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：
// // 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
// 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：
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。
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