Numeric Data Entry in WPF

Question

How are you handling the entry of numeric values in WPF applications?

Without a NumericUpDown control, I've been using a TextBox and handling its PreviewKeyDown event with the code below, but it's pretty ugly.

Has anyone found a more graceful way to get numeric data from the user without relying on a third-party control?

private void NumericEditPreviewKeyDown(object sender, KeyEventArgs e)
{
    bool isNumPadNumeric = (e.Key >= Key.NumPad0 && e.Key <= Key.NumPad9) || e.Key == Key.Decimal;
    bool isNumeric = (e.Key >= Key.D0 && e.Key <= Key.D9) || e.Key == Key.OemPeriod;

    if ((isNumeric || isNumPadNumeric) && Keyboard.Modifiers != ModifierKeys.None)
    {
        e.Handled = true;
        return;
    }

    bool isControl = ((Keyboard.Modifiers != ModifierKeys.None && Keyboard.Modifiers != ModifierKeys.Shift)
        || e.Key == Key.Back || e.Key == Key.Delete || e.Key == Key.Insert
        || e.Key == Key.Down || e.Key == Key.Left || e.Key == Key.Right || e.Key == Key.Up
        || e.Key == Key.Tab
        || e.Key == Key.PageDown || e.Key == Key.PageUp
        || e.Key == Key.Enter || e.Key == Key.Return || e.Key == Key.Escape
        || e.Key == Key.Home || e.Key == Key.End);

    e.Handled = !isControl && !isNumeric && !isNumPadNumeric;
}

Answer 1

How about:

protected override void OnPreviewTextInput(System.Windows.Input.TextCompositionEventArgs e)
{
    e.Handled = !AreAllValidNumericChars(e.Text);
    base.OnPreviewTextInput(e);
}

private bool AreAllValidNumericChars(string str)
{
    foreach(char c in str)
    {
        if(!Char.IsNumber(c)) return false;
    }

    return true;
}

Answer 2

This is how I do it. It uses a regular expression to check if the text that will be in the box is numeric or not.

Regex NumEx = new Regex(@"^-?\d*\.?\d*$");

private void TextBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
    if (sender is TextBox)
    {
        string text = (sender as TextBox).Text + e.Text;
        e.Handled = !NumEx.IsMatch(text);
    }
    else
        throw new NotImplementedException("TextBox_PreviewTextInput Can only Handle TextBoxes");
}

There is now a much better way to do this in WPF and Silverlight. If your control is bound to a property, all you have to do is change your binding statement a bit. Use the following for your binding:

<TextBox Text="{Binding Number, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}"/>

Note that you can use this on custom properties too, all you have to do is throw an exception if the value in the box is invalid and the control will get highlighted with a red border. If you click on the upper right of the red border then the exception message will pop up.

Answer 3

I've been using an attached property to allow the user to use the up and down keys to change the values in the text box. To use it, you just use

<TextBox local:TextBoxNumbers.SingleDelta="1">100</TextBox>

This doesn't actually address the validation issues that are referred to in this question, but it addresses what I do about not having a numeric up/down control. Using it for a little bit, I think I might actually like it better than the old numeric up/down control.

The code isn't perfect, but it handles the cases I needed it to handle:

• Up arrow, Down arrow
• Shift + Up arrow, Shift + Down arrow
• Page Up, Page Down
• Binding Converter on the text property

Code behind

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Input;

namespace Helpers
{
    public class TextBoxNumbers
    {    
        public static Decimal GetSingleDelta(DependencyObject obj)
        {
            return (Decimal)obj.GetValue(SingleDeltaProperty);
        }

        public static void SetSingleDelta(DependencyObject obj, Decimal value)
        {
            obj.SetValue(SingleDeltaProperty, value);
        }

        // Using a DependencyProperty as the backing store for SingleValue.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty SingleDeltaProperty =
            DependencyProperty.RegisterAttached("SingleDelta", typeof(Decimal), typeof(TextBoxNumbers), new UIPropertyMetadata(0.0m, new PropertyChangedCallback(f)));

        public static void f(DependencyObject o, DependencyPropertyChangedEventArgs e)
        {
            TextBox t = o as TextBox;

            if (t == null)
                return;

            t.PreviewKeyDown += new System.Windows.Input.KeyEventHandler(t_PreviewKeyDown);
        }

        private static Decimal GetSingleValue(DependencyObject obj)
        {
            return GetSingleDelta(obj);
        }

        private static Decimal GetDoubleValue(DependencyObject obj)
        {
            return GetSingleValue(obj) * 10;
        }

        private static Decimal GetTripleValue(DependencyObject obj)
        {
            return GetSingleValue(obj) * 100;
        }

        static void t_PreviewKeyDown(object sender, System.Windows.Input.KeyEventArgs e)
        {
            TextBox t = sender as TextBox;
            Decimal i;

            if (t == null)
                return;

            if (!Decimal.TryParse(t.Text, out i))
                return;

            switch (e.Key)
            {
                case System.Windows.Input.Key.Up:
                    if (Keyboard.Modifiers == ModifierKeys.Shift)
                        i += GetDoubleValue(t);
                    else
                        i += GetSingleValue(t);
                    break;

                case System.Windows.Input.Key.Down:
                    if (Keyboard.Modifiers == ModifierKeys.Shift)
                        i -= GetDoubleValue(t);
                    else
                        i -= GetSingleValue(t);
                    break;

                case System.Windows.Input.Key.PageUp:
                    i += GetTripleValue(t);
                    break;

                case System.Windows.Input.Key.PageDown:
                    i -= GetTripleValue(t);
                    break;

                default:
                    return;
            }

            if (BindingOperations.IsDataBound(t, TextBox.TextProperty))
            {
                try
                {
                    Binding binding = BindingOperations.GetBinding(t, TextBox.TextProperty);
                    t.Text = (string)binding.Converter.Convert(i, null, binding.ConverterParameter, binding.ConverterCulture);
                }
                catch
                {
                    t.Text = i.ToString();
                }
            }
            else
                t.Text = i.ToString();
        }
    }
}