UIAlertController* alert = [UIAlertController alertControllerWithTitle:@"My Alert"
                                  message:@"This is an alert."
                              preferredStyle:UIAlertControllerStyleAlert];

  UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault
                             handler:^(UIAlertAction * action) {
                               NSLog(@"你好你好");
                             }];

  UIAlertAction* defaultAction2 = [UIAlertAction actionWithTitle:@"OK2" style:UIAlertActionStyleDefault
                             handler:^(UIAlertAction * action) {
                               NSLog(@"你好你好");
                             }];

  [alert addAction:defaultAction];
  [alert addAction:defaultAction2];
  [self presentViewController:alert animated:YES completion:nil];

  [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
    textField.placeholder = @"输入用户名";
  }];