Navigating to a different view - pushViewController - iphone

Question

I have a tableview, and when i click on a row, it navigates to another view; The code for the navigation part is shown below;
ShowImageController *showImageController = [[HowItWorksViewController alloc] initWithNibName:nil bundle:nil];
[self.navigationController pushViewController:showImageController animated:YES];
The other view contains an image, i have added the image to its viewDidLoad. and here's the code for that
UIImageView *imageView=[[UIImageView alloc] initWithImage:[UIImage imageNamed:#"hello.png"]];
[imageView setFrame:CGRectMake(o, o, 200, 300)];
[[self view] addSubview:imageView ];
The problem is When i click on the row it takes a long time (extremely slow), to navigate to the other screen.
note: Rows which didn't have an image in the other view navigated well with no issue. Why is this happening ? and how can i fix it ?

Answer 1

Try loading the images in a asynk task or nsoperationqueue :)

Answer 2

Definitely sounds like the images are big and therefore taking a while to load. I suggest you either use smaller images or if you have no control over them you might want to try loading the images in the background. Here is some code to get you started with loading them in the background:
- (void)decodeImageInBackgroundThread:(UIImage*)decodedImage forImageView:(UIImageView*)imageView {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
CGImageRef originalImage = [decodedImage CGImage];
CFDataRef imageData = CGDataProviderCopyData(CGImageGetDataProvider(originalImage));
CGDataProviderRef imageDataProvider = CGDataProviderCreateWithCFData(imageData);
if (imageData != NULL) {
CFRelease(imageData);
}
CGImageRef image = CGImageCreate(CGImageGetWidth(originalImage),
CGImageGetHeight(originalImage),
CGImageGetBitsPerComponent(originalImage),
CGImageGetBitsPerPixel(originalImage),
CGImageGetBytesPerRow(originalImage),
CGImageGetColorSpace(originalImage),
CGImageGetBitmapInfo(originalImage),
imageDataProvider,
CGImageGetDecode(originalImage),
CGImageGetShouldInterpolate(originalImage),
CGImageGetRenderingIntent(originalImage));
if (imageDataProvider != NULL) {
CGDataProviderRelease(imageDataProvider);
}
dispatch_async(dispatch_get_main_queue(), ^{
[imageView setImage:[UIImage imageWithCGImage:image]];
CGImageRelease(image);
});
});
}
Which you can then use like this:
- (void)viewDidLoad {
...
UIImage *image = [UIImage imageNamed:#"hello.png"];
UIImageView *imageView = [[UIImageView alloc] initWithImage:nil];
[imageView setFrame:CGRectMake(0.0f, 0.0f, 200.0f, 300.0f)];
[[self view] addSubview:imageView];
[self decodeImageInBackgroundThread:image forImageView:imageView];
}