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，很顯然這并不總會符合需求。
于是自己寫一個解析Gif的工具類，解決每一幀畫面并遵循每一幀所對應的顯示時間進行播放。
程序的思路如下：
1、首先使用ImageIO庫中的CGImageSource家在Gif文件。
2、通過CGImageSource獲取到Gif文件中的總的幀數，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.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信息，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。
另外再介紹兩種使用UIImageView的方法：
1. 使用UIWebView播放
// 設定位置和大小
CGRect frame = CGRectMake(50,50,0,0);
frame.size = [UIImage imageNamed:@"guzhang.gif"].size;
// 讀取gif圖片數據
NSData *gif = [NSData dataWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"guzhang" ofType:@"gif"]];
// view生成
UIWebView *webView = [[UIWebView alloc] initWithFrame:frame];
webView.userInteractionEnabled = NO;//用戶不可交互
[webView loadData:gif MIMEType:@"image/gif" textEncodingName:nil baseURL:nil];
[self.view addSubview:webView];
[webView release];
2.將gif圖片分解成多張png圖片，使用UIImageView播放。
代碼如下：
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; //動畫圖片數組
gifImageView.animationDuration = 5; //執行一次完整動畫所需的時長
gifImageView.animationRepeatCount = 1; //動畫重復次數
[gifImageView startAnimating];
[self.view addSubview:gifImageView];
[gifImageView release];
注意：這個方法，如果gif動畫每楨間的時間間隔不同，不能達到此效果。
