objective c - OSX application freezes when try to set the value of TextView? -

i new objective-c.

first please see code:

here property:

@property (atomic) iboutlet nstextview *txtresponse; 

and here action:

- (ibaction)sendreq:(id)sender {     @synchronized(self)     {         request *req = [[request alloc] init];          voidcallback callback = ^(nsurlresponse *resp,  nsdata *data, nserror *error) {             nsstring *val = [[nsstring alloc] initwithdata:data encoding:nsutf8stringencoding];              [self.txtresponse setstring:val];             //nslog(val);         };          [req seturl:[[nsurl alloc] initwithstring:@"http://foo.bar"]];          [req setcallback:callback];          [req send];     } } 

the ui freezes when try use [self.txtresponse setstring:val];
tried code without @synchronized(self)
problem?
in advance!

3rd day working objective-c , found answer :)

i used performselectoronmainthread , solved problem

- (ibaction)sendreq:(id)sender {      request *req = [[request alloc] init];      voidcallback callback = ^(nsurlresponse *resp,  nsdata *data, nserror *error) {         nsstring *val = [[nsstring alloc] initwithdata:data encoding:nsutf8stringencoding];          [self performselectoronmainthread:@selector(setresponsevalue:) withobject:val waituntildone:no];     };      [req seturl:[[nsurl alloc] initwithstring:@"http://programming.com"]];      [req setcallback:callback];      [req send]; }  - (void)setresponsevalue:(nsstring *)resp {     [self.txtresponse setstring:resp];     //nslog(resp); }