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, 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。

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(50,50,0,0);

    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。