Regex for wpf TextBox

Question

can someone help me to make regex for me?

• only numbers (positive and negative)
• only max one dot (optional)
• max precision 0.00 (optional)
• comma (,) should be replaced with dot (.)

Here is the code:

<TextBox PreviewTextInput="NumberValidationTextBox"/>

private void NumberValidationTextBox(object sender, TextCompositionEventArgs e)
        {
            Regex regex = new Regex("[^0-9.]+");
            e.Handled = regex.IsMatch(e.Text);
        }

Thanks.

Answer 1

The problem is in your method:

e.Text gives the character typed and not the content of TextBox

so this solution gives the result waited:

    private void NumberValidationTextBox(object sender, TextCompositionEventArgs e)
    {
        Regex regex = new Regex("^-?[0-9]*[\\.,]?[0-9]?[0-9]?$");
        var futureText = $"{(sender as TextBox).Text}{e.Text}";
        e.Handled = !regex.IsMatch(futureText);
    }

To replace , by . i suggest you to add the TextChanged event:

    private void OnTextChanged(object sender, TextChangedEventArgs e)
    {
        var myInput = sender as TextBox;

        myInput.Text = myInput.Text.Replace(",", ".").Trim();
        myInput.CaretIndex = myInput.Text.Length;
    }

---

   <TextBox PreviewTextInput="NumberValidationTextBox" TextChanged="OnTextChanged"/>

i play with the property CaretIndex to keep the Cursor in last position (Replace resets the position of Cursor in first position)

And i have added .trim() to myInput.Text = myInput.Text.Replace(",", ".").Trim(); because previewtextInput event doesnt play with space (its normal)