Iphone 淡入淡出图像时的计时困难

我试图有三个图像淡入淡出一次一个。我想我已经非常熟悉这段代码了，但它并没有像我预期的那样工作

我所希望的是，每个图像将在0.5秒内淡入，然后在屏幕上保持2秒，然后在0.5秒内淡出。一旦第三个图像消失，我希望它停止

下面的代码一次又一次地淡出第一幅图像，我似乎无法正确地确定时间。任何帮助都会很好

-(void) viewDidLoad {

    pImageC = [[UIImageView alloc]init];
    NSArray *animationArray = [NSArray arrayWithObjects:[UIImage 
    imageNamed:@"p_image_a.png"],[UIImage imageNamed:@"p_image_b.png"],[UIImage 
    imageNamed:@"p_image_c.png"], nil]; //add your images here
    [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(crossfade) 
    userInfo:nil repeats:YES];
    [pImageC  setFrame:CGRectMake(0,0,320,367)];
    pImageC.animationImages = animationArray; //mainImageView is   imageview
    pImageC.animationDuration = 2;
    pImageC.animationRepeatCount = 0;
    [pImageC startAnimating];
    [self.view addSubview:pImageC];
}

- (void)crossfade {

    [UIView animateWithDuration:0.5 delay:0.0 options:UIViewAnimationOptionCurveEaseInOut 
    animations:^{
        pImageC.alpha = !pImageC.alpha;
    }completion:^(BOOL done){
        //
    }];
}

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对于交叉淡入淡出动画，请尝试类似的方法

- (void)crossfade 
{
    [UIView animateWithDuration:0.3 delay:0.0 options:UIViewAnimationOptionCurveEaseInOut animations:^{
        self.animationImageView.alpha = 0.0;
    }completion:^(BOOL done){
        [self performAnimationOnView];

        [UIView animateWithDuration:0.3 delay:0.0 options:UIViewAnimationOptionCurveEaseIn animations:^{
            self.animationImageView.alpha = 1.0;
        }completion:^(BOOL done){


        }];


    }];

}

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你的pImageC.alpha=！pImageC.alpha；毫无意义。alpha是一个浮点值，而不是布尔值。