IOS中如何解析並顯示Gif

IOS中如何解析並顯示Gif

　　聊天的時候我們經常用到很多搞笑的Gif表情，有時候千言萬語真的比不上一個Gif來的實在。以前一直以為想Gif作為一種常用格式，各大平台應該都會支援，知道前兩天項目中要載入一個Gif作為過渡動畫，我查了半天協助文檔，發現IOS中居然沒有現成的支援載入和播放Gif的類。

　　於是上網簡單的搜了一下，發現兩個比較有有用的代碼。網址分別如下：

      三種方式顯示GIF圖片

　　andrei512 / GIFLoader.h

　　這兩種方法都是採用ImageIO庫，對Gif檔案進行解析，然後自己做動畫顯示，至此顯示Gif動畫的思路就已經比較明確了。

　　我們知道Gif是由一陣陣畫面組成的，而且每一幀畫面播放的時常可能會不相等，觀察上面兩個例子，發現他們都沒有對Gif中每一幀的顯示時常做處理，這樣的結果就是整個Gif中每一幀畫面都是以固定的速度向前播放，很顯然這並不總會符合需求。

　　於是自己寫一個解析Gif的工具類，解決每一幀畫面並遵循每一幀所對應的顯示時間進行播放。

　　程式的思路如下：

　　1、首先使用ImageIO庫中的CGImageSource家在Gif檔案。

　　2、通過CGImageSource擷取到Gif檔案中的總的幀數，以及每一幀的顯示時間。

　　3、通過CAKeyframeAnimation來完成Gif動畫的播放。

　　下面直接上我寫的解析和播放Gif的工具類的代碼：

SvGifView

////  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

////  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值是一樣的        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

　　代碼很短也比較容易，就不一一解釋了。最開始的那個C函數主要就是用來解析Gif的，之所以用C函數是因為我要返回多個資訊，而Objective-c只能返回一個參數，而且Objective-c和C語言可以很方便的混合編程。

 　　測試程式Github地址：https://github.com/smileEvday/SvGifView/