NSThread to stop process - iphone

Question

I am using a navigation base application. When I go to next view or back to the previous view, the thread does not stop. Can someone give me a solution for stopping the thread when switching between views? When I switch to next or previous, the application crashes. I use thread like this for downloading the image
- (void)viewWillAppear:(BOOL)animated {
AppDeleget= [[UIApplication sharedApplication] delegate];
ProcessView *Process=[[ProcessView alloc] init];
[Process SearchProperty:AppDeleget.PropertyURL page:AppDeleget.Page];
[Process release];
for(NSDictionary *status in AppDeleget.statuses)
{
NSMutableString *pic_string = [[NSMutableString alloc] initWithFormat:#"%#",[status objectForKey:#"picture"]];
if([pic_string isEqualToString:#""])
{
[ListPhotos addObject:#"NA"];
}
else
{
NSString *str= [[[status objectForKey:#"picture"] valueForKey:#"url"] objectAtIndex:0];
[ListPhotos addObject:str];
}
}
[NSThread detachNewThreadSelector:#selector(LoadImage) toTarget:self withObject:nil];
[AppDeleget.MyProgressView stopAnimating];
[AppDeleget.Progress removeFromSuperview];
[super viewWillAppear:animated];
}
-(void)LoadImage
{
for(int x=0;x<[ListPhotos count];x++)
{
NSData *imageData =[ListPhotos objectAtIndex:x];
id path = imageData;
NSURL *url = [NSURL URLWithString:path];
NSLog(#"%#",url);
NSData *data = [NSData dataWithContentsOfURL:url];
UIImage *img = [[UIImage alloc] initWithData:data];
[self performSelectorOnMainThread:#selector(downloadDone:) withObject:img waitUntilDone:NO];
}
}
-(void)downloadDone:(UIImage*)img {
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:count inSection:0];
if(img == nil)
{
TableCell *cell = (TableCell *)[TableView cellForRowAtIndexPath:indexPath];
cell.myImageView.image=[UIImage imageNamed:#"No_image.png"];
++count;
[TableView reloadData];
}
else
{
TableCell *cell = (TableCell *)[TableView cellForRowAtIndexPath:indexPath];
cell.myImageView.image=img;
++count;
[TableView reloadData];
}
}

Answer 1

You can cancel a thread which is being executed using the instance method cancel
[yourThread cancel];
Or you can use exit
[yourThread exit];
which will terminate the thread

Answer 2

You have started the thread in viewWillAppear, hence it will get called when you switch between your view controllers. If you want to execute your thread only once, then try putting it in viewDidLoad.