WPF DependencyProperty Register Default Value

WPF > DependencyProperty > Register > Default Value

public static readonly DependencyProperty

UpdateSourceTriggerProperty = DependencyProperty.Register("UpdateSourceTrigger", typeof(UpdateSourceTrigger),

typeof(TextBox),

new FrameworkPropertyMetadata(UpdateSourceTrigger.LostFocus)); // add your default value here

WPF DependencyProperty Example

WPF > Windows > DependencyProperty 

DependencyProperty is a property that can be set through methods such as, styling, data binding, animation, and inheritance.

Example: Create a numeric TextBox with DependencyProperty 

Create new WPF User Control Library

NumericTextBox.xaml

<TextBox x:Class="NumericTextBox.NumericTextBox"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
          >
</TextBox>

 NumericTextBox.xaml.cs

using System;

using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace NumericTextBox
{
    /// <summary>
    /// Interaction logic for NumericTextBox.xaml
    /// </summary>
    public partial class NumericTextBox : TextBox
    {
        public NumericTextBox()
        {
            InitializeComponent();
            this.PreviewTextInput += OnPreviewTextInput;
        }

        /// <summary>
        /// The max value property
        /// </summary>

        public static readonly DependencyProperty MaxValueProperty =

            DependencyProperty.Register("MaxValue", typeof(double?),
            typeof(NumericTextBox), new UIPropertyMetadata(null));

        public double? MaxValue

        {
            get { return (double?)GetValue(MaxValueProperty); }
            set { SetValue(MaxValueProperty, value); }
        }

        /// <summary>

        /// The min value property
        /// </summary>

        public static readonly DependencyProperty MinValueProperty =

            DependencyProperty.Register("MinValue", typeof(double?),
            typeof(NumericTextBox), new UIPropertyMetadata(null));

        public double? MinValue

        {
            get { return (double?)GetValue(MinValueProperty); }
            set { SetValue(MinValueProperty, value); }
        }

        private bool CheckNumeric(string text)

        {
             var regex = new Regex("[^0-9.]+");
            return !regex.IsMatch(text);
        }

        private void OnPreviewTextInput(object sender, TextCompositionEventArgs e)
        {
            if (this.CheckNumeric(e.Text))
            {
                if (e.Text == "." && this.Text.Contains("."))
                    e.Handled = true;
                else
                {
                    // Check min value
                    if (MinValue != null && Convert.ToDouble(this.Text + e.Text) < MinValue)
                    {
                        this.Text = MinValue.ToString();
                        this.SelectionStart = this.Text.Length;
                        e.Handled = true;
                    }

                    // Check 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;
        }
    }
}

MainWindow.xaml

You can set MinValue and MaxValue properties

<Window

        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

        xmlns:NumericTextBox="clr-namespace:NumericTextBox;assembly=NumericTextBox" x:Class="WpfApplication3.MainWindow"

        Title="MainWindow" Height="350" Width="525">

    <Grid>

        <NumericTextBox:NumericTextBox HorizontalAlignment="Left" Margin="98,89,0,0" TextWrapping="Wrap" Text="" VerticalAlignment="Top"

                                     Width="201" MinValue="1" MaxValue="100000"/>

    </Grid>

</Window>