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

Your synchronous request blocks the UI thread and that’s why activity indicator will not start. You should use NSURLConnection asynchronously for multiple reasons, and that’s one of them.

Instead of:

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

Do:

NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];
[conn start];
[conn release];

Then make returnData instance variable and implement NSURLConnectionDeletgate methods:

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    returnData = [[NSMutableData alloc] init];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [returnData appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSString *returnString = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];
    // do whatever you need with your string and stop activity indicator
    [returnData release];
}