Validating decimal number on PreviewTextInput of TextBox

Question

I need to validate a valid decimal number entry in WPF TextBox. It should block all the other characters.

 private void PreviewTextInput(object sender, TextCompositionEventArgs e)
 {
    // Here I should write to validate whether a decimal or integer number 
    // is enter and restrict all other invalid characters.
 }

[What have you tried?](http://www.whathaveyoutried.com) What didn't work? Where are you blocking? — Cyril Gandon, Oct 23 '13 at 07:52
Have a look at http://stackoverflow.com/questions/16914224/wpf-textbox-to-enter-decimal-values — fen89, Oct 23 '13 at 07:58

score 1 · Answer 1 · answered Oct 23 '13 at 07:51

Not sure if that's what you mean, but here is a code to check if it's possible to parse the string to either integer or decimal value:

private void txtBox_PreviewTextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)
{
    int number;
    decimal dnumber;
    if (int.TryParse(txtBox.Text, out number) || decimal.TryParse(txtBox.Text, out dnumber))
    {
        //process further if true
    }
}

score 1 · Answer 2 · answered Oct 23 '13 at 07:59

i use a behavior for this stuff atm

xaml usage:

    <TextBox>
        <i:Interaction.Behaviors>
            <Behaviors:TextBoxInputBehavior InputMode="DecimalInput" JustPositivDecimalInput="false"/>
        </i:Interaction.Behaviors>
    </TextBox>

behavior.cs

public class TextBoxInputBehavior : Behavior<TextBox>
{
    const NumberStyles validNumberStyles = NumberStyles.AllowDecimalPoint |
                                               NumberStyles.AllowThousands |
                                               NumberStyles.AllowLeadingSign;
    public TextBoxInputBehavior()
    {
        this.InputMode = TextBoxInputMode.None;
        this.JustPositivDecimalInput = false;
    }

    public TextBoxInputMode InputMode { get; set; }


    public static readonly DependencyProperty JustPositivDecimalInputProperty =
     DependencyProperty.Register("JustPositivDecimalInput", typeof(bool),
     typeof(TextBoxInputBehavior), new FrameworkPropertyMetadata(false));

    public bool JustPositivDecimalInput
    {
        get { return (bool)GetValue(JustPositivDecimalInputProperty); }
        set { SetValue(JustPositivDecimalInputProperty, value); }
    }

    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.PreviewTextInput += AssociatedObjectPreviewTextInput;
        AssociatedObject.PreviewKeyDown += AssociatedObjectPreviewKeyDown;

        DataObject.AddPastingHandler(AssociatedObject, Pasting);

    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.PreviewTextInput -= AssociatedObjectPreviewTextInput;
        AssociatedObject.PreviewKeyDown -= AssociatedObjectPreviewKeyDown;

        DataObject.RemovePastingHandler(AssociatedObject, Pasting);
    }

    private void Pasting(object sender, DataObjectPastingEventArgs e)
    {
        if (e.DataObject.GetDataPresent(typeof(string)))
        {
            var pastedText = (string)e.DataObject.GetData(typeof(string));

            if (!this.IsValidInput(this.GetText(pastedText)))
            {
                System.Media.SystemSounds.Beep.Play();
                e.CancelCommand();
            }
        }
        else
        {
            System.Media.SystemSounds.Beep.Play();
            e.CancelCommand();
        }
    }

    private void AssociatedObjectPreviewKeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Space)
        {
            if (!this.IsValidInput(this.GetText(" ")))
            {
                System.Media.SystemSounds.Beep.Play();
                e.Handled = true;
            }
        }
    }

    private void AssociatedObjectPreviewTextInput(object sender, TextCompositionEventArgs e)
    {
        if (!this.IsValidInput(this.GetText(e.Text)))
        {
            System.Media.SystemSounds.Beep.Play();
            e.Handled = true;
        }
    }

    private string GetText(string input)
    {
        var txt = this.AssociatedObject;

        int selectionStart = txt.SelectionStart;
        if (txt.Text.Length < selectionStart) 
            selectionStart = txt.Text.Length;

        int selectionLength = txt.SelectionLength;
        if (txt.Text.Length < selectionStart + selectionLength) 
            selectionLength = txt.Text.Length - selectionStart;

        var realtext = txt.Text.Remove(selectionStart, selectionLength);

        int caretIndex = txt.CaretIndex;
        if (realtext.Length < caretIndex) 
            caretIndex = realtext.Length;

        var newtext = realtext.Insert(caretIndex, input);

        return newtext;
    }

    private bool IsValidInput(string input)
    {
        switch (InputMode)
        {
            case TextBoxInputMode.None:
                return true;
            case TextBoxInputMode.DigitInput:
                return CheckIsDigit(input);

            case TextBoxInputMode.DecimalInput:
                decimal d;
                //wen mehr als ein Komma
                if (input.ToCharArray().Where(x => x == ',').Count() > 1)
                    return false;

                if (input.Contains("-"))
                {
                    if (this.JustPositivDecimalInput) 
                        return false;

                    //minus einmal am anfang zulässig
                    if (input.IndexOf("-",StringComparison.Ordinal) == 0  && input.ToCharArray().Count(x=>x=='-') == 1)
                        return true;
                }

                var result = decimal.TryParse(input, validNumberStyles, CultureInfo.CurrentCulture, out d);
                return result;



            default: throw new ArgumentException("Unknown TextBoxInputMode");

        }
        return true;
    }

    private bool CheckIsDigit(string wert)
    {
        return wert.ToCharArray().All(Char.IsDigit);
    }
}

public enum TextBoxInputMode
{
    None,
    DecimalInput,
    DigitInput
}

Validating decimal number on PreviewTextInput of TextBox

2 Answers2