在開發(fā)中我們有可能會遇到這樣的需求，在一個UIImageView來回切換倆張圖片來達到動態(tài)效果。我也是實驗了好久，后來經(jīng)過指導實現(xiàn)了，效果如下：

圖片來回切換.gif

iOS中定時器有三種：(1)NSTimer (2)CADisplayLink (3)dispatch_source,而我使用到的定時器是dispatch_source，下面就來看看代碼吧。（可以實現(xiàn)暫停和播放）

//初始化UIImageView
UIImage *img = [UIImage imageNamed:@"image_huoyan_1"];
backImage = [[UIImageView alloc] initWithFrame:CGRectMake(50, 60, self.view.frame.size.width/5, self.view.frame.size.width/5 * img.size.height/img.size.width)]; 
[backImage setImage:img];
[self.view addSubview:backImage];

//加載按鈕
self.button = [UIButton buttonWithType:UIButtonTypeCustom];
self.button.frame = CGRectMake(100, 300, 100, 100);
self.button.backgroundColor = [UIColor blueColor];
[self.button addTarget:self action:@selector(isAnimotion) forControlEvents:UIControlEventTouchUpInside]; 
[self.button setTitle:@"開始" forState:UIControlStateNormal];
[self.view addSubview:self.button];

//按鈕的點擊事件
-(void)isAnimotion {
    if([self.button.titleLabel.text isEqualToString:@"停止"]) {
        [self stopNS];
        [self.button setTitle:@"開始" forState:UIControlStateNormal];
    } else {
        [self startNS];
        [self.button setTitle:@"停止" forState:UIControlStateNormal];
    }
}

接下來就是主要代碼啦，其中需要注意的是：需要將dispatch_source_t timer設置為成員變量，不然會立即釋放。

@property (nonatomic, strong) dispatch_source_t timer;

//加載動畫
-(void)startNS {
    __block NSString *str =@"image_huoyan_2";
    backImage.image = [UIImage imageNamed:str];
    //定時器開始執(zhí)行的延時時間
    NSTimeInterval delayTime = 0.0f;
    //定時器間隔時間
    NSTimeInterval timeInterval = 0.1f;
    //創(chuàng)建子線程隊列
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    //使用之前創(chuàng)建的隊列來創(chuàng)建計時器
    _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    //設置延時執(zhí)行時間，delayTime為要延時的秒數(shù)
    dispatch_time_t startDelayTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayTime * NSEC_PER_SEC));
    //設置計時器
    dispatch_source_set_timer(_timer, startDelayTime, timeInterval * NSEC_PER_SEC, 0.1 * NSEC_PER_SEC);
    dispatch_source_set_event_handler(_timer, ^{
        //執(zhí)行事件
        if ( [str isEqualToString:@"image_huoyan_1"]) {
            str = @"image_huoyan_2";
        } else {
            str = @"image_huoyan_1";
        }
        dispatch_async(dispatch_get_main_queue(), ^{
            [backImage setImage:[UIImage imageNamed:str]];
        }) ;
    });
    // 啟動計時器
    dispatch_resume(_timer);
}

//停止動畫
-(void)stopNS {
    dispatch_source_cancel(_timer);
}

上面提到的"image_huoyan_1"和"image_huoyan_2"就是要用到的倆張圖片。寫的比較簡單，如果有錯誤請多多指教。