Question

In my C# (3.5) solution, i have 2 projects- a Class Library and WinForm project.

All business logic are in class library. while adding/updating data from WinForm, if Class Library finds any error, it will raise error and set focus to associate control in WinForm.

Is it possible?

Thanks,
SKPaul.

Answer 1

All UI logic should remain in your WinForm project. You will have to pass your control to class library to set focus from the library which is mostly a bad design. Instead:

namespace ClassLibrary
{
    public class Utility
    {
        public static string ReadData()
        {
            return "abc";
        }
    }
}

namespace Win_App
{
    public partial class Form1 : Form
    {
       private void button2_Click(object sender, EventArgs e)
       {
            if (ClassLibrary.Utility.ReadData() == null)
            {
                MessageBox.Show("error, redo");
                button2.Focus(); //you should handle this here.
                return;
            }
        }
    }
}

The basic idea here is to signal an appropriate return value in case of an error. For instance a null value for an object, or a false for a bool value. You should check that in UI project, and handle it there. In your case setting focus hence should be from WinForm project.