User Input - Data Validation

Question

I'm accepting a string value from the user via a text box in a form. It is then used in a query against a database table and although it is a string, I require the only characters entered to be whole numbers.

I've tried various methods, such as the INT32 and TryParse functions. However, I run into issues when attempting an IF ELSE or TRY CATCH to prevent anything from executing until the input is 'acceptable'.

What is the easiest way to allow whole numbers only to be entered into the text box, or to identify anything but whole numbers and fail the execution?

Tim Schmelter · Accepted Answer · 2013-03-28 15:11:15Z

3

Yes, you can use int.TryParse:

string selectSql = "SELECT * FROM SomeTable WHERE ID = @ID";

int id;
if (!int.TryParse(txtID.Text, out id))
    MessageBox.Show("ID must be an integer.");
else
{
    using (var myCon = new SqlConnection(connectionString))
    using (var selectCommand = new SqlCommand(selectSql, myCon))
    {
        selectCommand.Parameters.AddWithValue("@ID", id);
        myCon.Open();
        using (var reader = selectCommand.ExecuteReader())
        {
            // do something with the records
        }
    }
}

You can also use a NumericUpDown control.

answered Mar 28, 2013 at 15:11

Tim Schmelter

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Comments

Michael Ross · Accepted Answer · 2013-03-28 15:09:09Z

1

Use a NumericUpDown control instead of a TextBox

answered Mar 28, 2013 at 15:09

Michael Ross

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1 Comment

William Over a year ago

The NumericUpDown allows other characters, such as ,.-

Arie · Accepted Answer · 2013-03-28 15:28:02Z

I know of 3 possible ways to do it:

Remove invalid characters in TextChanged event of your textbox:

private void txb_TextChanged(object sender, EventArgs e)
{
int selStart = txb.SelectionStart;

string result = txb.Text;

// remove all that aren't digits
result = Regex.Replace(result, @"[^0-9]", string.Empty);

txb.Text = result;

// move cursor
if (selStart > txb.Text.Length)
    txb.Select(txb.Text.Length, 0);
else txb.Select(selStart, 0);
}

Extend TextBox control and ignore all invalid keys that user presses

public class IntegerTextBox : TextBox
{
private Keys[] int_allowed = {
         Keys.D1,
         Keys.D2,
         Keys.D3,
         Keys.D4,
         Keys.D5,
         Keys.D6,
         Keys.D7,
         Keys.D8,
         Keys.D9,
         Keys.D0,
         Keys.NumPad0,
         Keys.NumPad1,
         Keys.NumPad2,
         Keys.NumPad3,
         Keys.NumPad4,
         Keys.NumPad5,
         Keys.NumPad6,
         Keys.NumPad7,
         Keys.NumPad8,
         Keys.NumPad9,
         Keys.Back,
         Keys.Delete,
         Keys.Tab,
         Keys.Enter,
         Keys.Up,
         Keys.Down,
         Keys.Left,
         Keys.Right
    };
 protected override void OnKeyDown(KeyEventArgs e)
        {
            base.OnKeyDown(e);
            if (e.Modifiers == Keys.Control) return;

            if (!int_allowed.Contains(e.KeyCode))
            {
                e.SuppressKeyPress = true;
            }
        }
    }
}

process KeyDown and/or KeyPress event and cancel it if somthing that isn't allowed was pressed

SkyterX · Accepted Answer · 2013-03-28 15:13:38Z

You can write your own class that inherits from TextBox:

    public class NumericTextBox : TextBox
{
    protected override void OnKeyPress(KeyPressEventArgs e)
    {
        base.OnKeyPress(e);

        var key = e.KeyChar + "";
        if (key == "\b")
            return;
        double number;
        string newText = Text.Remove(SelectionStart, SelectionLength).Insert(SelectionStart, key);
        if (newText.Length == 1 && key == "-")
            return;
        if (!double.TryParse(newText, NumberStyles.Float, CultureInfo.InvariantCulture, out number))
        {
            e.Handled = true;
        }
    }

    public double Value
    {
        get { return Text.Length == 0 ? 0 : double.Parse(Text, CultureInfo.InvariantCulture); }
    }
}

James · Accepted Answer · 2013-03-28 15:18:31Z

0

Just as another alternative you could use the textboxes TextChanged event.

int.TryParse the text everytime the value is changed, if it doesn't work just clear the textbox (or keep the last value that worked and revert to that on fail).

answered Mar 28, 2013 at 15:18

James

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