How to avoid twice adding UIView on not ended block? - ios

Question

I have a "loading" view added to an uiimageview to indicate the image is being loaded, then on a dispatch async I am charging the image and removing the "loading" view once it has finished, problem is that if I call twice this method the "loading" view is added twice and the second one is never removed.
Edited:
on view.h
UIView *loading;
on view.m
loading = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];
loading.backgroundColor = [UIColor blackColor];
loading.alpha = 0.8;
loading.layer.cornerRadius = 10;
loading.center = CGPointMake(imageView.frame.size.width/2, imageView.frame.size.height/2);
if (![imageView.subviews containsObject:loading]) {
[imageView addSubview:loading];
}
dispatch_queue_t downloadFoto = dispatch_queue_create("Get Photo", NULL);
dispatch_async(downloadFoto, ^{
UIImage *image = [[UIImage alloc]initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[selectedImage objectForKey:#"url"]]]];
dispatch_sync(dispatch_get_main_queue(), ^{
if (image) {
[imageView setImage:image];
[imageView setNeedsLayout];
if ([imageView.subviews containsObject:loading]) {
[loading removeFromSuperview];
}
}
});
});
If this is called just once or if I call it after the loading is already removed everything works fine, the problem is if I call this before the block had finished.
Thank you guys, this is my solution at the end.
if (!blackView) {
UIActivityIndicatorView *load = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
blackView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];
blackView.backgroundColor = [UIColor blackColor];
blackView.alpha = 0.8;
blackView.layer.cornerRadius = 10;
blackView.center = CGPointMake(fotoVisual.frame.size.width/2, fotoVisual.frame.size.height/2);
load.center = CGPointMake(blackView.frame.size.width/2, blackView.frame.size.height/2);
[load startAnimating];
[blackView addSubview:load];
[fotoVisual setImage:[UIImage imageNamed:#"previewImagen.png"]];
descripcionFotoView.text = [selectedImage objectForKey:#"titulo"];
}
if (![fotoVisual.subviews containsObject:blackView]) {
[fotoVisual addSubview:blackView];
}
dispatch_queue_t downloadFoto = dispatch_queue_create("Get Photo", NULL);
dispatch_async(downloadFoto, ^{
[fotoVisual setImageWithURL:[NSURL URLWithString:[selectedImage objectForKey:#"url"]]
placeholderImage:[UIImage imageNamed:#"previewImagen.png"]];
dispatch_async(dispatch_get_main_queue(), ^{
[blackView removeFromSuperview];
blackView = nil;
});
});
dispatch_release(downloadFoto);

Answer 1

It looks like the issue you have is that you are creating a new loading view each time, which is not what you want. Your [imageView.subviews containsObject:loading] will never be true as you make a new loading view each time.
You could change the creation logic to do the checking like this
if (!loading) {
// configure loading
[imageView addSubview:loading];
}
Then modify your call back to something like
dispatch_sync(dispatch_get_main_queue(), ^{
if (image) {
[imageView setImage:image];
[imageView setNeedsLayout];
[loading removeFromSuperview];
loading = nil;
}
});
Is there any specific reason you are using dispatch_sync instead of dispatch_async?

Answer 2

Add you loading subview in dispatch_async block
dispatch_queue_t downloadFoto = dispatch_queue_create("Get Photo", NULL);
dispatch_async(downloadFoto, ^{
if (!loading.superview) {
// we assume your loading view doesn't have a superview so we can add it to imageView
dispatch_sync(dispatch_get_main_queue(), ^{
[imageView addSubview:loading];
};
}
UIImage *image = [[UIImage alloc]initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[selectedImage objectForKey:#"url"]]]];
if (image) {
dispatch_sync(dispatch_get_main_queue(), ^{
[imageView setImage:image];
[imageView setNeedsLayout];
if ([imageView.subviews containsObject:loading]) {
[loading removeFromSuperview];
}
});
}
});
For Async image downloading you can also use SDWebimage
Just download the project and add SDWebimage folder to your project and use as folows
#import "UIImageView+WebCache.h"
[self.imageView setImageWithURL:[NSURL URLWithString:[selectedImage objectForKey:#"url"]]
placeholderImage:[UIImage imageNamed:#"placeholder.png"]];
This will also cache the image.