loading images from a background thread using blocks
I have the following method, which basically calls a request to load an array of NSData of images in the background thread:
[query findObjectsInBackgroundWithBlock:^(NSArray * objects, NSError * error){
}];
In this case objects is an array of the NSData. The issue is that if I have 100 images to load (100 elements in the array). This means that the user will have to wait for quite some time to see any image showing up in a UITableView. What I want to do is for th开发者_如何学Pythonem to see an image once it is available/loaded.. do I have to then change the code so that it does 100 background threads to load the image?
you could implement something like this in your cellForRowAtIndexPath:
That way you load each image in the background and as soon as its loaded the corresponding cell is updated on the mainThread.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^(void) {
NSData *data0 = [NSData dataWithContentsOfURL:someURL];
UIImage *image = [UIImage imageWithData:data0];
dispatch_sync(dispatch_get_main_queue(), ^(void) {
UIImageView* imageView = (UIImageView*)[cell viewWithTag:100];
imageView.image = image;
});
});
You can create NSInvocationOperation
and set it to NSOperationQueue
for example:
Initializing NSOperationQueue
:
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
After create NSInvocationOperation
:
NSInvocationOperation* downloadOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(selectorToDownloadImage:) object:YouData];
[operationQueue addOperation:downloadOperation];
[downloadOperation release];
No, you don't have to create that many background threads. Use NSOperationQueue
.
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