App crashed when trying to change UITextView.text - objective-c

Question

My app crashed when i trying to change UITextView text.
Here is the code: (header file):
//
#import <UIKit/UIKit.h>
#interface DetailViewController : UIViewController {
IBOutlet UIImageView *appImage;
IBOutlet UILabel *appName;
IBOutlet UILabel *appDeveloper;
IBOutlet UILabel *appVersion;
UIActivityIndicatorView *loading;
IBOutlet UITextView *appAbout;
NSString *selectedApp;
}
#property (nonatomic, retain) NSString *selectedApp;
#property (nonatomic, retain) IBOutlet UIImageView *appImage;
#property (nonatomic, retain) IBOutlet UILabel *appName;
#property (nonatomic, retain) IBOutlet UILabel *appDeveloper;
#property (nonatomic, retain) IBOutlet UILabel *appVersion;
#property (nonatomic, retain) UIActivityIndicatorView *loading;
#property (nonatomic, retain) UITextView *appAbout;
#end
implementation file:
- (void)loadData {
NSString *trimmedString = [selectedApp stringByReplacingOccurrencesOfString:#" " withString:#"%20"];
self.navigationItem.title = #"Info";
NSLog(#"%#", trimmedString);
NSString *website = [NSString stringWithFormat:#"http://shaymargolisapps.x10.mx/send.php?mission=GetNameOfApps&aname=%#", trimmedString];
NSData *dataURL = [NSData dataWithContentsOfURL:[NSURL URLWithString:website]];
NSString *strResult = [[[NSString alloc] initWithData:dataURL encoding:NSUTF8StringEncoding]autorelease];
appName.text = strResult;
NSString *website1 = [NSString stringWithFormat:#"http://shaymargolisapps.x10.mx/send.php?mission=GetDeveloperOfApp&aname=%#", trimmedString];
NSData *dataURL1 = [NSData dataWithContentsOfURL:[NSURL URLWithString:website1]];
NSString *strResult1 = [[[NSString alloc] initWithData:dataURL1 encoding:NSUTF8StringEncoding]autorelease];
appDeveloper.text = strResult1;
NSString *website2 = [NSString stringWithFormat:#"http://shaymargolisapps.x10.mx/send.php?mission=GetVersionOfApp&aname=%#", trimmedString];
NSData *dataURL2 = [NSData dataWithContentsOfURL:[NSURL URLWithString:website2]];
NSString *strResult2 = [[[NSString alloc] initWithData:dataURL2 encoding:NSUTF8StringEncoding]autorelease];
appVersion.text = strResult2;
NSString *website3 = [NSString stringWithFormat:#"http://shaymargolisapps.x10.mx/send.php?mission=GetInfoOfApp&aname=%#", trimmedString];
NSData *dataURL3 = [NSData dataWithContentsOfURL:[NSURL URLWithString:website3]];
NSString *strResult3 = [[[NSString alloc] initWithData:dataURL3 encoding:NSUTF8StringEncoding]autorelease];
NSLog(#"%#", strResult3);
**appAbout.text = strResult3;**
NSString *website4 = [NSString stringWithFormat:#"http://shaymargolisapps.x10.mx/send.php?mission=GetImageOfApp&aname=%#", trimmedString];
NSData *dataURL4 = [NSData dataWithContentsOfURL:[NSURL URLWithString:website4]];
NSString *strResult4 = [[[NSString alloc] initWithData:dataURL4 encoding:NSUTF8StringEncoding]autorelease];
NSData* imageData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:strResult4]];
UIImage* image = [[UIImage alloc] initWithData:imageData];
[appImage setImage:image];
[image release];
[imageData release];
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
[loading stopAnimating];
[loading setHidden:YES];
[appName setHidden:NO];
[appDeveloper setHidden:NO];
[appVersion setHidden:NO];
[appImage setHidden:NO];
[appAbout setHidden:NO];
}
My app crashed on appAbout.text = strResult3; line. What am I doing wrong?
loadData is called with [self performSelectorInBackground:#selector(loadData) withObject:nil]; from viewDidLoad
(Xcode 4.4 DP2, iPhone Simulator 5.1, base SDK 4.3)

Answer 1

You must not change UI* objects from a background thread. That has to be done from the main thread.
You could use gcd to perform the changes on the main thread. Something like this:
/* ... */
NSString *strResult4 = [[[NSString alloc] initWithData:dataURL4 encoding:NSUTF8StringEncoding]autorelease];
NSData* imageData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:strResult4]];
UIImage* image = [[UIImage alloc] initWithData:imageData];
dispatch_async(dispatch_get_main_queue(), ^{
self.navigationItem.title = #"Info";
appName.text = strResult;
appDeveloper.text = strResult1;
appVersion.text = strResult2;
appAbout.text = strResult3;
[appImage setImage:image];
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
[loading stopAnimating];
[loading setHidden:YES];
[appName setHidden:NO];
[appDeveloper setHidden:NO];
[appVersion setHidden:NO];
[appImage setHidden:NO];
[appAbout setHidden:NO];
});
[image release];
[imageData release];