WPF Custom TextBox with Decimal Formatting

Question

I am new to WPF. I have a requirement that I need to develop a custom textbox control which should support the functionality like:

1. Should accept only decimal

Answer 1

I have written a custom control which will have dependency property called ActualText. Bind your value into that ActualText property and manipulated the Text property of the textbox during the gotfocus and lostfocus event. Also validated for decimal number in the PreviewTextInput event. refer the below code.

 class TextBoxEx:TextBox
{
    public string ActualText
    {
        get { return (string)GetValue(ActualTextProperty); }
        set { SetValue(ActualTextProperty, value); }
    }

    // Using a DependencyProperty as the backing store for ActualText.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty ActualTextProperty =
        DependencyProperty.Register("ActualText", typeof(string), typeof(TextBoxEx), new PropertyMetadata(string.Empty, OnActualTextChanged));

    private static void OnActualTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        TextBox tx = d as TextBox;
        tx.Text = (string)e.NewValue;
        string str = tx.Text;            
        double dbl = Convert.ToDouble(str);
        str = string.Format("{0:0.###}", dbl);
        tx.Text = str;
    }

    public TextBoxEx()
    {
        this.GotFocus += TextBoxEx_GotFocus;
        this.LostFocus += TextBoxEx_LostFocus;
        this.PreviewTextInput += TextBoxEx_PreviewTextInput;
    }

    void TextBoxEx_PreviewTextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)
    {
        decimal d;
        if(!decimal.TryParse(e.Text,out d))
        {
            e.Handled = true;
        }
    }        

    void TextBoxEx_LostFocus(object sender, System.Windows.RoutedEventArgs e)
    {
        ConvertText();
    }

    void TextBoxEx_GotFocus(object sender, System.Windows.RoutedEventArgs e)
    {
        this.Text = ActualText;
    }

    private void ConvertText()
    {
        string str = this.Text;
        ActualText = str;
        double dbl = Convert.ToDouble(str);
        str = string.Format("{0:0.###}", dbl);
        this.Text = str;
    }
}