C# - Disabling Keyboard Input into a Textbox

Question

I am trying to disable all keystrokes entered into a text box except the following:

0 1 2 3 4 5 6 7 8 9 . (so all keys except the numbers and the '.' should be disabled)

Right now I have the following code but it only checks to see if a letter was entered as the first value (not to mention its really sloppy):

    private void yDisplacementTextBox_TextChanged(object sender, EventArgs e)
    {
         if (yDisplacementTextBox.Text.ToUpper() == "A" || yDisplacementTextBox.Text.ToUpper() == "B" || yDisplacementTextBox.Text.ToUpper() == "C" ||
             yDisplacementTextBox.Text.ToUpper() == "D" || yDisplacementTextBox.Text.ToUpper() == "E" || yDisplacementTextBox.Text.ToUpper() == "F" || 
             yDisplacementTextBox.Text.ToUpper() == "G" || yDisplacementTextBox.Text.ToUpper() == "H" || yDisplacementTextBox.Text.ToUpper() == "I" ||
             yDisplacementTextBox.Text.ToUpper() == "J" || yDisplacementTextBox.Text.ToUpper() == "K" || yDisplacementTextBox.Text.ToUpper() == "L" ||
             yDisplacementTextBox.Text.ToUpper() == "M" || yDisplacementTextBox.Text.ToUpper() == "N" || yDisplacementTextBox.Text.ToUpper() == "O" ||
             yDisplacementTextBox.Text.ToUpper() == "P" || yDisplacementTextBox.Text.ToUpper() == "Q" || yDisplacementTextBox.Text.ToUpper() == "R" ||
             yDisplacementTextBox.Text.ToUpper() == "S" || yDisplacementTextBox.Text.ToUpper() == "T" || yDisplacementTextBox.Text.ToUpper() == "U" ||
             yDisplacementTextBox.Text.ToUpper() == "V" || yDisplacementTextBox.Text.ToUpper() == "W" || yDisplacementTextBox.Text.ToUpper() == "X" ||
             yDisplacementTextBox.Text.ToUpper() == "Y" || yDisplacementTextBox.Text.ToUpper() == "Z")
        {
            MessageBox.Show("Please enter a numeric value for the Y Displacement.", "Y Displacement: Numbers Only Error",
                       MessageBoxButtons.OK, MessageBoxIcon.Warning);
        }
    }

Is there anyway to have it so when pressed, all of the keys on the keyboard (except the numbers and the period button) do not register (or disables) the actual value of the key and inputs nothing?

as a first suggestion, your logic would be much simpler to look for the letters you DO want to allow, and ignoring (or prompting) anything that isn't 0-9 or .. — Tim Coker
– Tim Coker, Commented Jul 18, 2011 at 23:29
Is this winforms or wpf? You should remove the input tag, and add one of those tags. — Merlyn Morgan-Graham
– Merlyn Morgan-Graham, Commented Jul 18, 2011 at 23:32

Jalal Said · Accepted Answer · 2011-07-19 00:52:15Z

6

Use textBox1.KeyPress += textBox1_KeyPress

This code only allowing numbers and . and the backspace.

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if ((e.KeyChar > (char)Keys.D9 || e.KeyChar < (char)Keys.D0) && e.KeyChar != (char)Keys.Back && e.KeyChar != '.')
    { 
        e.Handled = true; 
    }
    //Edit: Alternative
    if (!char.IsDigit(e.KeyChar) && e.KeyChar != (char)Keys.Back && e.KeyChar != '.')
    {
        e.Handled = true;
    }
}

edited Jul 19, 2011 at 0:52

answered Jul 18, 2011 at 23:29

Jalal Said

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3 Comments

Rubens Farias Over a year ago

Char.IsNumber() can be useful here

Jalal Said Over a year ago

@Rubens: you are right, I add to answer as alternative, thanks.

Alirezaarabi Over a year ago

this method allows Enter

Dan Walker · Accepted Answer · 2011-07-18 23:28:59Z

1

There are two ways you could try to approach this:

Wait for the user to finish entering the data, then use double.TryParse() to make sure it's a valid number.
Use the KeyPress event of the TextBox to validate the data as each key is pressed.

answered Jul 18, 2011 at 23:28

Dan Walker

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Comments

Rubens Farias · Accepted Answer · 2011-07-18 23:29:40Z

0

Take a look here: Simple Numeric TextBox

EDIT: As other answers explains what to do dealing with OnKeyPress/OnKeyDown events, this article demonstrates how to deal with other scenarios, as pasting text, so I'll keep this answer.

answered Jul 18, 2011 at 23:29

Rubens Farias

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Comments

ChrisWue · Accepted Answer · 2011-07-18 23:30:41Z

0

You should hook into the KeyDown and KeyPress event to prevent the input of unwanted characters. There is a sample on MSDN

answered Jul 18, 2011 at 23:30

ChrisWue

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Comments

Tory Netherton · Accepted Answer · 2011-07-18 23:35:21Z

0

Many third party control libraries also have this kind of functionality built in if you ever find yourself using one of them.

answered Jul 18, 2011 at 23:35

Tory Netherton

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Comments

Marino Šimić · Accepted Answer · 2011-07-18 23:48:17Z

0

It is better practice to allow typing anything but give notification through an error provider about the failing validation (Validating event and double.TryParse()).

But if you insist, be sure to replace the '.' with the decimal separator of the system. If you are not assuming all values to be English you can easily get into a cannot-enter-a-decimal-value problem.

For instance, I am in Croatia and here we have to type a comma (,). In some islamic country I fail to remember the decimal separator is a hash (#).

So beware of localization issues.

answered Jul 18, 2011 at 23:48

Marino Šimić

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Comments

Loren Shaw · Accepted Answer · 2012-11-29 19:29:54Z

0

The below code will suppress all but number, the backspace, and the decimal. It also only allows a single decimal for numeric entry.

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if ((e.KeyChar > (char)Keys.D9 || e.KeyChar < (char)Keys.D0) && e.KeyChar != (char)Keys.Back && e.KeyChar != '.')
    { 
        e.Handled = true;
        return; 
    }
    if(e.KeyChar == '.' && textBox1.Text.Contains('.'))
    {
        e.Handled = true;
    }
}

answered Nov 29, 2012 at 19:29

Loren Shaw

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Comments

Syamilsynz · Accepted Answer · 2013-12-02 03:07:28Z

0

This also can be used

if (!Char.IsDigit(e.KeyChar) && e.KeyChar != '\b' && e.KeyChar != '.'){
            e.Handled = true;}

answered Dec 2, 2013 at 3:07

Syamilsynz

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TNM · Accepted Answer · 2018-07-13 11:00:59Z

0

Shortest fix to make text/cmb box read-only, attach following to respective keypress event :

private void cmbDisable_KeyPress(object sender, KeyPressEventArgs e) { e.KeyChar = (char)(0); }

answered Jul 13, 2018 at 11:00

TNM

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