Question

I’m trying to make a simple program with GUI in c# but unfortunately I have some difficulties. Now I’ll try to explain the basic structure of my program. I have 3 classes for three different groups of people(University Professors, University Students and people who don’t work or study either). I have some methods for reading information from a file(professor’s title, name, university name, student’s faculty number, etc.). I read the file line by line and save the information in an object of type one of the 3 classes. After that I put that object in a List. So here comes my problem. I want to read every object from the list and take its name and put in on a dynamically created labels on other windows form. Here it is a little part of my code:

private void button1_Click(object sender, EventArgs e)
{
        ForeignPeople fPeople = new ForeignPeople();
        UniversityProfessors uProf = new UniversityProfessors();
        UniversityStudents uStudents = new UniversityStudents();
        if (radioButton1.Checked == true)
        {
            objList1 = loadList();
            Form2 f2 = new Form2();
            for (int i = 0; i < objList1.Count; i++)
            {
                if (objList1[i] is UniversityStudents)
                {
                    uStudents = (UniversityStudents)objList1[i];
                    tableLayoutPanel1.GrowStyle = TableLayoutPanelGrowStyle.AddRows;
                    Label et_tag = new Label();
                    et_tag.Name = "label" + i.ToString();
                    et_tag.Text = uStudents.getFirstName().ToString() + " " + uStudents.getLastName().ToString();
                    et_tag.AutoSize = true;
                    f2.tableLayoutPanel1.Controls.Add(et_tag, 0, i);
                    Label op = new Label();
                    op.AutoSize = true;
                    op.Text = "description";
                    f2.tableLayoutPanel1.Controls.Add(op, 1, i);
                }
                else if (objList1[i] is UniversityProfessors)
                {
                    uProf = (UniversityProfessors)objList1[i];
                    tableLayoutPanel1.GrowStyle = TableLayoutPanelGrowStyle.AddRows;
                    Label et_tag = new Label();
                    Label label = new Label();
                    et_tag.Name = "label" + i.ToString();
                    et_tag.Text = uProf.getFirstName().ToString() + " " + uProf.getLastName().ToString();
                    et_tag.AutoSize = true;
                    f2.tableLayoutPanel1.Controls.Add(et_tag, 0, i);
                    Label op = new Label();
                    op.AutoSize = true;
                    op.Text = "description";
                    f2.tableLayoutPanel1.Controls.Add(op, 1, i);
                }
                else if (objList1[i] is ForeignPeople)
                {
                    fPeople = (ForeignPeople)objList1[i];
                    String name, Name;
                    tableLayoutPanel1.GrowStyle = TableLayoutPanelGrowStyle.AddRows;
                    Label et_tag = new Label();
                    et_tag.Name = "label" + i.ToString();
                    et_tag.Text = fPeople.getFirstName().ToString() + " " + fPeople.getLastName().ToString();;
                    et_tag.AutoSize = true;
                    f2.tableLayoutPanel1.Controls.Add(et_tag, 0, i);
                    Label op = new Label();
                    op.AutoSize = true;
                    op.Text = "description";
                    f2.tableLayoutPanel1.Controls.Add(op, 1, i);
                }

            }
            f2.FormClosed += new FormClosedEventHandler(childFormClosed);
            f2.Show();
            this.Hide();
}

But if I have two or more lines which belongs to one Object(for example I have two or more students, or two or more professors in the file) the text of all the labels becomes with the name of the last read object. I know that the problem is in the List or in the cast which I make but I can’t figure out another way of doing what I want. I’ll be extremely grateful if someone can help.

Answer 1

In addition to the change that phoog mentioned in the comments, I would also move the instantiation of your “people” objects down into the section for each within the loop. That way you can be sure that the old one is being properly destroyed. I would also add a check to make sure that the cast worked.

private void button1_Click(object sender, EventArgs e)
{
    if (radioButton1.Checked == true)
    {
        objList1 = loadList();
        Form2 f2 = new Form2();

        for (int i = 0; i < objList1.Count; i++)
        {
            if (objList1[i] is UniversityStudents)
            {
                UniversityStudents uStudents = (UniversityStudents)objList1[i];

                if (uStudents != null)
                {
                    // do stuff
                }
                else
                {
                    // do something sensible with the error here
                }
            }
            // if clauses for the other "people" objects
            // ...
        }
        f2.FormClosed += new FormClosedEventHandler(childFormClosed);
        f2.Show();
        this.Hide();
    }
}