Show activity indicator animation when button pressed

Question

I have a button called "Sync". When tapped / pressed it sends data to a webserver and retrieves the answer by the server (what takes a while and freezes the gui / button) so how do I add a "Please wait" and activity indicator until the data / answer from the server arrives and the text / indicator is deleted and replaced by the answer from the server?

This code freezes my app:

- (IBAction) syncButtonTapped
{

[syncButton setEnabled:NO];
//resultText.text= @"Bitte warten ...";
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *docDir = [paths objectAtIndex: 0];
NSString *docFile = [docDir stringByAppendingPathComponent: @"deck.txt"];
NSString *post = [NSString stringWithContentsOfFile:docFile encoding:NSUTF8StringEncoding error:nil];


NSString *post2 = [post stringByReplacingOccurrencesOfString:@"\n" withString:@","];
NSString *post3 = [post2 stringByReplacingOccurrencesOfString:@"\r" withString:@""];
NSString *post4 = [NSString stringWithFormat:@"{\"results\":[%@]}",post3];
NSString *urlString = [NSString stringWithFormat:@"http://storecheck.cortona.de/fetchresults.php?results=%@",[post4 stringByAddingPercentEscapesUsingEncoding: NSASCIIStringEncoding]];
NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease]; 
[request setURL:[NSURL URLWithString:urlString]]; 
[request setHTTPMethod:@"GET"];
 NSString *data4 = @"";
[data4 writeToFile: docFile atomically: NO encoding: NSUTF8StringEncoding error:nil];
//send request & get response

NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
NSString *returnString = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];
}

i am working on a Mac Mini with iOS 10.6.7

Answer 1

Adding an activity indicator in UIAleartView will help. Checkout this...

UIAlertView *waitAlert = [[[UIAlertView alloc] initWithTitle:@"Please Wait...." message:nil delegate:self cancelButtonTitle:nil otherButtonTitles: nil] autorelease];

[waitAlert show];

UIActivityIndicatorView *indicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];

// Adjust the indicator so it is up a few pixels from the bottom of the alert
indicator.center = CGPointMake(waitAlert.bounds.size.width / 2, waitAlert.bounds.size.height - 50);
[indicator startAnimating];
[waitAlert addSubview:indicator];
[indicator release];

EDIT: Probably the reason why your application is getting blocked is this method

sendSynchronousRequest:(NSURLRequest *)request

Following is the description of the method.

A synchronous load is built on top of the asynchronous loading code made available by the class. The calling thread is blocked while the asynchronous loading system performs the URL load on a thread spawned specifically for this load request. No special threading or run loop configuration is necessary in the calling thread in order to perform a synchronous load.

If you don't want you application to block then call this from other thread. Read following too.

Important: Because this call can potentially take several minutes to fail (particularly when using a cellular network in iOS), you should never call this function from the main thread of a GUI application.

Please refer to Class reference of NSURLConnection. Both of above blocks are taken from that.

http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSURLConnection_Class/Reference/Reference.html