How do I make a TextBox accept numbers only.

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I am making a Calculator app. I want it's TextBox(where the numbers are entered) to accept numbers and a decimal point only. How do I do that? Can anyone help me? Thanx in advance.

Posted 15-May-14 3:43am

Anas Tasadduq

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[no name] 15-May-14 9:51am

Yes just about anyone can help you if you try something. There must be thousands of examples of this for you to look at. Have you done any research? Have you written any code?

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CHill60 · Accepted Answer · 2014-05-15T03:47:00

Solution 1

Timing! There is a very similar post here Validation for a text box with alphanumeric[^] which just came in!

Using the solution I just posted there you can try this

C#

private void textBox1_Validating(object sender, CancelEventArgs e)
{
    //Cancel the exit from the textBox if it is not all numeric
    e.Cancel = !Regex.IsMatch(textBox1.Text, @"^\d+$");
}

{Edit - Validating event not required here as only numeric allowed and that will be forced by the KeyPress event below

C#

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    //"handle" the key press if is not numeric or backspace
    //because it is handled here it won't appear in the textBox
    e.Handled = !(Char.IsDigit(e.KeyChar) || e.KeyChar == '\b' || e.KeyChar == '.');
}

Posted 15-May-14 3:47am

CHill60

Updated 15-May-14 4:18am

v2

Comments

Anas Tasadduq 15-May-14 9:57am

I'm a beginner, so may I know what is Regex, KeyChar and IsDigit? And what does e.Handled means? And why one method is "Validating" and one is "KeyPress"?

CHill60 15-May-14 10:16am

See comment from Nilesh Avhad.
e is the parameter set KeyPressEventArgs that is passed to this Event Handler whenever a key is pressed when textBox1 has focus. The Handled property can be set to true to indicate that no further action is required for this keystroke - i.e. it has already been "handled". If set to true then the keyboard character pressed will not appear in the text box.
The reason for the two events ... the KeyPress event is called every time a key is pressed when textBox1 has focus. By using this event to determine whether or not we want to ignore the key (i.e. it is not a number) then we tell the user at the very earliest opportunity that we are not going to accept that particular key as input.
However, if we want to validate the *entire* set of information they have entered into the textbox then we have to wait until they have finished typing, and leave the textbox. That is when the <cod>Validating event will fire.
I've also just realised that I posted both event handlers when really only the KeyPress handler is required (the other one came from an earlier post - sorry). I will amend my solution

Anas Tasadduq 15-May-14 13:03pm

Thanks a lot!

Emre Ataseven 15-May-14 11:06am

You need to read something before asking it imo.

Telstra 15-May-14 10:03am

Regex means Regular Expression. It is used for validation like in this example @"^\d+$" this expression is validating that user should enter number only.
KeyChar means the ASCII code of key which you pressed on keyboard.
IsDigit means is this a digit or character.

Anas Tasadduq 15-May-14 13:03pm

Thanx!

Member 13068046 21-Mar-17 21:43pm

I'm currently trying to get this to work in visual studio's 2015 but the code keeps giving me an error. Does anyone know why?

private void txt_P1In_KeyPress(object sender, KeyPressEventArgs e)
{
e.Handled = !(Char.IsDigit(e.KeyChar) || e.KeyChar == '\b' || e.KeyChar = '.');
}

CHill60 22-Mar-17 7:13am

That line should read e.Handled = !(Char.IsDigit(e.KeyChar) || e.KeyChar == '\b' || e.KeyChar == '.'); Note the == '.' NOT = '.'