Textbox Content string, but want only numbers when entering characters in textbox

Question

I am very new to programming and mainly am doing it as a hobby, but I have made a few small executable programs to help me with my work (little industry specific calculators.

On to the question, I have a textbox with a content shown before focus, which I would like to keep, but also I would like to allow only numbers to be entered, is there any way of doing this.

Sorry, should have added, the content before focus is a string. — Dan Luxford, Mar 01 '17 at 13:16
Possible duplicate of [How do I get a TextBox to only accept numeric input in WPF?](http://stackoverflow.com/questions/1268552/how-do-i-get-a-textbox-to-only-accept-numeric-input-in-wpf) — Tobias Theel, Mar 01 '17 at 13:20
You can try putting TextMode="Number" to your textbox control. See if this one works for you. if not you will have to use a validator. — jmag, Mar 01 '17 at 13:21
Read the possible duplicate, and also read the comments below the marked answer. There is valuable info there, for example handling the space (It can be done using PreviewKeyDown property) — Kamil Solecki, Mar 01 '17 at 13:23

score 1 · Answer 1 · answered Mar 01 '17 at 13:25

1

Try adding PreviewTextInput event handler to your TextBox.

textBox1.PreviewTextInput += new TextCompositionEventHandler(textBox1_PreviewTextInput);

In your event handler test if entered character is digit.

private void textBox1_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
    if (!char.IsDigit(e.Text, e.Text.Length - 1))
        e.Handled = true;
}

answered Mar 01 '17 at 13:25

Gabriel

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This has worked perfectly. Thank you for taking the time to answer my query. – Dan Luxford Mar 02 '17 at 15:13
That's good, @DanLuxford I will be happy if you will accept my answer with green check mark :-) – Gabriel Mar 03 '17 at 06:02

score 0 · Answer 2 · answered Mar 01 '17 at 14:48

If you want to avoid using code-behind, you can convert the above answer into a behavior by creating a class (e.g. DigitsOnlyBehavior) that contains an AttachedProperty. When the attached property is set, you register the handler which is defined and implemented in your behavior class.

One short example:

public static class MyBehavior
{
  public static readonly DependencyProperty AllowOnlyDigitsProperty = DependencyProperty.RegisterAttached(
    "AllowOnlyDigits", typeof(bool), typeof(MyBehavior), new PropertyMetadata(default(bool), OnAllowOnlyDigitsChanged));

  private static void OnAllowOnlyDigitsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
  {
    var textBox = d as TextBox;
    if (textBox == null) return;
    textBox.PreviewTextInput += PreviewTextBoxInput;
  }

  public static void SetAllowOnlyDigits(DependencyObject element, bool value)
  {
    element.SetValue(AllowOnlyDigitsProperty, value);
  }

  private static void PreviewTextBoxInput(object sender, TextCompositionEventArgs e)
  {
    var textbox = sender as TextBox;

    if (!char.IsDigit(e.Text, e.Text.Length - 1))
      e.Handled = true;
  }


  public static bool GetAllowOnlyDigits(DependencyObject element)
  {
    return (bool) element.GetValue(AllowOnlyDigitsProperty);
  }
}

As you can see the PreviewTextBoxInput function is mainly what the previous post suggests.

You can now "attach" that behavior in your XAML like this:

    <TextBox local:MyBehavior.AllowOnlyDigits="True" />

This solution is not fully complete, since it does not support changing the property (it will attach the handler each time the property changes, so it assumes you only set it once via XAML). But if you don't want to change this behavior during runtime, you're fine.

Hi Markus. I have gone with the answer above, for the simple reason that it looks a lot less daunting for someone of my level of inexperience. — Dan Luxford, Mar 02 '17 at 15:18
That's good also. Many developers that I've met using WPF try to minimize the code inside the "Code Behind" of the views. — Markus Palcer, Mar 17 '17 at 08:05

Textbox Content string, but want only numbers when entering characters in textbox

2 Answers2