iOS Thread calling

Question

From Main UIViewController I call

  if (required) [dataDB function];
  next command;
  ....
  ....

in the Database UIViewController

- (void) Function {
  Display Alert Message for Processing;
  performs steps  (takes some time)
  ....
  ....
  Close Alert Message
}

Although one should NOT block code

I need the [dataDB Function] to complete before next command is called;

Yet I need the Alert to start showing before perform steps starts.

Currently Alert appears after [dataDB Function] completes and closes almost immediately.

Please help.

Answer 1

try this code

if (required)
    {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            [dataDB function];
            dispatch_async(dispatch_get_main_queue(), ^{
                next command;
            });
        });
    }

it will create async task of [dataDB function];and after competition of it, it will perform task on main queue of next command;