iOS开发中实现显示gif图片的方法

【 tulaoshi.com - 编程语言 】

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：
 

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
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：
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。