Issue with editing data within a list box using multiple forms

Question

In my program I allow the user to select a student record from the list box, when they hit the edit button a new form opens. This form displays the id and mark of the student they have selected. I am required to let the user edit that mark and update the list box. I am having trouble letting the user edit, and would appreciate any advice on this. (I am having trouble figuring out what to do when I have the user's data inside the edit form)

I'm not allowed to use LINQ, so a solution or advice on how to do it without it would be greatly appreciated.

Main form:

private void btnEditMark_Click(object sender, EventArgs e) {
    string[] s_rec_arr;

    if (lstMarks.SelectedIndex == -1) {
        MessageBox.Show("please select a student");
    } else {
        ModuleData.s_rec = lstMarks.SelectedItem.ToString();
        s_rec_arr = ModuleData.s_rec.Split(':');
        ModuleData.s_id = s_rec_arr[0];
        ModuleData.s_mark = s_rec_arr[1];
        editMark myEditRecordForm = new editMark();
        this.Hide();
        myEditRecordForm.ShowDialog();
    }
}

Edit form:

public partial class editMark : Form {
    public editMark() {
        InitializeComponent();
        StartPosition = FormStartPosition.CenterScreen;
        txtStudentID.Focus();
    }

    private void btnSubmit_Click(object sender, EventArgs e) {
    }

    private void btnClose_Click(object sender, EventArgs e) {
        this.Hide();
        Form1 myForm = new Form1();
        myForm.ShowDialog();
    }

    private void editMark_Load(object sender, EventArgs e) {
        txtStudentID.Text = ModuleData.s_id;
        txtMark.Text = ModuleData.s_mark;
    }
}

Answer 1

You can add any type of object to a list box, not just strings. Create a student class and add Student objects to the listbox. Or maybe you prefer to use your ModuleData class. But in any case, you don't need to use s_rec with a colon-separated string.

public class Student
{
    public string Id { get; set; }
    public string Mark { get; set; }

    // Required to make to have the list box display useful information about students.
    public override string ToString()
    {
        return $"Id = {Id}, Mark = {Mark}";
    }
}

Now add a parameter to the edit form's constructor to be able to pass the student

private Student _student;

public editMark(Student student)
{
    InitializeComponent();

    // Remember the student
    _student = student;

    StartPosition = FormStartPosition.CenterScreen;

    txtStudentID.Text = student.Id;
    txtMark.Text = student.Mark;
    txtStudentID.Focus();
}

In the editform, if you do Form1 myForm = new Form1();, this will create a new instance of Form1 instead of of using the existing hidden one.

Remember that a class is a reference type, therefore it is not necessary to pass the student back to the first form, because this one also has a reference to the same student. Only update its properties

private void btnClose_Click(object sender, EventArgs e)
{
    _student.Id = txtStudentID.Text; // Only id the Id is editable.
    _student.Mark = txtMark.Text;

    Close();
}

In the main form

private void BtnEditMark_Click(object sender, EventArgs e)
{
    if (lstMarks.SelectedIndex == -1) {
        MessageBox.Show("please select a student");
    } else {
        var student = (Student)lstMarks.SelectedItem;

        // Pass the student as to the edit form
        var myEditRecordForm = new editMark(student);
        Hide();
        myEditRecordForm.ShowDialog(); // The code pauses here until the edit form is closed.
        Show(); // Doing this here prevents you from having the edit form knowing about Form1.

        // To display the changes.
        lstMarks.Items[lstMarks.SelectedIndex] = student;
    }
}