif的例子就出来了。不过毫无疑问。这么写有很大的问题。原因在于gif 每一桢之间的间隔时间是可以设置的。甚至可以不同。所以需要做些处理

有个人的实现原理是这样的：取出gif图片所有桢的时间。 取这些时间的最大公约数 作为显示的的桢的时间。 然后根据新的桢的间隔时间取对应的图片。 这样处理显示的帧数大于等于原始帧数。 如果原始桢的间隔时间太奇葩。 会导致大量的图片是重复的。不过正常使用还是很不错的。

下面是 从code4app上下载的别人的代码 地址已经不记得了。删除了其他的部分 只留下了跟播放动画相关的地方 贴出来参考：

//
//  ViewController.m
//  test4
//
//  Created by Aurora_sgbh on 15-2-6.
//  Copyright (c) 2015年 Aurora_sgbh. All rights reserved.
//
#if __has_feature(objc_arc)
#define toCF (__bridge CFTypeRef)
#define fromCF (__bridge id)
#else
#define toCF (CFTypeRef)
#define fromCF (id)
#endif

#import "ViewController.h"
#import <ImageIO/ImageIO.h>
#pragma mark - UIImage Animated GIF

@implementation UIImage (animatedGIF)

static int delayCentisecondsForImageAtIndex(CGImageSourceRef const source, size_t const i) {
int delayCentiseconds = 1;
CFDictionaryRef const properties = CGImageSourceCopyPropertiesAtIndex(source, i, NULL);
if (properties) {
CFDictionaryRef const gifProperties = CFDictionaryGetValue(properties, kCGImagePropertyGIFDictionary);
if (gifProperties) {
NSNumber *number = fromCF CFDictionaryGetValue(gifProperties, kCGImagePropertyGIFUnclampedDelayTime);
if (number == NULL || [number doubleValue] == 0) {
number = fromCF CFDictionaryGetValue(gifProperties, kCGImagePropertyGIFDelayTime);
}
if ([number doubleValue] > 0) {
// Even though the GIF stores the delay as an integer number of centiseconds, ImageIO “helpfully” converts that to seconds for us.
delayCentiseconds = (int)lrint([number doubleValue] * 100);
NSLog(@"看看时间%d",delayCentiseconds);
}
}
CFRelease(properties);
}
return delayCentiseconds;
}

static void createImagesAndDelays(CGImageSourceRef source, size_t count, CGImageRef imagesOut[count], int delayCentisecondsOut[count]) {
for (size_t i = 0; i < count; ++i) {
imagesOut[i] = CGImageSourceCreateImageAtIndex(source, i, NULL);
delayCentisecondsOut[i] = delayCentisecondsForImageAtIndex(source, i);
}
}

static int sum(size_t const count, int const *const values) {
int theSum = 0;
for (size_t i = 0; i < count; ++i) {
theSum += values[i];
}
return theSum;
}

//最大公约数
static int pairGCD(int a, int b) {
if (a < b)
return pairGCD(b, a);
while (true) {
int const r = a % b;
if (r == 0)
return b;
a = b;
b = r;
}
}

static int vectorGCD(size_t const count, int const *const values) {
int gcd = values[0];
for (size_t i = 1; i < count; ++i) {
// Note that after I process the first few elements of the vector, `gcd` will probably be smaller than any remaining element.  By passing the smaller value as the second argument to `pairGCD`, I avoid making it swap the arguments.
gcd = pairGCD(values[i], gcd);
}
return gcd;
}

static NSArray *frameArray(size_t const count, CGImageRef const images[count], int const delayCentiseconds[count], int const totalDurationCentiseconds) {
int const gcd = vectorGCD(count, delayCentiseconds);
size_t const frameCount = totalDurationCentiseconds / gcd;
UIImage *frames[frameCount];
for (size_t i = 0, f = 0; i < count; ++i) {
UIImage *const frame = [UIImage imageWithCGImage:images[i]];
for (size_t j = delayCentiseconds[i] / gcd; j > 0; --j) {
frames[f++] = frame;
}
}
return [NSArray arrayWithObjects:frames count:frameCount];
}

static void releaseImages(size_t const count, CGImageRef const images[count]) {
for (size_t i = 0; i < count; ++i) {
CGImageRelease(images[i]);
}
}

//xxx
static UIImage *animatedImageWithAnimatedGIFImageSource(CGImageSourceRef const source) {
size_t const count = CGImageSourceGetCount(source);
CGImageRef images[count];
int delayCentiseconds[count]; // in centiseconds
createImagesAndDelays(source, count, images, delayCentiseconds);
int const totalDurationCentiseconds = sum(count, delayCentiseconds);
NSArray *const frames = frameArray(count, images, delayCentiseconds, totalDurationCentiseconds);
UIImage *const animation = [UIImage animatedImageWithImages:frames duration:(NSTimeInterval)totalDurationCentiseconds / 100.0];
releaseImages(count, images);
return animation;
}

static UIImage *animatedImageWithAnimatedGIFReleasingImageSource(CGImageSourceRef CF_RELEASES_ARGUMENT source) {
if (source) {
UIImage *const image = animatedImageWithAnimatedGIFImageSource(source);
CFRelease(source);
return image;
} else {
return nil;
}
}

+ (UIImage *)animatedImageWithAnimatedGIFData:(NSData *)data {
return animatedImageWithAnimatedGIFReleasingImageSource(CGImageSourceCreateWithData(toCF data, NULL));
}

+ (UIImage *)animatedImageWithAnimatedGIFURL:(NSURL *)url {
return animatedImageWithAnimatedGIFReleasingImageSource(CGImageSourceCreateWithURL((__bridge CFTypeRef) url, NULL));
}

@end

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
UIImageView *view =[[UIImageView alloc]initWithFrame:CGRectMake(50, 50, 100, 100)];

[view setImage:[UIImage animatedImageWithAnimatedGIFURL:[[NSBundle mainBundle] URLForResource:@"3.gif" withExtension:nil]]];

//mytest

//    UIImageView *view2 =[[UIImageView alloc]initWithFrame:CGRectMake(50, 250, 100, 100)];
//    [view2 setBackgroundColor:[UIColor redColor]];
//    NSURL *url = [[NSBundle mainBundle] URLForResource:@"pika.gif" withExtension:nil];
//    CGImageSourceRef csf = CGImageSourceCreateWithURL((__bridge CFTypeRef) url, NULL);
//    size_t const count = CGImageSourceGetCount(csf);
//    UIImage *frames[count];
//    CGImageRef images[count];
//    for (size_t i = 0; i < count; ++i) {
//        images[i] = CGImageSourceCreateImageAtIndex(csf, i, NULL);
//         UIImage *image =[[UIImage alloc] initWithCGImage:images[i]];
//        frames[i] = image;
//        CFRelease(images[i]);
//    }
//
//    UIImage *const animation = [UIImage animatedImageWithImages:[NSArray arrayWithObjects:frames count:count] duration:0.1];
//
//    [view2 setImage:animation];
//    NSLog(@"xxxx%zu",count);
//    CFRelease(csf);
//  [self.view addSubview:view2];

[self.view addSubview:view];

}

- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}

@end

另外也可以通过动画来播放。这样可能不会像上面出现特殊情况下大量重复的桢。不过现实中gif间隔一般都是固定的。所以上面就够用了。