UIImageView动画预加载

Question

I've been battling for a few days trying to get the most effective/efficient solution to load an array of images to the .animationImages properties and be able to change that array on the fly. Here is the scenario: - I have one UIImageView - Depending on user input (phone movement, gyro) I will load a specific array of images to animate. - On user input (touch) play the animation loaded.

Now, the array of images is loaded on a different thread using "NSThread detachNewThreadSelector" called from the block ran on the gyroHandler (only on certain cases) using the initWithData. Other initiation methods were a complete fail.

Now the issue is that when I touch for the first time (since the current animation has been loaded) and triggers the animation the whole thing freezes for aprox. one second and then plays the animation. If I touch again it plays the animation successfully with no delay/freeze.

Now i read somewhere to animate in the background... I tried using:

[imgAnimationKey performSelectorInBackground:@selector(startAnimating) withObject:nil];

but the outcome was the same.

My array has 19 images and most likely will have the same always. Problem is I might have more 5+ animations that could play that is why I dont have multiple UIImageViews.

Anybody knows a way to preload the images and avoid the delay on first play? Or can I make the animation to run in a different thread and avoid this effect (I might be doing it wrong)?

Thanks!

Answer 1

You could make a category for the UIImage class for preloading your image in a background thread before you provide it to the image property of your UIImageView:

h:

#import <Foundation/Foundation.h>

@interface UIImage (preloadedImage)

- (UIImage *) preloadedImage;

@end

m:

#import "UIImage+preloadedImage.h"

@implementation UIImage (preloadedImage)

- (UIImage *) preloadedImage {
    CGImageRef image = self.CGImage;

    // make a bitmap context of a suitable size to draw to, forcing decode
    size_t width = CGImageGetWidth(image);
    size_t height = CGImageGetHeight(image);

    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef imageContext =  CGBitmapContextCreate(NULL, width, height, 8, width * 4, colourSpace,
                                                       kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little);
    CGColorSpaceRelease(colourSpace);

    // draw the image to the context, release it
    CGContextDrawImage(imageContext, CGRectMake(0, 0, width, height), image);

    // now get an image ref from the context
    CGImageRef outputImage = CGBitmapContextCreateImage(imageContext);

    UIImage *cachedImage = [UIImage imageWithCGImage:outputImage];

    // clean up
    CGImageRelease(outputImage);
    CGContextRelease(imageContext);

    return cachedImage;
}

@end

make the call of the preloadedImage on a background thread then and set the result on the main thread.