iOS开发中实现显示gif图片的方法

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：

复制代码代码如下:

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

#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.
//

#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,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,_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);

    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。

另外再介绍两种使用UIImageView的方法：

1. 使用UIWebView播放

复制代码代码如下:

    // 设定位置和大小
    CGRect frame = CGRectMake(50,50,0);
    frame.size = [UIImage imageNamed:@"guzhang.gif"].size;
    // 读取gif图片数据
    NSData *gif = [NSData dataWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"guzhang" ofType:@"gif"]];
    // view生成
    UIWebView *webView = [[UIWebView alloc] initWithFrame:frame];
    webView.userInteractionEnabled = NO;//用户不可交互
    [webView loadData:gif MIMEType:@"image/gif" textEncodingName:nil baseURL:nil];
    [self.view addSubview:webView];
    [webView release];

2.将gif图片分解成多张png图片，使用UIImageView播放。
代码如下：

复制代码代码如下:

UIImageView *gifImageView = [[UIImageView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    NSArray *gifArray = [NSArray arrayWithObjects:[UIImage imageNamed:@"1"],
                                                  [UIImage imageNamed:@"2"],
                                                  [UIImage imageNamed:@"3"],
                                                  [UIImage imageNamed:@"4"],
                                                  [UIImage imageNamed:@"5"],
                                                  [UIImage imageNamed:@"6"],
                                                  [UIImage imageNamed:@"7"],
                                                  [UIImage imageNamed:@"8"],
                                                  [UIImage imageNamed:@"9"],
                                                  [UIImage imageNamed:@"10"],
                                                  [UIImage imageNamed:@"11"],
                                                  [UIImage imageNamed:@"12"],
                                                  [UIImage imageNamed:@"13"],
                                                  [UIImage imageNamed:@"14"],
                                                  [UIImage imageNamed:@"15"],
                                                  [UIImage imageNamed:@"16"],
                                                  [UIImage imageNamed:@"17"],
                                                  [UIImage imageNamed:@"18"],
                                                  [UIImage imageNamed:@"19"],
                                                  [UIImage imageNamed:@"20"],
                                                  [UIImage imageNamed:@"21"],
                                                  [UIImage imageNamed:@"22"],nil];
    gifImageView.animationImages = gifArray; //动画图片数组
    gifImageView.animationDuration = 5; //执行一次完整动画所需的时长
    gifImageView.animationRepeatCount = 1; //动画重复次数
    [gifImageView startAnimating];
    [self.view addSubview:gifImageView];
    [gifImageView release];

注意：这个方法，如果gif动画每桢间的时间间隔不同，不能达到此效果。

iOS开发中实现显示gif图片的方法

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