在执行startAnimating时UIImageView动画延迟

Question

我有一个21帧的菜单背景动画.我使用视图的viewDidLoad方法中的以下代码将它们加载到内存中.

NSMutableArray *menuanimationImages = [[NSMutableArray alloc] init];

for( int aniCount = 0; aniCount < 21; aniCount++ )
{

    NSString *fileLocation = [[NSBundle mainBundle] pathForResource: [NSString stringWithFormat: @"bg%i", aniCount + 1] ofType: @"png"];
    NSData *imageData = [NSData dataWithContentsOfFile: fileLocation];

    [menuanimationImages addObject: [UIImage imageWithData:imageData]];

}

settingsBackground.animationImages = menuanimationImages;

不幸的是,做[settingsBackground startAnimating]; 在viewDidLoad方法中不起作用.有没有办法预加载动画,所以第一次运行没有1-3秒的延迟？

Answer 1

我通常不建议使用imageNamed并依赖于内置的缓存机制.如果你搜索,你会发现很多关于这个问题的讨论,但它也不一定会预渲染你的图像.

我使用以下代码预加载和预渲染图像,以便在第一次动画时没有延迟.

NSMutableArray *menuanimationImages = [[NSMutableArray alloc] init];

for (int aniCount = 1; aniCount < 21; aniCount++) {
    NSString *fileLocation = [[NSBundle mainBundle] pathForResource: [NSString stringWithFormat: @"bg%i", aniCount + 1] ofType: @"png"];
    // here is the code to pre-render the image
    UIImage *frameImage = [UIImage imageWithContentsOfFile: fileLocation];
    UIGraphicsBeginImageContext(frameImage.size);
    CGRect rect = CGRectMake(0, 0, frameImage.size.width, frameImage.size.height);
    [frameImage drawInRect:rect];
    UIImage *renderedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    [menuanimationImages addObject:renderedImage];
}

settingsBackground.animationImages = menuanimationImages;