Calling method from another class - Winforms C#

Question

I am trying something like below and I am getting red lines under any formDesign commands such as messageBox, dataGridView etc.

I want to put the body of the methods in a seperate .cs page for neatness and call them from mainForm.cs

Is this the wrong way to call methods

mainForm.cs

namespace App{
      public partial class mainForm : Form{
             private void saveCSVbutton_Click(object sender, EventArgs e){
                className.method();
             }
      }
}

class.cs

namespace App{
      class className{
              private void method(){MessageBox.Show("No Record To Export", "Info");}
      }
}

Answer 1

If you want to separate different layers of an app, I suggest you use a design pattern like MVVM. This way you would have classes that does the functionality of the app and other classes work with database and so on.