Xamarin iOS PushViewController null reference exception

Question

I'm new to Xamarin iOS developement and am having an issue that I can't figure out. When the following line of code runs, it throws a null reference exception and I can't figure out why.

this.NavigationController.PushViewController(location, true);

Here is my whole block of code.

partial void BtnLogin_TouchUpInside(UIButton sender)
    {
        if (txtPassword.Text != "" && txtUsername.Text != "")
        {
            //send UN & PD to webservice for validation.
            xxx.xxx.xxx.Services s = new xxx.xxx.xxx.Services();
            bool result = s.validateLogin(txtUsername.Text, txtPassword.Text);
            if (result)
            {
                try
                {
                    LocationViewController location = this.Storyboard.InstantiateViewController("LocationViewController") as LocationViewController;

                    if (location != null)
                        this.NavigationController.PushViewController(location, true);
                }
                catch (Exception ex)
                {
                    LoginFail("Error", ex.Message);
                }
            }
            else
            {
                LoginFail("Login", "Invalid username or password.");
            }
        }
        else
        {
            LoginFail("Login", "You must enter both your username and password.");
        }
    }

And my Storyboard

Answer 1

Because your login viewController is not in the NavigationController, So When you use this.NavigationController , it will throw null reference exception.

To solve this problem, two ways here:

• Put login ViewVontroller into NavigationController, make NavigationController(with the rootviewController of login page) become the initial Controller of storyboard.

• change this code this.NavigationController.PushViewController(location, true);

  To this.PresentViewController(location, true, null);