Question

I tryed to create my own numeric textbox here is my code:

public class NumericTextBox : TextBox
{

    public NumericTextBox()
        : base()
    {
        this.Text = "0";
    }

    private void HandleKeyEvent(KeyEventArgs e)
    {
        e.Handled = true;
        if ((Keyboard.Modifiers & ModifierKeys.Alt) != 0)
        {
            return;
        }
        if (e.Key == Key.Back || e.Key == Key.Delete || e.Key == Key.Left || e.Key == Key.Right ||
            e.Key == Key.D0 || e.Key == Key.D1 || e.Key == Key.D2 || e.Key == Key.D3 || e.Key == Key.D4 || e.Key == Key.D5 || e.Key == Key.D6 ||
            e.Key == Key.D7 || e.Key == Key.D8 || e.Key == Key.D9 ||
            e.Key == Key.NumPad0 || e.Key == Key.NumPad1 || e.Key == Key.NumPad2 || e.Key == Key.NumPad3 || e.Key == Key.NumPad4 || e.Key == Key.NumPad5 || e.Key == Key.NumPad6 ||
            e.Key == Key.NumPad7 || e.Key == Key.NumPad8 || e.Key == Key.NumPad9)
        {
            e.Handled = false;
        }
        else if ((e.Key == Key.Subtract || (e.Key == Key.Unknown && e.PlatformKeyCode == 189)) && base.SelectionStart == 0 && (base.Text.Length == 0 || base.Text[0] != '-'))
        {
            e.Handled = false;
        }
    }

    protected override void OnKeyDown(KeyEventArgs e)
    {
        HandleKeyEvent(e);
        base.OnKeyDown(e);
    }

    protected override void OnKeyUp(KeyEventArgs e)
    {
        HandleKeyEvent(e);
        base.OnKeyUp(e);
    }
}

everything works like supposed but if you press alt and some numbers it creates the ascii symbol corresponding to the number.. is there any way to block an “alt + number combination?
it seems that alt + key just gets entered without going threw OnKeyUp or OnKeyDown…

Answer 1

I got it working by using the TextChanged event here is my code…

public class NumericTextBox : TextBox
{

    int value;

    public NumericTextBox()
        : base()
    {
        this.Text = "0";
        this.TextChanged += new TextChangedEventHandler(NumericTextBox_TextChanged);
    }

    void NumericTextBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        int selectionStart = base.SelectionStart;
        bool changed = false;
        List<char> charList = new List<char>();
        for (int i = 0; i < base.Text.Length; i++)
        {
            if (IsValidChar(base.Text[i], i))
            {
                charList.Add(base.Text[i]);
            }
            else
            {
                if (selectionStart >= i)
                {
                    selectionStart--;
                }
                changed = true;
            }
        }
        if (changed)
        {
            string text = new string(charList.ToArray());
            this.Text = text;
            this.SelectionStart = selectionStart;
        }
        int newValue;
        if (!int.TryParse(this.Text, out newValue))
        {
            this.Text = value.ToString();
            this.SelectionStart = this.Text.Length;
        }
        else
        {
            value = newValue;
        }
    }

    private bool IsValidChar(char c, int index)
    {
        return ((c == '-' && index == 0) || c == '0' || c == '1' || c == '2' || c == '3' || c == '4' || c == '5' || c == '6' || c == '7' || c == '8' || c == '9');
    }

    private void HandleKeyEvent(KeyEventArgs e)
    {
        e.Handled = true;
        if ((Keyboard.Modifiers & ModifierKeys.Control) == ModifierKeys.Control)
        {
            e.Handled = false;
        }
        if (e.Key == Key.Back || e.Key == Key.Delete || e.Key == Key.Left || e.Key == Key.Right ||
            e.Key == Key.D0 || e.Key == Key.D1 || e.Key == Key.D2 || e.Key == Key.D3 || e.Key == Key.D4 || e.Key == Key.D5 || e.Key == Key.D6 ||
            e.Key == Key.D7 || e.Key == Key.D8 || e.Key == Key.D9 ||
            e.Key == Key.NumPad0 || e.Key == Key.NumPad1 || e.Key == Key.NumPad2 || e.Key == Key.NumPad3 || e.Key == Key.NumPad4 || e.Key == Key.NumPad5 || e.Key == Key.NumPad6 ||
            e.Key == Key.NumPad7 || e.Key == Key.NumPad8 || e.Key == Key.NumPad9)
        {
            e.Handled = false;
        }
        else if ((e.Key == Key.Subtract || (e.Key == Key.Unknown && e.PlatformKeyCode == 189)) && base.SelectionStart == 0 && (base.Text.Length == 0 || base.Text[0] != '-'))
        {
            e.Handled = false;
        }
    }

    protected override void OnKeyDown(KeyEventArgs e)
    {
        HandleKeyEvent(e);
        base.OnKeyDown(e);
    }

    protected override void OnKeyUp(KeyEventArgs e)
    {
        HandleKeyEvent(e);
        base.OnKeyUp(e);
    }
}