Preloading a UIImageView animation using objective

问题:

I have an animated image which works great. It consists of 180 high quality images and it plays fine and loops continuously. My problem is that the first time I load the view containing these images it takes a long time to load. Every subsequent time after that it loads immediately as I am assuming that the images have been cached or preloaded!!! I come from a flash background and as I am sure you aware preloaders are as common as muck so I don't feel this should be difficult to find but after countless googling I cannot find any good examples on preloading or any articles on why there is a delay and what to do about it.

So my question(s) is this:

1. Is there a checkbox in the info.plist to preload all my images at the start of the app?

2. How can you preload images and are there any simple example projects that I could look at?

3. Is this the best way to implement what is essentially a video but has been output to a png sequence?

4. Is there another method as viewDidLoad does not work as I expect it to do. It traces "FINISHED LOADING IMAGES" (see code below) but the view does not show for a second or two after the images have been loaded so if the view does not show until the images have loaded then neither will the UIActivityIndicatorView which is also in the same view.

5. How do you do event listening in objective c?

Below is the code in the viewDidLoad which I believe is fairly standard:

Any help is greatly appreciated as I am banging my head on a brick wall on something that seems so basic in ui development. Help :)

- (void)viewDidLoad {
    [super viewDidLoad];

    imageArray = [[NSMutableArray alloc] initWithCapacity:IMAGE_COUNT];

    NSLog(@"START LOADING IMAGES");

    // Build array of images, cycling through image names
    for (int i = 0; i < IMAGE_COUNT; i++){
        [imageArray addObject:[UIImage imageNamed: [NSString stringWithFormat:@"Main_%d.png", i]]];
    }

    animatedImages = [[UIImageView alloc] initWithFrame:CGRectMake(0,20,IMAGE_WIDTH, IMAGE_HEIGHT)];
    animatedImages.animationImages = [NSArray arrayWithArray:imageArray];
    animatedImages.animationDuration = 6.0;
    animatedImages.animationRepeatCount = 0;    
    [self.view addSubview:animatedImages];
    animatedImages.startAnimating;
    [animatedImages release];

    NSLog(@"FINISH LOADING IMAGES");

} 

Cheers

M

回答1:

In case someone finds this question, I have an answer, which is to pre-render the images like this.

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 load and 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();

    // then add the resulting image to the array
    [menuanimationImages addObject:renderedImage];
}

settingsBackground.animationImages = menuanimationImages;

I have tried multiple other methods of pre-loading images, and this is the only thing I've found that works.

回答2:

My problem is that the first time I load the view containing these images it takes a long time to load. Every subsequent time after that it loads immediately as I am assuming that the images have been cached or preloaded

you are right at this point ...... as you are using method imageNamed: for this method document quotes.....

This method looks in the system caches for an image object with the specified name and returns that object if it exists. If a matching image object is not already in the cache, this method loads the image data from the specified file, caches it, and then returns the resulting object.

so in my opinion, rather than doing following stuff in viewDidLoad, you should do it earlier where delay is of not considerable......

    for (int i = 0; i < IMAGE_COUNT; i++)
    { 
    [imageArray addObject:[UIImage imageNamed: [NSString stringWithFormat:@"Main_%d.png", i]]]; 
}

another approach

- (void)spinLayer:(CALayer *)inLayer duration:(CFTimeInterval)inDuration
        direction:(int)direction
{
    CABasicAnimation* rotationAnimation;

    // Rotate about the z axis
    rotationAnimation = 
    [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];

    // Rotate 360 degress, in direction specified
    rotationAnimation.toValue = [NSNumber numberWithFloat: M_PI * 2.0 * direction];

    // Perform the rotation over this many seconds
    rotationAnimation.duration = inDuration;
    rotationAnimation.repeatCount = 100;
    //rotationAnimation.

    // Set the pacing of the animation
    //rotationAnimation.timingFunction = 
    [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];

    // Add animation to the layer and make it so
    [inLayer addAnimation:rotationAnimation forKey:@"rotationAnimation"];
}

this method will help in animation call it as follow(I am assuming that you are putting above method in same class where you have imageView.

[self spinLayer:yourImageView.layer duration:5.0
            direction:<-1 or 1 for anti clockwise or clockwise spin>];

remember just set only one image to that imageView(which you wish to animate. thanks,