WPF Numerical TextBox with Math Operations

• Download source code - 17.2 KB

Introduction

The NumberTextBox class filters its input to allow only numbers. In addition, if the user types +-*/, then a context menu opens which allows the entry of a second number (operand). The context menu displays the result as the user types, allowing the user to either accept the result or cancel it.

Both the normal number keys and the keypad are supported. The result can be accepted either by clicking on it with the mouse or by using the Enter key.

The zip archive includes the NumberTextBox class plus a simple test application.

The NumberTextBox Class

using System;
using System.Text.RegularExpressions;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media.Imaging;

namespace WpfApplication1
{
    /// <summary>
    /// A WPF custom <see cref="System.Windows.Controls.TextBox">TextBox</see> for editing numbers.
    /// </summary>
    public class NumberTextBox : TextBox
    {
        public NumberTextBox()
            : base()
        {
            PreviewTextInput += OnPreviewTextInput;
        }

        private static Regex regexDisallowedInteger = 
        new Regex(@"[^0-9-]+");  // matches disallowed text
        private static Regex regexDisallowedFloat = 
        new Regex(@"[^0-9-+.,e]+");  // matches disallowed text

        private void OnPreviewTextInput(object sender, TextCompositionEventArgs e)
        {
            if (Text.Length > 0 && OpenMathMenu(e.Text))
                e.Handled = true;
            else
                e.Handled = regexDisallowedFloat.IsMatch(e.Text);  // or regexDisallowedInteger
        }

        #region Math

        private enum EOperation { Add, Subtract, Multiply, Divide }
        private EOperation operation = EOperation.Add;
        private ContextMenu menuMath = null;
        private MenuItem miOperand = null;
        private MenuItem miResult = null;

        private bool OpenMathMenu(string text)
        {
            if (menuMath != null)
                return false;

            if (text == "+" || text == "-" || 
            text == "*" || text == "/")
            {
                if (text == "-" && CaretIndex == 0)  // negative sign in front of number
                    return false;

                miOperand = new MenuItem();
                miOperand.Header = "";
                miOperand.FontSize = 18;
                miOperand.FontWeight = FontWeights.Medium;
                miOperand.IsEnabled = false;

                if (text == "+")
                {
                    operation = EOperation.Add;
                    miOperand.Icon = new Image 
                    { Source = new BitmapImage(new Uri("Images/operator_add.png", UriKind.Relative)) };
                }
                else if (text == "-")
                {
                    operation = EOperation.Subtract;
                    miOperand.Icon = new Image 
                    { Source = new BitmapImage(new Uri("Images/operator_sub.png", UriKind.Relative)) };
                }
                else if (text == "*")
                {
                    operation = EOperation.Multiply;
                    miOperand.Icon = new Image 
                    { Source = new BitmapImage(new Uri("Images/operator_mult.png", UriKind.Relative)) };
                }
                else if (text == "/")
                {
                    operation = EOperation.Divide;
                    miOperand.Icon = new Image 
                    { Source = new BitmapImage(new Uri("Images/operator_div.png", UriKind.Relative)) };
                }

                miResult = new MenuItem();
                miResult.Header = "";
                miResult.Icon = new Image 
                { Source = new BitmapImage(new Uri("Images/operator_equals.png", UriKind.Relative)) };
                miResult.FontSize = 18;
                miResult.FontWeight = FontWeights.Medium;
                miResult.IsEnabled = false;
                miResult.Click += OnResultClick;

                menuMath = new ContextMenu();
                menuMath.Items.Add(miOperand);
                menuMath.Items.Add(new Separator());
                menuMath.Items.Add(miResult);
                menuMath.PlacementTarget = this;
                menuMath.Placement = System.Windows.Controls.Primitives.PlacementMode.Bottom;
                menuMath.PreviewKeyDown += OnMathPreviewKeyDown;
                menuMath.Closed += OnMathClosed;
                menuMath.IsOpen = true;
                return true;
            }

            return false;
        }

        private void OnMathPreviewKeyDown(object sender, KeyEventArgs e)
        {
            if (Keyboard.IsKeyDown(Key.LeftShift) || Keyboard.IsKeyDown(Key.RightShift))
                return;

            string operand = miOperand.Header.ToString();
            //System.Diagnostics.Debug.WriteLine
            (string.Format("OnMathPreviewKeyDown {0}", e.Key.ToString()));
            switch (e.Key)
            {
                case Key.Cancel:
                case Key.Clear:
                case Key.Escape:
                case Key.OemClear:
                    miResult.Header = "";
                    OnResultClick(this, null);
                    break;

                case Key.Back:
                case Key.Delete:
                    if (operand.Length > 0)
                        UpdateResult(operand.Substring(0, operand.Length - 1));
                    else
                        OnResultClick(this, null);
                    break;

                case Key.LineFeed:
                case Key.Enter:
                    OnResultClick(this, null);
                    break;

                case Key.OemPlus:  // '='
                    OnResultClick(this, null);
                    break;

                case Key.Subtract:
                case Key.OemMinus:
                    if (operand.Length == 0)
                        miOperand.Header = "-";
                    break;

                case Key.D0:
                case Key.D1:
                case Key.D2:
                case Key.D3:
                case Key.D4:
                case Key.D5:
                case Key.D6:
                case Key.D7:
                case Key.D8:
                case Key.D9:
                    char key1 = (char)((e.Key - Key.D0) + '0');
                    if (char.IsDigit(key1))
                        UpdateResult(operand + key1);
                    break;

                case Key.NumPad0:
                case Key.NumPad1:
                case Key.NumPad2:
                case Key.NumPad3:
                case Key.NumPad4:
                case Key.NumPad5:
                case Key.NumPad6:
                case Key.NumPad7:
                case Key.NumPad8:
                case Key.NumPad9:
                    char key2 = (char)((e.Key - Key.NumPad0) + '0');
                    if (char.IsDigit(key2))
                        UpdateResult(operand + key2);
                    break;

                case Key.OemComma:
                    if (!operand.Contains(","))
                        miOperand.Header = operand + ",";
                    break;

                case Key.Decimal:
                case Key.OemPeriod:
                    if (!operand.Contains("."))
                        miOperand.Header = operand + ".";
                    break;

                //case Key.Multiply:
                //case Key.Add:
                //case Key.Divide:
            }
        }

        private void UpdateResult(string operand)
        {
            miOperand.Header = operand;
            double dop1, dop2, result;
            if (double.TryParse(Text, out dop1) && double.TryParse(operand, out dop2))
            {
                switch (operation)
                {
                    case EOperation.Add:
                        result = dop1 + dop2;
                        miResult.Header = result.ToString();
                        miResult.IsEnabled = true;
                        break;

                    case EOperation.Subtract:
                        result = dop1 - dop2;
                        miResult.Header = result.ToString();
                        miResult.IsEnabled = true;
                        break;

                    case EOperation.Multiply:
                        result = dop1 * dop2;
                        miResult.Header = result.ToString();
                        miResult.IsEnabled = true;
                        break;

                    case EOperation.Divide:
                        if (dop2 == 0.0)
                        {
                            miResult.Header = "";
                            miResult.IsEnabled = false;
                        }
                        else
                        {
                            result = dop1 / dop2;
                            if (double.IsInfinity(result) || double.IsNaN(result))
                            {
                                miResult.Header = "";
                                miResult.IsEnabled = false;
                            }
                            else
                            {
                                miResult.Header = result.ToString();
                                miResult.IsEnabled = true;
                            }
                        }
                        break;
                }
            }
            else
            {
                miResult.Header = "";
                miResult.IsEnabled = false;
            }
        }

        private void OnResultClick(object sender, RoutedEventArgs e)
        {
            string result = miResult.Header.ToString();
            if (result.Length > 0)
            {
                Text = result;
                CaretIndex = Text.Length;
            }

            menuMath.IsOpen = false;
        }

        private void OnMathClosed(object sender, RoutedEventArgs e)
        {
            menuMath.PreviewKeyDown -= OnMathPreviewKeyDown;
            menuMath.Closed -= OnMathClosed;
            miResult.Click -= OnResultClick;

            menuMath = null;
            miOperand = null;
            miResult = null;
        }

        #endregion Math
    }
}