Text Box Numeric Entry

Question

I would like to enter numeric only input to more than one textBox. Instead of repeating the same code (as I have done in my sample attached code) for each Box, could I have one method for all?

using System;  
using System.Collections.Generic;  
using System.ComponentModel;  
using System.Data;  
using System.Drawing;  
using System.Linq;  
using System.Text;  
using System.Windows.Forms;  
  
namespace TestingNumericInput  
{  
    public partial class Form1 : Form  
    {  
        public Form1()  
        {  
            InitializeComponent();  
        }  
  
        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)  
        {  
            if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) &&  
                (e.KeyChar != '.'))  
            {  
                e.Handled = true;  
            }  
  
            // only allow one decimal point  
            if ((e.KeyChar == '.') && ((sender as TextBox).Text.IndexOf('.') > -1))  
            {  
                e.Handled = true;  
            }  
        }  
  
        private void textBox1_TextChanged(object sender, EventArgs e)  
        {  
            if (textBox1.Text.FirstOrDefault() == '.')  
            {  
                textBox1.Text = "0" + textBox1.Text;  
                textBox1.Select(textBox1.Text.Length, 0);  
            }  
        }  
  
        private void textBox2_KeyPress(object sender, KeyPressEventArgs e)  
        {  
            if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) &&  
                (e.KeyChar != '.'))  
            {  
                e.Handled = true;  
            }  
  
            // only allow one decimal point  
            if ((e.KeyChar == '.') && ((sender as TextBox).Text.IndexOf('.') > -1))  
            {  
                e.Handled = true;  
            }  
        }  
  
        private void textBox2_TextChanged(object sender, EventArgs e)  
        {  
            if (textBox2.Text.FirstOrDefault() == '.')  
            {  
                textBox2.Text = "0" + textBox2.Text;  
                textBox2.Select(textBox2.Text.Length, 0);  
            }  
        }  
  
          
    }  
}  
  

Answer 1

(the windows-app-sdk-text-rendering tag is wrong, it should be dotnet-csharp or winforms...)

Derive a Class , like :

public class MyTextBox : System.Windows.Forms.TextBox  
{  
    // code...  
}  

Answer 2

Use a dedicated number TextBox as shown below.

public class NumericTextBox : TextBox  
{  
    private readonly char _decimalSeparator =  
        CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator[0];  
  
    public NumericTextBox()  
    {  
        TextAlign = HorizontalAlignment.Right;  
    }  
  
    protected override void OnKeyPress(KeyPressEventArgs e)  
    {  
  
        if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && e.KeyChar != _decimalSeparator)  
        {  
            e.Handled = true;  
        }  
  
        if (e.KeyChar == _decimalSeparator && Text.IndexOf(_decimalSeparator) > -1)  
        {  
            e.Handled = true;  
        }  
  
        base.OnKeyPress(e);  
  
    }  
  
    [Browsable(false)]  
    public int Integer => int.TryParse(Text, out var value) ? value : 0;  
    [Browsable(false)]  
    public decimal Decimal => decimal.TryParse(Text, out var value) ? value : 0;  
    [Browsable(false)]  
    public double Double => double.TryParse(Text, out var value) ? value : 0;  
  
    public bool HasValue() => !string.IsNullOrWhiteSpace(Text);  
  
    int WM_PASTE = 0x0302;  
    protected override void WndProc(ref Message message)  
    {  
        if (message.Msg == WM_PASTE)  
        {  
            var clipboardData = Clipboard.GetDataObject();  
            var input = (string)clipboardData?.GetData(typeof(string))!;  
            int count = 0;  
  
            foreach (var c in input)  
            {  
                if (c == _decimalSeparator)  
                {  
                    count++;  
                    if (count > 1)  
                    {  
                        return;  
                    }  
                }  
            }  
  
            foreach (var character in input)  
            {  
  
                if (!char.IsControl(character) && !char.IsDigit(character) && character != _decimalSeparator)  
                {  
                    message.Result = (IntPtr)0;  
                    return;  
                }  
  
            }  
        }  
  
        base.WndProc(ref message);  
  
    }  
}  

To get numbers from the above use the properties Integer Decimal or Double and to determine if the value is 0 use HasValue