How to implement lazy loading to uiscroll view - iphone

Question

How to implement lazy loading to uiscroll view
I am taking 15 images from the web service and add it to UIscrollview
I want to lad the scroll view with temporary image and when the image is ready it can add the image to uiscrollview
-(void)loadthscroll:(NSMutableArray *)idarray:(NSMutableArray *)imgarray
{
/*************scroll for scroll in in theater******************/
scrollview_intheater= [[UIScrollView alloc] initWithFrame:CGRectMake(0, btn_thhead.frame.size.height,view_banner.frame.size.width, view_intheater.frame.size.height-btn_thhead.frame.size.height)];
[view_intheater addSubview:scrollview_intheater];
[scrollview_thcsoon removeFromSuperview];
adj=5;
currentx=5;
for(int i=0;i<[imgarray count];i++)
{
btn_theater_ct = [UIButton buttonWithType:UIButtonTypeCustom];
btn_theater_ct.frame=CGRectMake(currentx, 5, 95, 120);
[btn_theater_ct addTarget:self action:#selector(theaterAction:) forControlEvents:UIControlEventTouchDown];
[scrollview_intheater addSubview:btn_theater_ct];
addr = [imgarray objectAtIndex:i];
addr = [addr stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding];
//NSLog(#"addr-------%#",addr);
data_theater = [NSData dataWithContentsOfURL:[NSURL URLWithString:addr ] ];
[btn_theater_ct setBackgroundImage:[UIImage imageWithData:data_theater] forState:UIControlStateNormal];
currentx +=btn_theater_ct.frame.size.width+adj;
btn_theater_ct.tag=i;
[scrollview_intheater setContentSize:CGSizeMake(currentx,0)];
NSLog(#"add th scroll--%d----%d",[imgarray count],i);
}
}

Answer 1

I face the same issue before few days but i fixed it now by
importing
#import "UIImageView+AFNetworking.h"
and implementing its method
- (void)setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholderImage;
to use this u have to use AFNetworking class

Answer 2

Set up the whole UIScrollView with a loading image
Create a method which exchanges a given image and update the content size if needed
Add a routine do download the image
Now you can setup the UIScrollView and call the routine to download. Then when the download is done call the method to exchange the image and you are done.

Answer 3

Try to study GCD(GrandCentralDispatch) and work with your scenario's.
May be this will suits you.
-(void)loadthscroll:(NSMutableArray *)idarray:(NSMutableArray *)imgarray
{
scrollview_intheater= [[UIScrollView alloc] initWithFrame:CGRectMake(0, btn_thhead.frame.size.height,view_banner.frame.size.width, view_intheater.frame.size.height-btn_thhead.frame.size.height)];
[view_intheater addSubview:scrollview_intheater];
[scrollview_thcsoon removeFromSuperview];
adj=5;
currentx=5;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
//Here, do your iteration part like parsing URL from array and hitting the service which is background thread.
for(int i=0;i<[imgarray count];i++)
{
btn_theater_ct = [UIButton buttonWithType:UIButtonTypeCustom];
btn_theater_ct.frame=CGRectMake(currentx, 5, 95, 120);
[btn_theater_ct addTarget:self action:#selector(theaterAction:) forControlEvents:UIControlEventTouchDown];
[scrollview_intheater addSubview:btn_theater_ct];
currentx +=btn_theater_ct.frame.size.width+adj;
[scrollview_intheater setContentSize:CGSizeMake(currentx,0)];
NSLog(#"add th scroll--%d----%d",[imgarray count],i);
addr = [imgarray objectAtIndex:i];
addr = [addr stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding];
//NSLog(#"addr-------%#",addr);
data_theater = [NSData dataWithContentsOfURL:[NSURL URLWithString:addr ] ];
UIImage *receivedImage = [UIImage imageWithData:data_theater];
}
dispatch_async(dispatch_get_main_queue(), ^{
//Here, do your UI work like set the background image which is include in main thread
if([receivedImage isKindOfClass:[UIImage class]])
{
[btn_theater_ct setBackgroundImage: receivedImage];
btn_theater_ct.tag=i;
}
});
});
}