IOS中如何解析并显示Gif

IOS中如何解析并显示Gif

　　聊天的时候我们经常用到很多搞笑的Gif表情，有时候千言万语真的比不上一个Gif来的实在。以前一直以为想Gif作为一种常用格式，各大平台应该都会支持，知道前两天项目中要加载一个Gif作为过渡动画，我查了半天帮助文档，发现IOS中居然没有现成的支持加载和播放Gif的类。

　　于是上网简单的搜了一下，发现两个比较有有用的代码。网址分别如下：

      三种方式显示GIF图片

　　andrei512 / GIFLoader.h

　　这两种方法都是采用ImageIO库，对Gif文件进行解析，然后自己做动画显示，至此显示Gif动画的思路就已经比较明确了。

　　我们知道Gif是由一阵阵画面组成的，而且每一帧画面播放的时常可能会不相等，观察上面两个例子，发现他们都没有对Gif中每一帧的显示时常做处理，这样的结果就是整个Gif中每一帧画面都是以固定的速度向前播放，很显然这并不总会符合需求。

　　于是自己写一个解析Gif的工具类，解决每一帧画面并遵循每一帧所对应的显示时间进行播放。

　　程序的思路如下：

　　1、首先使用ImageIO库中的CGImageSource家在Gif文件。

　　2、通过CGImageSource获取到Gif文件中的总的帧数，以及每一帧的显示时间。

　　3、通过CAKeyframeAnimation来完成Gif动画的播放。

　　下面直接上我写的解析和播放Gif的工具类的代码：

//
//  SvGifView.h
//  SvGifSample
//
//  Created by maple on 3/28/13.
//  Copyright (c) 2013 smileEvday. All rights reserved.
//
//  QQ: 1592232964


#import <UIKit/UIKit.h>

@interface SvGifView : UIView


/*
 * @brief desingated initializer
 */
- (id)initWithCenter:(CGPoint)center fileURL:(NSURL*)fileURL;

/*
 * @brief start Gif Animation
 */
- (void)startGif;

/*
 * @brief stop Gif Animation
 */
- (void)stopGif;

/*
 * @brief get frames image(CGImageRef) in Gif
 */
+ (NSArray*)framesInGif:(NSURL*)fileURL;


@end

//
//  SvGifView.m
//  SvGifSample
//
//  Created by maple on 3/28/13.
//  Copyright (c) 2013 smileEvday. All rights reserved.
//
//  QQ: 1592232964

#import "SvGifView.h"
#import <ImageIO/ImageIO.h>
#import <QuartzCore/CoreAnimation.h>

/*
 * @brief resolving gif information
 */
void getFrameInfo(CFURLRef url, NSMutableArray *frames, NSMutableArray *delayTimes, CGFloat *totalTime,CGFloat *gifWidth, CGFloat *gifHeight)
{
    CGImageSourceRef gifSource = CGImageSourceCreateWithURL(url, NULL);
    
    // get frame count
    size_t frameCount = CGImageSourceGetCount(gifSource);
    for (size_t i = 0; i < frameCount; ++i) {
        // get each frame
        CGImageRef frame = CGImageSourceCreateImageAtIndex(gifSource, i, NULL);
        [frames addObject:(id)frame];
        CGImageRelease(frame);
        
        // get gif info with each frame
        NSDictionary *dict = (NSDictionary*)CGImageSourceCopyPropertiesAtIndex(gifSource, i, NULL);
        NSLog(@"kCGImagePropertyGIFDictionary %@", [dict valueForKey:(NSString*)kCGImagePropertyGIFDictionary]);
        
        // get gif size
        if (gifWidth != NULL && gifHeight != NULL) {
            *gifWidth = [[dict valueForKey:(NSString*)kCGImagePropertyPixelWidth] floatValue];
            *gifHeight = [[dict valueForKey:(NSString*)kCGImagePropertyPixelHeight] floatValue];
        }
        
        // kCGImagePropertyGIFDictionary中kCGImagePropertyGIFDelayTime，kCGImagePropertyGIFUnclampedDelayTime值是一样的
        NSDictionary *gifDict = [dict valueForKey:(NSString*)kCGImagePropertyGIFDictionary];
        [delayTimes addObject:[gifDict valueForKey:(NSString*)kCGImagePropertyGIFDelayTime]];
        
        if (totalTime) {
            *totalTime = *totalTime + [[gifDict valueForKey:(NSString*)kCGImagePropertyGIFDelayTime] floatValue];
        }
    }
}

@interface SvGifView() {
    NSMutableArray *_frames;
    NSMutableArray *_frameDelayTimes;
    
    CGFloat _totalTime;         // seconds
    CGFloat _width;
    CGFloat _height;
}

@end

@implementation SvGifView


- (id)initWithCenter:(CGPoint)center fileURL:(NSURL*)fileURL;
{
    self = [super initWithFrame:CGRectZero];
    if (self) {
        
        _frames = [[NSMutableArray alloc] init];
        _frameDelayTimes = [[NSMutableArray alloc] init];
        
        _width = 0;
        _height = 0;
        
        if (fileURL) {
            getFrameInfo((CFURLRef)fileURL, _frames, _frameDelayTimes, &_totalTime, &_width, &_height);
        }
        
        self.frame = CGRectMake(0, 0, _width, _height);
        self.center = center;
    }
    
    return self;
}

+ (NSArray*)framesInGif:(NSURL *)fileURL
{
    NSMutableArray *frames = [NSMutableArray arrayWithCapacity:3];
    NSMutableArray *delays = [NSMutableArray arrayWithCapacity:3];
    
    getFrameInfo((CFURLRef)fileURL, frames, delays, NULL, NULL, NULL);
    
    return frames;
}

- (void)startGif
{
    CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"contents"];
    
    NSMutableArray *times = [NSMutableArray arrayWithCapacity:3];
    CGFloat currentTime = 0;
    int count = _frameDelayTimes.count;
    for (int i = 0; i < count; ++i) {
        [times addObject:[NSNumber numberWithFloat:(currentTime / _totalTime)]];
        currentTime += [[_frameDelayTimes objectAtIndex:i] floatValue];
    }
    [animation setKeyTimes:times];
    
    NSMutableArray *images = [NSMutableArray arrayWithCapacity:3];
    for (int i = 0; i < count; ++i) {
        [images addObject:[_frames objectAtIndex:i]];
    }
    
    [animation setValues:images];
    [animation setTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear]];
    animation.duration = _totalTime;
    animation.delegate = self;
    animation.repeatCount = 5;
    
    [self.layer addAnimation:animation forKey:@"gifAnimation"];
}

- (void)stopGif
{
    [self.layer removeAllAnimations];
}

// remove contents when animation end
- (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag
{
    self.layer.contents = nil;
}

// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    // Drawing code
}


@end

　　代码很短也比较容易，就不一一解释了。最开始的那个C函数主要就是用来解析Gif的，之所以用C函数是因为我要返回多个信息，而Objective-c只能返回一个参数，而且Objective-c和C语言可以很方便的混合编程。

 　　测试程序Github地址：https://github.com/smileEvday/SvGifView/