Numeric Only TextBox

Question

I've looked all over the place, but it seems that examples I have seen allow only numbers 0-9

I'm writing a Pythagorean Theorem program. I wish to have the phone (Windows Phone 7) check if there are ANY alpha (A-Z, a-z), symbols (@,%), or anything other than a number in the textbox. If not, then it will continue computing. I want to check so there will be no future errors.

This is basically a bad pseudocode of what I want it to do

txtOne-->any alpha?--No-->any symbols--No-->continue...

I would actually prefer a command to check if the string is completely a number.

Thanks in advance!

Answer 1

There are several ways to do this:

1. You can use TryParse() and check if the return value is not false.

2. You can use Regex to validate:

   Match match = Regex.Match(textBox.Text, @"^\d+$");
   if (match.Success) { ... }
   // or
   if (Regex.IsMatch(textBox.Text, @"^\d+$")) { ... }
   

Answer 2

An even better way to ensure that your textbox is a number is to handle the KeyPress event. You can then choose what characters you want to allow. In the following example we disallow all characters that are not digits:

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    // If the character is not a digit, don't let it show up in the textbox.
    if (!char.IsDigit(e.KeyChar))
        e.Handled = true;
}

This ensures that your textbox text is a number because it only allows digits to be entered.

---

This is something I just came up with to allow decimal values (and apparently the backspace key):

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (char.IsDigit(e.KeyChar))
    {
        return;
    }
    if (e.KeyChar == (char)Keys.Back)
    {
        return;
    }
    if (e.KeyChar == '.' && !textBox1.Text.Contains('.'))
    {
        return;
    }
    e.Handled = true;
} 

Answer 3

Or you can simply only give them the Numeric keyboard. There are several different keyboard layouts you can use. Link

If you want to do more indepth, I have used the KeyDown and KeyUp events to check what was entered and handle the keypress. Link

Answer 4

You can define the textbox's input scope.

Example:

<TextBox InputScope="Digits"></TextBox>

Answer 5

You can use TryParse and see if there is a result.

See http://msdn.microsoft.com/en-us/library/system.int64.tryparse.aspx

Int64 output;
if (!Int64.TryParse(input, out output)
{
    ShowErrorMessage();
    return
}
Continue..

Answer 6

/// <summary>
/// A numeric-only textbox.
/// </summary>
public class NumericOnlyTextBox : TextBox
{
    #region Properties

    #region AllowDecimals

    /// <summary>
    /// Gets or sets a value indicating whether [allow decimals].
    /// </summary>
    /// <value>
    ///   <c>true</c> if [allow decimals]; otherwise, <c>false</c>.
    /// </value>
    public bool AllowDecimals
    {
        get { return (bool)GetValue(AllowDecimalsProperty); }
        set { SetValue(AllowDecimalsProperty, value); }
    }

    /// <summary>
    /// The allow decimals property
    /// </summary>
    public static readonly DependencyProperty AllowDecimalsProperty =
        DependencyProperty.Register("AllowDecimals", typeof(bool), 
        typeof(NumericOnlyTextBox), new UIPropertyMetadata(false));

    #endregion

    #region MaxValue

    /// <summary>
    /// Gets or sets the max value.
    /// </summary>
    /// <value>
    /// The max value.
    /// </value>
    public double? MaxValue
    {
        get { return (double?)GetValue(MaxValueProperty); }
        set { SetValue(MaxValueProperty, value); }
    }

    /// <summary>
    /// The max value property
    /// </summary>
    public static readonly DependencyProperty MaxValueProperty =
        DependencyProperty.Register("MaxValue", typeof(double?), 
        typeof(NumericOnlyTextBox), new UIPropertyMetadata(null));

    #endregion

    #region MinValue

    /// <summary>
    /// Gets or sets the min value.
    /// </summary>
    /// <value>
    /// The min value.
    /// </value>
    public double? MinValue
    {
        get { return (double?)GetValue(MinValueProperty); }
        set { SetValue(MinValueProperty, value); }
    }

    /// <summary>
    /// The min value property
    /// </summary>
    public static readonly DependencyProperty MinValueProperty =
        DependencyProperty.Register("MinValue", typeof(double?), 
        typeof(NumericOnlyTextBox), new UIPropertyMetadata(null));

    #endregion

    #endregion

    #region Contructors

    /// <summary>
    /// Initializes a new instance of the <see cref="NumericOnlyTextBox" /> class.
    /// </summary>
    public NumericOnlyTextBox()
    {
        this.PreviewTextInput += OnPreviewTextInput;        
    }

    #endregion

    #region Methods

    /// <summary>
    /// Numeric-Only text field.
    /// </summary>
    /// <param name="text">The text.</param>
    /// <returns></returns>
    public bool NumericOnlyCheck(string text)
    {
        // regex that matches disallowed text
        var regex = (AllowDecimals) ? new Regex("[^0-9.]+") : new Regex("[^0-9]+");
        return !regex.IsMatch(text);
    }

    #endregion

    #region Events

    /// <summary>
    /// Called when [preview text input].
    /// </summary>
    /// <param name="sender">The sender.</param>
    /// <param name="e">The <see cref="TextCompositionEventArgs" /> instance 
    /// containing the event data.</param>
    /// <exception cref="System.NotImplementedException"></exception>
    private void OnPreviewTextInput(object sender, TextCompositionEventArgs e)
    {
        // Check number
        if (this.NumericOnlyCheck(e.Text))
        {
            // Evaluate min value
            if (MinValue != null && Convert.ToDouble(this.Text + e.Text) < MinValue)
            {
                this.Text = MinValue.ToString();
                this.SelectionStart = this.Text.Length;
                e.Handled = true;
            }

            // Evaluate max value
            if (MaxValue != null && Convert.ToDouble(this.Text + e.Text) > MaxValue)
            {
                this.Text = MaxValue.ToString();
                this.SelectionStart = this.Text.Length;
                e.Handled = true;
            }
        }

        else
        {
            e.Handled = true;
        }
    }

    #endregion
}