JRCookbook/JRCookbookControls/JRCookbookNumericTextBox.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace JRCookbookControls
{
    [System.Serializable()]
    public class JRCookbookNumericTextBox: TextBox
    {
        private String _strLastValue = String.Empty;
        private bool _blnAllowNegative = true;
        private bool _blnAllowDecimal = true;
        private bool _blnAllowEmpty = true;

        public JRCookbookNumericTextBox()
        {
            this.TextChanged += new System.EventHandler(this.NumericTextBox_TextChanged);
            this.Validating += new System.ComponentModel.CancelEventHandler(this.NumericTextBox_Validating);
        }

        [DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
        public bool AllowDecimal
        {
            get
            {
                return _blnAllowDecimal;
            }
            set
            {
                _blnAllowDecimal = value;
            }

        }

        [DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
        public bool AllowNegative
        {
            get
            {
                return _blnAllowNegative;
            }
            set
            {
                _blnAllowNegative = value;
            }

        }

        [DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
        public bool AllowEmpty
        {
            get
            {
                return _blnAllowEmpty;
            }
            set
            {
                _blnAllowEmpty = value;
            }

        }

        private void NumericTextBox_TextChanged(System.Object sender, System.EventArgs e)
        {
            bool blnValueIsOK = true;
            Int32 intPosition = 0;
            bool blnAlreadySeenDecimal = false;

            //Allow digits, one decimal point, and minus sign (if first character only)
            foreach (char chrCharacter in this.Text)
            {
                switch (chrCharacter)
                {
                    case char x when (x >= '0' && x <= '9'):
                            //OK
                        break;
                    case '-':
                        if (intPosition > 0 || AllowNegative == false)
                        {
                            blnValueIsOK = false;
                        }
                        break;
                    case '.':
                        if (blnAlreadySeenDecimal)
                        {
                            blnValueIsOK = false;
                        }
                        else
                        {
                            blnAlreadySeenDecimal = true;
                        }
                        break;
                    default:
                        blnValueIsOK = false;
                        break;
                }

                intPosition += 1;

                if (!blnValueIsOK)
                {
                    break;
                }

            }

            if (blnValueIsOK)
            {
                _strLastValue = this.Text;
            }
            else
            {
                Int32 oldSelectionStart = this.SelectionStart - 1;
                this.Text = _strLastValue;
                if (oldSelectionStart >= 0 && oldSelectionStart <= this.Text.Length)
                {
                    this.SelectionStart = oldSelectionStart;
                }
            }

        }

        private void NumericTextBox_Validating(System.Object sender, System.ComponentModel.CancelEventArgs e)
        {
            if (this.Text == String.Empty)
            {
                if (AllowEmpty)
                {
                    return;
                }
                else
                {
                    e.Cancel = true;
                }
            }

            //Now that we know it's not empty, make sure we have a digit
            foreach (char chrCharacter in this.Text)
            {
                switch (chrCharacter)
                {
                    case char x when (x >= '0' && x <= '9'):
                        //OK
                        return;
                }
            }

            //If we got here, we have hyphen or period, but no digits
            e.Cancel = true;
        }

    }

}