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C# TextBox convert numbers

I have textbox that I managed to accept numbers only by KeyPress but I cannot make input numbers separated by commas.
private void inputAmount_KeyPress(object sender, KeyPressEventArgs e)
{
if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && (e.KeyChar != '.'))
{
e.Handled = true;
// this doesn't work
inputAmount.Text = string.Format("{0:#,##}", e.KeyChar);
}
}
What I'm looking for is: when user starts typing numbers in text box it separate thousands by commas while user typing.
Any idea?
Update
I've added second function TextChanged as following and removed inputAmount.Text = string.Format("{0:#,##}", e.KeyChar); line from code above.
It does add thousands separators to my input but it keeps jumping to beginning of the numbers
private void inputAmount_TextChanged(object sender, EventArgs e)
{
inputAmount.Text = string.Format("{0:#,##0}", double.Parse(inputAmount.Text));
}

Solved
Here is my final code that solved the issue
// Only accept numbers
private void inputAmount_KeyPress(object sender, KeyPressEventArgs e)
{
if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && (e.KeyChar != '.'))
{
e.Handled = true;
}
}
// Add thousand separators while user typing
private void inputAmount_TextChanged(object sender, EventArgs e)
{
if (!string.IsNullOrEmpty(inputAmount.Text))
{
System.Globalization.CultureInfo culture = new System.Globalization.CultureInfo("en-US");
int valueBefore = Int32.Parse(inputAmount.Text, System.Globalization.NumberStyles.AllowThousands);
inputAmount.Text = String.Format(culture, "{0:N0}", valueBefore);
inputAmount.Select(inputAmount.Text.Length, 0);
}
}

Check with int.TryParse whether the input text is a number .
Then add the inputAmount string with the current character and convert it to the desired format.
Then place the CaretIndex at the end of the control with inputAmount.SelectionStart.
The following code shows how to do this
private void inputAmount_KeyPress(object sender, KeyPressEventArgs e)
{
int number = 0;
bool success = int.TryParse(e.KeyChar.ToString(), out number);
if (success)
{
string input = (inputAmount.Text + e.KeyChar).Replace(",", "");
inputAmount.Text = String.Format("{0:n0}", Convert.ToInt32(input));
inputAmount.SelectionStart = inputAmount.Text.Length;
e.Handled = true;
}
}

How to Constraint on TextBox in C#?

I try constraint for TextBox in C#. I succesfull this for users can put only numbers:
private void TxtID_KeyPress(object sender, KeyPressEventArgs e)
{
e.Handled = !char.IsDigit(e.KeyChar) && !char.IsControl(e.KeyChar);
}
Now, I wonder how can users just write 11 char in TextBox? I try char.Max or Min but i can't in the KeyPress event.

Something like this:
public MyForm()
{
InitializeComponent();
// At most 11 characters
TxtID.MaxLength = 11;
}
private void TxtID_KeyPress(object sender, KeyPressEventArgs e)
{
// char.IsDigit is too wide: it returns true on any unicode digit (e.g. Persian ones)
e.Handled = (e.KeyChar < '0' || e.KeyChar > '9') && !char.IsControl(e.KeyChar);
}
// On Paste we should validate the input:
// what if user copy "bla-bla-bla 1234" and paste it to TxtID?
private void TxtID_TextChanged(object sender, EventArgs e)
{
Control ctrl = (sender as Control);
string value = string.Concat(ctrl
.Text
.Where(c => c >= '0' && c <= '9'));
if (value != ctrl.Text)
ctrl.Text = value;
}

can't determine '.' keychar for a textbox KeyPress event

I use below code to not allowing any character except numbers in a textbox ... but it allows '.' character! I don't want it to allow dot.
private void txtJustNumber_KeyPress(object sender, KeyPressEventArgs e)
{
if (!char.IsDigit((char)(e.KeyChar)) &&
e.KeyChar != ((char)(Keys.Enter)) &&
e.KeyChar != (char)(Keys.Delete) &&
e.KeyChar != (char)(Keys.Back)&&
e.KeyChar !=(char)(Keys.OemPeriod))
{
e.Handled = true;
}
}

use this:
if (!char.IsDigit((char)(e.KeyChar)) &&
e.KeyChar != ((char)(Keys.Enter)) &&
(e.KeyChar != (char)(Keys.Delete) || e.KeyChar == Char.Parse(".")) &&
e.KeyChar != (char)(Keys.Back)
)
it is because Keys.Delete's char value is 46 which is the same as '.'. I do not know why it likes this.

You could try this instead (where textBox1 would be your textbox):
// Hook up the text changed event.
textBox1.TextChanged += textBox1_TextChanged;
...
private void textBox1_TextChanged(object sender, EventArgs e)
{
// Replace all non-digit char's with empty string.
textBox1.Text = Regex.Replace(textBox1.Text, #"[^\d]", "");
}
Or
// Save the regular expression object globally (so it won't be created every time the text is changed).
Regex reg = new Regex(#"[^\d]");
private void textBox1_TextChanged(object sender, EventArgs e)
{
if (reg.IsMatch(textBox1.Text))
textBox1.Text = reg.Replace(textBox1.Text, ""); // Replace only if it matches.
}

//This is the shortest way
private void txtJustNumber_KeyPress(object sender, KeyPressEventArgs e)
{
if(!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar))
{
e.Handled = true;
}
}

try this code for your problem in keypress event :
private void txtMazaneh_KeyPress(object sender, KeyPressEventArgs e)
{
if (!char.IsDigit(e.KeyChar) && (int)e.KeyChar != 8 ||(e.KeyChar= .))
e.Handled = true;
}

How to stop the first character in a text box from being '.'?

This is the code I currently have:
private void textBox_KeyPress(object sender, KeyPressEventArgs e)
{
e.Handled = !char.IsDigit(e.KeyChar) && !char.IsControl(e.KeyChar) && e.KeyChar != '.';
if (e.KeyChar == '.' && (sender as TextBox).Text.IndexOf('.') > -1) e.Handled = true;
}

KeyPress isn't good enough to do this kind of validation. A simple way to bypass it is to paste text into the text box with Ctrl+V. Or the context menu, no key event at all.
In this specific case, the TextChanged event will get the job done:
private void textBox_TextChanged(object sender, EventArgs e) {
var box = (TextBox)sender;
if (box.Text.StartsWith(".")) box.Text = "";
}
But there's a lot more to validating numeric values. You also need to reject stuff like 1.1.1 or 1.-2 etcetera. Use the Validating event instead. Drop an ErrorProvider on the form and implement the event like this:
private void textBox_Validating(object sender, CancelEventArgs e) {
var box = (TextBox)sender;
decimal value;
if (decimal.TryParse(box.Text, out value)) errorProvider1.SetError(box, "");
else {
e.Cancel = true;
box.SelectAll();
errorProvider1.SetError(box, "Invalid number");
}
}

You probably want to use the TextChanged event, since the user could paste in values. For the best experience given the requirements, I'd suggest simply removing any leading . characters.
void textBox1_TextChanged(object sender, EventArgs e)
{
if (textBox1.Text.StartsWith("."))
{
textBox1.Text = new string(textBox1.Text.SkipWhile(c => c == '.').ToArray());
}
}
This does not address a requirement to use only digits -- wasn't clear in the question if that is the case.

This works for copy and pasting too.
private void textBox1_KeyUp(object sender, KeyEventArgs e)
{
int decimalCount=0;
string rebuildText="";
for(int i=0; i<textBox1.Text.Length; i++)
{
if (textBox1.Text[i] == '.')
{
if (i == 0) break;
if (decimalCount == 0)
rebuildText += textBox1.Text[i];
decimalCount++;
}
else if ("0123456789".Contains(textBox1.Text[i]))
rebuildText += textBox1.Text[i];
}
textBox1.Text = rebuildText;
textBox1.SelectionStart = textBox1.Text.Length;
}

You can try this:
private void TextBox_TextChanged(object sender, EventArgs e)
{
TextBox.Text = TextBox.Text.TrimStart('.');
}

How to make a TextBox accept only alphabetic characters?

How can I make a TextBox only accept alphabetic characters with spaces?

You could use the following snippet:
private void textBox1_TextChanged(object sender, EventArgs e)
{
if (!System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text, "^[a-zA-Z ]"))
{
MessageBox.Show("This textbox accepts only alphabetical characters");
textBox1.Text.Remove(textBox1.Text.Length - 1);
}
}

You can try by handling the KeyPress event for the textbox
void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
e.Handled = !(char.IsLetter(e.KeyChar) || e.KeyChar == (char)Keys.Back);
}
Additionally say allow backspace in case you want to remove some text, this should work perfectly fine for you
EDIT
The above code won't work for paste in the field for which i believe you will have to use TextChanged event but then it would be a bit more complicated with you having to remove the incorrect char or highlight it and place the cursor for the user to make the correction Or maybe you could validate once the user has entered the complete text and tabs off the control.

private void textbox1_KeyDown_1(object sender, KeyEventArgs e)
{
if (e.Key >= Key.A && e.Key <= Key.Z)
{
}
else
{
e.Handled = true;
}
}

The simplest way is to handle the TextChangedEvent and check what's been typed:
string oldText = string.Empty;
private void textBox2_TextChanged(object sender, EventArgs e)
{
if (textBox2.Text.All(chr => char.IsLetter(chr)))
{
oldText = textBox2.Text;
textBox2.Text = oldText;
textBox2.BackColor = System.Drawing.Color.White;
textBox2.ForeColor = System.Drawing.Color.Black;
}
else
{
textBox2.Text = oldText;
textBox2.BackColor = System.Drawing.Color.Red;
textBox2.ForeColor = System.Drawing.Color.White;
}
textBox2.SelectionStart = textBox2.Text.Length;
}
This is a regex-free version if you prefer. It will make the text box blink on bad input.
Please note that it also seems to support paste operations as well.

Write Code in Text_KeyPress Event as
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (!char.IsLetter(e.KeyChar))
{
e.Handled = true;
}
}

This one is working absolutely fine...
private void manufacturerOrSupplierTextBox_KeyPress(object sender, KeyPressEventArgs e)
{
if (char.IsControl(e.KeyChar) || char.IsLetter(e.KeyChar))
{
return;
}
e.Handled = true;
}

This solution uses regular expressions, does not allow invalid characters to be pasted into the text box and maintains the cursor position.
using System.Text.RegularExpressions;
int CursorWas;
string WhatItWas;
private void textBox1_Enter(object sender, EventArgs e)
{
WhatItWas = textBox1.Text;
}
private void textBox1_TextChanged(object sender, EventArgs e)
{
if (Regex.IsMatch(textBox1.Text, "^[a-zA-Z ]*$"))
{
WhatItWas = textBox1.Text;
}
else
{
CursorWas = textBox1.SelectionStart == 0 ? 0 : textBox1.SelectionStart - 1;
textBox1.Text = WhatItWas;
textBox1.SelectionStart = CursorWas;
}
}
Note: textBox1_TextChanged recursive call.

if (System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text, "^[a-zA-Z]+$"))
{
}
else
{
textBox1.Text = textBox1.Text.Remove(textBox1.Text.Length - 1);
MessageBox.Show("Enter only Alphabets");
}
Please Try this

private void textBox2_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar >= '0' && e.KeyChar <= '9')
e.Handled = true;
else
e.Handled = false;
}

Try This
private void tbCustomerName_KeyPress(object sender, KeyPressEventArgs e)
{
e.Handled = !(char.IsLetter(e.KeyChar) || e.KeyChar == (char)Keys.Back||e.KeyChar==(char)Keys.Space);
}
It Allows White Spaces Too

you can try following code that alert at the time of key press event
private void tbOwnerName_KeyPress(object sender, KeyPressEventArgs e)
{
//===================to accept only charactrs & space/backspace=============================================
if (e.Handled = !(char.IsLetter(e.KeyChar) || e.KeyChar == (char)Keys.Back || e.KeyChar == (char)Keys.Space))
{
e.Handled = true;
base.OnKeyPress(e);
MessageBox.Show("enter characters only");
}

Here is my solution and it works as planned:
string errmsg = "ERROR : Wrong input";
ErrorLbl.Text = errmsg;
if (e.Handled = !(char.IsLetter(e.KeyChar) || e.KeyChar == (char)Keys.Back || e.KeyChar == (char)Keys.Space))
{
ErrorLbl.Text = "ERROR : Wrong input";
}
else ErrorLbl.Text = string.Empty;
if (ErrorLbl.Text == errmsg)
{
Nametxt.Text = string.Empty;
}

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (!char.IsControl(e.KeyChar) && !char.IsLetter(e.KeyChar) &&
(e.KeyChar !='.'))
{
e.Handled = true;
MessageBox.Show("Only Alphabets");
}
}

Try following code in KeyPress event of textbox
if (char.IsLetter(e.KeyChar) == false &
Convert.ToString(e.KeyChar) != Microsoft.VisualBasic.Constants.vbBack)
e.Handled = true

works for me, even though not the simplest one.
private void Alpha_Click(object sender, EventArgs e)
{
int count = 0;
foreach (char letter in inputTXT.Text)
{
if (Char.IsLetter(letter))
{
count++;
}
else
{
count = 0;
}
}
if (count != inputTXT.Text.Length)
{
errorBox.Text = "The input text must contain only alphabetic characters";
}
else
{
errorBox.Text = "";
}
}

This works fine as far as characters restriction, Any suggestions on error msg prompt with my code if it's not C OR L
Private Sub TXTBOX_TextChanged(sender As System.Object, e As System.EventArgs) Handles TXTBOX.TextChanged
Dim allowed As String = "C,L"
For Each C As Char In TXTBOX.Text
If allowed.Contains(C) = False Then
TXTBOX.Text = TXTBOX.Text.Remove(TXTBOX.SelectionStart - 1, 1)
TXTBOX.Select(TXTBOX.Text.Count, 0)
End If
Next
End Sub

Try this one. Spaces and shortcut keys work
if (!char.IsControl(e.KeyChar) && !char.IsLetter(e.KeyChar) && !char.IsSeparator(e.KeyChar))
{
e.Handled = true;
}