Masking

gistfile1.cs

using System;
using System.Linq;
using System.Text.RegularExpressions;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using CCWin.Core.Extensions;

namespace CCWin.App.Infrastructure.Behaviours
{
    /// <summary>
    /// Provides masking behavior for any <see cref="TextBox"/>.
    /// </summary>
    /// <remarks>
    /// Taken from a StackOverflow answer: http://stackoverflow.com/questions/1103765/wpf-textbox-how-to-define-some-restriction
    /// </remarks>
    public static class Masking
    {
        private static readonly DependencyPropertyKey _maskExpressionPropertyKey =
            DependencyProperty.RegisterAttachedReadOnly("MaskExpression",
            typeof(Regex), typeof(Masking), new FrameworkPropertyMetadata());

        /// <summary>
        /// Identifies the <see cref="Mask"/> dependency property.
        /// </summary>
        public static readonly DependencyProperty MaskProperty =
            DependencyProperty.RegisterAttached("Mask", typeof(string), typeof(Masking), new FrameworkPropertyMetadata(OnMaskChanged));

        /// <summary>
        /// Identifies the <see cref="MaskExpression"/> dependency property.
        /// </summary>
        public static readonly DependencyProperty MaskExpressionProperty = _maskExpressionPropertyKey.DependencyProperty;

        /// <summary>
        /// Gets the mask for a given <see cref="TextBox"/>.
        /// </summary>
        /// <param name="textBox">
        /// The <see cref="TextBox"/> whose mask is to be retrieved.
        /// </param>
        /// <returns>
        /// The mask, or <see langword="null"/> if no mask has been set.
        /// </returns>
        public static string GetMask(TextBox textBox)
        {
            if (textBox == null)
            {
                throw new ArgumentNullException("textBox");
            }

            return textBox.GetValue(MaskProperty) as string;
        }

        /// <summary>
        /// Sets the mask for a given <see cref="TextBox"/>.
        /// </summary>
        /// <param name="textBox">
        /// The <see cref="TextBox"/> whose mask is to be set.
        /// </param>
        /// <param name="mask">
        /// The mask to set, or <see langword="null"/> to remove any existing mask from <paramref name="textBox"/>.
        /// </param>
        public static void SetMask(TextBox textBox, string mask)
        {
            if (textBox == null)
            {
                throw new ArgumentNullException("textBox");
            }

            textBox.SetValue(MaskProperty, mask);
        }

        /// <summary>
        /// Gets the mask expression for the <see cref="TextBox"/>.
        /// </summary>
        /// <remarks>
        /// This method can be used to retrieve the actual <see cref="Regex"/> instance created as a result of setting the mask on a <see cref="TextBox"/>.
        /// </remarks>
        /// <param name="textBox">
        /// The <see cref="TextBox"/> whose mask expression is to be retrieved.
        /// </param>
        /// <returns>
        /// The mask expression as an instance of <see cref="Regex"/>, or <see langword="null"/> if no mask has been applied to <paramref name="textBox"/>.
        /// </returns>
        public static Regex GetMaskExpression(TextBox textBox)
        {
            if (textBox == null)
            {
                throw new ArgumentNullException("textBox");
            }

            return textBox.GetValue(MaskExpressionProperty) as Regex;
        }

        private static void SetMaskExpression(TextBox textBox, Regex regex)
        {
            textBox.SetValue(_maskExpressionPropertyKey, regex);
        }

        private static void OnMaskChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
        {
            var textBox = dependencyObject as TextBox;
            var mask = e.NewValue as string;
            textBox.PreviewTextInput -= textBox_PreviewTextInput;
            textBox.PreviewKeyDown -= textBox_PreviewKeyDown;
            DataObject.RemovePastingHandler(textBox, Pasting);

            if (mask == null)
            {
                textBox.ClearValue(MaskProperty);
                textBox.ClearValue(MaskExpressionProperty);
            }
            else
            {
                textBox.SetValue(MaskProperty, mask);
                SetMaskExpression(textBox, new Regex(mask, RegexOptions.Compiled | RegexOptions.IgnorePatternWhitespace));
                textBox.PreviewTextInput += textBox_PreviewTextInput;
                textBox.PreviewKeyDown += textBox_PreviewKeyDown;
                DataObject.AddPastingHandler(textBox, Pasting);
            }
        }

        private static void textBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
        {
            var textBox = sender as TextBox;
            var maskExpression = GetMaskExpression(textBox);

            if (maskExpression == null)
            {
                return;
            }

            var proposedText = GetProposedText(textBox, e.Text);

            if (!maskExpression.IsMatch(proposedText))
            {
                e.Handled = true;
            }
        }

        private static void textBox_PreviewKeyDown(object sender, KeyEventArgs e)
        {
            var textBox = sender as TextBox;
            var maskExpression = GetMaskExpression(textBox);

            if (maskExpression == null)
            {
                return;
            }

            //pressing space doesn't raise PreviewTextInput - no idea why, but we need to handle
            //explicitly here
            if (e.Key == Key.Space)
            {
                var proposedText = GetProposedText(textBox, " ");

                if (!maskExpression.IsMatch(proposedText))
                {
                    e.Handled = true;
                }
            }
        }

        private static void Pasting(object sender, DataObjectPastingEventArgs e)
        {
            var textBox = sender as TextBox;
            var maskExpression = GetMaskExpression(textBox);

            if (maskExpression == null)
            {
                return;
            }

            if (e.DataObject.GetDataPresent(typeof(string)))
            {
                var pastedText = e.DataObject.GetData(typeof(string)) as string;
                var proposedText = GetProposedText(textBox, pastedText);

                if (!maskExpression.IsMatch(proposedText))
                {
                    e.CancelCommand();
                }
            }
            else
            {
                e.CancelCommand();
            }
        }

        /// <summary>
        /// Yikes - in .net 4.0 you can't believe the Text Property. If you bind a decimal to a textbox and enter '25.' and have
        /// UpdateSourceTrigger = PropertyChanged, the textbox displays '25.' but its Text property returns as '25'.
        /// This is broken from .net 3.5 (it's actually coz of the changes to the data binding pipeline).
        /// Hence the nasty Enumerable.Range crap in this method to get what the textbox is actually displaying :o(
        /// </summary>
        /// <param name="textBox">The text box.</param>
        /// <param name="newText">The new text.</param>
        /// <returns></returns>
        private static string GetProposedText(TextBox textBox, string newText)
        {
            var text = Enumerable.Range(0, textBox.LineCount).Aggregate("", (s, i) => s + textBox.GetLineText(i) + (textBox.LineCount - 1 > i ? Environment.NewLine : ""));

            if (textBox.SelectionStart != -1)
            {
                text = text.Remove(textBox.SelectionStart, textBox.SelectionLength);
            }

            text = text.Insert(textBox.CaretIndex, newText);

            return text;
        }
    }
}