ios - How to multithred correctly? UIAlertView is not displayed, only gray screen -

i have implemented texttospeech in project , want display alertview while text spoken. here calling methods texttospeech:

//-----before tts starts try display alertview cancelbutton   //[self performselectoronmainthread:@selector(alertwhiletts) withobject:nil waituntildone:yes]; //gray view , no alertview //[self performselector:@selector(alertwhiletts)];  //gray view , no alertview //[self alertwhiletts];  //gray view , no alertview  //this part here blocking, no gray screen,  //after tts ready, alertview displayed dispatch_async(dispatch_get_main_queue(), ^{         //update ui if have         [self alertwhiletts];     });   [[self view] setneedsdisplay]; [self synthesizeinbackground]; [queue waituntilalloperationsarefinished]; [self setisspeaking: false]; [[self view] setneedsdisplay];   

here synthesizeinbackground method(in method synthesize starts tts):

- (void) synthesizeinbackground {     queue = [[nsoperationqueue alloc] init];     operation = [[nsinvocationoperation alloc] initwithtarget:self      selector:@selector(synthesize) object:nil];      [queue addoperation: operation]; }   

while tts want display alertview cancel button. in case getting gray screen without alertview.

how can call alertwhiletts correctly, alertview gets displayed?

here content of alertwhiletts:

- (void) alertwhiletts { uialertview *inboxread = [[[uialertview alloc] initwithtitle:@"inbox tts..."                                                     message:nil                                                    delegate:self                                           cancelbuttontitle:@"abbrechen"                                           otherbuttontitles:nil] autorelease]; inboxread.tag = 997;  [inboxread show]; }   

update see solution, works:

[self performselectoronmainthread:@selector(alertwhiletts) withobject:nil waituntildone:yes];      dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_default, (unsigned long)null), ^(void) {         [[self view] setneedsdisplay];         [self synthesizeinbackground];         [queue waituntilalloperationsarefinished];         [self setisspeaking: false];         [[self view] setneedsdisplay];      });  

change alertwithttsto

uialertview *inboxread = [[[uialertview alloc] initwithtitle:@"inbox tts..."                                                     message:nil                                                    delegate:self                                           cancelbuttontitle:@"abbrechen"                                           otherbuttontitles:nil] autorelease]; inboxread.tag = 997;  [inboxread show]; 

also dont forget call function alertwhiletts main ui thread doing

 dispatch_async(dispatch_get_main_queue(), ^{         //update ui if have         [self alertwhiletts];     });