iOS Downloading image in background and updating the UI - ios

Question

I am trying update an imageview with new image for every 1 sec by downloading the image from the server. The downloading happens in background thread. Below shown is the code
NSTimer *timer = [NSTimer timerWithTimeInterval:0.5
target:self
selector:#selector(timerFired:)
userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
-(void)timerFired:(id)sender
{
NSURLRequest *request=[[NSURLRequest alloc]initWithURL:[NSURL
URLWithString:#"http://192.168.4.116:8080/RMC/ImageWithCommentData.jpg"]];
NSOperationQueue *queueTmp = [[NSOperationQueue alloc] init];
[NSURLConnection sendAsynchronousRequest:request queue:queueTmp completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
if ([data length] > 0 && error == nil)
{
[self performSelectorOnMainThread:#selector(processImageData:) withObject:data waitUntilDone:TRUE modes:nil];
}
else if ([data length] == 0 && error == nil)
{
}
else if (error != nil)
{
}
}];
}
-(void)processImageData:(NSData*)imageData
{
NSLog(#"data downloaded");
[self.hmiImageView setImage:[UIImage imageWithData:imageData]];
}
My image is getting downloaded. But ProcessImageData method is not called. Please help me to fix this issue.

Answer 1

The problem is you are calling NSURLConnection asynchronously :
[NSURLConnection sendAsynchronousRequest:request queue:queueTmp completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
so before you get any data the : if ([data length] > 0 && error == nil) get called .
so the data length remains 0 thats why your method is not called . for achieving your requirement you can do like :
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^(void) {
NSData *imageData = //download image here
UIImage* image = [[UIImage alloc] initWithData:imageData];
if (image) {
dispatch_async(dispatch_get_main_queue(), ^{
//set image here
}
});
}
});