How to turn an asynchronous method into a synchronous method

Question

I'm calling one method from another method.The method exits in the middile. After completing some tasks, it will run the remaining method.

-(void)stateMethod{
    [self.pickerView selectRow:0 inComponent:0 animated:YES];
    lblTitle.text=@"State";
    self.stateTF.text=@"";
    self.stateTF.inputView=_pickerView;
    [self.stateTF setInputAccessoryView:toolBar];
    NSString * method=@"***************************?countryID=";
    NSString *urlString=[NSString stringWithFormat:@"%@%@%@",MAIN_URL,method,_countryId];
    NSURL *url_ac=[[NSURL alloc]initWithString:urlString];
    NSMutableURLRequest *request_ac=[[NSMutableURLRequest alloc]initWithURL:url_ac];
    [request_ac setValue:loginUser.acessTokenStr forHTTPHeaderField:@"access_token"];

   [NSURLConnection sendAsynchronousRequest:request_ac queue:[NSOperationQueue currentQueue] completionHandler:
 ^(NSURLResponse ac_response, NSData acData, NSError *connectionError) {
     if (connectionError)
     {
         NSLog(@"ERROR CONNECTING DATA FROM SERVER: %@", connectionError.localizedDescription);
     }
    else {            
    dispatch_async(dispatch_get_main_queue(), ^{
             NSString *responseString = [[NSString alloc] initWithData:acData encoding:NSUTF8StringEncoding];
             [self parseStateListResult:acData];
         });
     }
 }];  
}

I want the response when i'm calling the state method. Based on state method response,i'm executing one task after calling [self statemethod]. That task need 'state methodresponce. That task is executing before getting the data from state method. The method exits afterNSURLConnection` line. I want to run the method asynchronously. Please help me.

Answer 1

I'm calling one method from another method.The method exits in the middile. After completing some tasks, it will run the remaining method.

It doesn't exit in the middle... the part after the sendAsynchronousRequest call is a completion handler. It's a separate block of code that you're passing into the request to run at a later time. Think of it as a parameter to the method, not part of the code of stateMethod.

With that in mind, you can see that stateMethod really does run to the end, because the last line of code in the method is the sendAsyncronousRequest call.

Based on state method response, I'm executing one task after calling [self statemethod]. That task need state method responce. That task is executing before getting the data from state method. The method exits after NSURLConnection line. I want to run the method asynchronously.

Since you haven't given the name of the method that needs the response, let's just call it foo. Your problem is that the request is asynchronous, so foo gets called before the response is available. One way to handle that would be to put the call to foo inside the request's completion block, but you might not want to do that directly because stateMethod might be called from several places, only one of which subsequently calls foo. Instead, you might change stateMethod so that the caller can specify a completion block:

-(void)stateMethodWithCompletion:(nullable void (^)(NSURLResponse* response))stateCompletion {
    [self.pickerView selectRow:0 inComponent:0 animated:YES];
    lblTitle.text=@"State";
    self.stateTF.text=@"";
    self.stateTF.inputView=_pickerView;
    [self.stateTF setInputAccessoryView:toolBar];
    NSString * method=@"***************************?countryID=";
    NSString *urlString=[NSString stringWithFormat:@"%@%@%@",MAIN_URL,method,_countryId];
    NSURL *url_ac=[[NSURL alloc]initWithString:urlString];
    NSMutableURLRequest *request_ac=[[NSMutableURLRequest alloc]initWithURL:url_ac];
    [request_ac setValue:loginUser.acessTokenStr forHTTPHeaderField:@"access_token"];

    [NSURLConnection sendAsynchronousRequest:request_ac queue:[NSOperationQueue currentQueue] completionHandler:
        ^(NSURLResponse ac_response, NSData acData, NSError *connectionError) {
        if (connectionError) {
             NSLog(@"ERROR CONNECTING DATA FROM SERVER: %@", connectionError.localizedDescription);
        }
        else {
            if (stateCompletion != nil) {
                stateCompletion(acResponse);
            }
            dispatch_async(dispatch_get_main_queue(), ^{
                     NSString *responseString = [[NSString alloc] initWithData:acData encoding:NSUTF8StringEncoding];
                     [self parseStateListResult:acData];
                 });
        }
    }];  
}

That replaces the old stateMethod, but if you want to have a version that doesn't have the extra parameter you can always do that too:

-(void)stateMethod {
     [self stateMethodWithCompletion:nil];
}