Question

I used form user control(instead of form in C# winform).

In this user control, i have one combo box and one textbox.

When combo box is changed, for selected value(1 or 2 or 3),text of textbox start with 1 or 2 or 3 respectively.

User can add 6 digit number in textbox but should not able to delete or change 1 or 2 or 3.

how do i do?

Answer 1

See if this will work, it is handling the TextChanged Event to verify that the first Character is the value from the ComboBox selection.

public partial class UserControl1 : UserControl
{
    string mask;

    public UserControl1()
    {
        InitializeComponent();
        textBox1.MaxLength = 7;
        textBox1.TextChanged += new EventHandler(textBox1_TextChanged);
        textBox1.KeyPress += new KeyPressEventHandler(textBox1_KeyPress);

    }

    void textBox1_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (!char.IsNumber(e.KeyChar) && !( e.KeyChar == 0x8) && !(e.KeyChar == 0xd))
            e.Handled = true;

    }

    void textBox1_TextChanged(object sender, EventArgs e)
    {
        TextBox tb = (TextBox)sender;

        char[] temp = tb.Text.ToCharArray(); //Code to catch any cut and Paste non numeric characters
        foreach (var item in temp)
        {
            if (!(char.IsNumber(item)))
            {
                tb.Text = "";
                break;
            }
        }

        if (tb.TextLength == 0)
        {
            tb.Text = mask[0].ToString();
            tb.SelectionStart = tb.Text.Length;

        }
        else
        {
            if (tb.Text[0] != mask[0])
            {
                tb.Text = mask[0] + tb.Text;
                tb.SelectionStart = tb.Text.Length;
            }
        }
    }

    private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        mask = ((ComboBox)sender).SelectedValue.ToString();
        textBox1.Text = mask;
    }

}