C# DateTimePicker for WPF

DateTimePicker.xaml

<UserControl x:Class="Controls.DateTimePicker"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:sys="clr-namespace:System;assembly=mscorlib"
             mc:Ignorable="d">
    <UserControl.Resources>
        <ResourceDictionary>
            <controls:InvertBoolConverter x:Key="InvertBoolConverter" />
        </ResourceDictionary>
    </UserControl.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <ToggleButton Grid.Column="0" MinHeight="25" MinWidth="25" Name="PopUpCalendarButton" IsChecked="False" IsHitTestVisible="{Binding IsOpen, ElementName=CalendarPopup, Mode=OneWay, Converter={StaticResource InvertBoolConverter}}">
            <ToggleButton.Style>
                <Style TargetType="{x:Type ToggleButton}">
                    <Setter Property="Background" Value="White" />
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="{x:Type ToggleButton}">
                                <Border Background="{TemplateBinding Background}" BorderBrush="Black" BorderThickness="1">
                                    <ContentPresenter />
                                </Border>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </ToggleButton.Style>
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="2*" />
                    <ColumnDefinition Width="Auto" />
                </Grid.ColumnDefinitions>
                <TextBox BorderThickness="0" Height="26" x:Name="DateDisplay" VerticalAlignment="Center"
                         HorizontalAlignment="Left" VerticalContentAlignment="Center" HorizontalContentAlignment="Center"
                         IsHitTestVisible="False" IsReadOnly="True" IsUndoEnabled="False" />
                <Image Grid.Column="1" Name="CalIco" Stretch="Fill" HorizontalAlignment="Right" />
            </Grid>
        </ToggleButton>

        <Popup IsOpen="{Binding Path=IsChecked, ElementName=PopUpCalendarButton}" x:Name="CalendarPopup" PopupAnimation="Fade" StaysOpen="False" Width="180">
            <Border Padding="2" Background="White">
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="2*" />
                        <ColumnDefinition Width="2*" />
                        <ColumnDefinition Width="3*" />
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="*" />
                        <RowDefinition Height="Auto" />
                    </Grid.RowDefinitions>

                    <Calendar Grid.ColumnSpan="3" Margin="0,-3,0,0" x:Name="CalDisplay" DisplayDateStart="{Binding Source={x:Static sys:DateTime.Today}, Mode=OneWay}" SelectedDate="{x:Static sys:DateTime.Now}" PreviewMouseUp="CalDisplay_PreviewMouseUp" />
                    <ComboBox Grid.Row="1" Grid.Column="0" Name="Hours" HorizontalContentAlignment="Right" VerticalContentAlignment="Center" SelectedIndex="8" SelectionChanged="Time_SelectionChanged">
                        <ComboBoxItem Content="6" />
                        <ComboBoxItem Content="7" />
                        <ComboBoxItem Content="8" />
                        <ComboBoxItem Content="9" />
                        <ComboBoxItem Content="10" />
                        <ComboBoxItem Content="11" />
                        <ComboBoxItem Content="12" />
                        <ComboBoxItem Content="13" />
                        <ComboBoxItem Content="14" />
                        <ComboBoxItem Content="15" />
                        <ComboBoxItem Content="16" />
                        <ComboBoxItem Content="17" />
                        <ComboBoxItem Content="18" />
                    </ComboBox>
                    <ComboBox Grid.Row="1" Grid.Column="1" Name="Min" HorizontalContentAlignment="Right" VerticalContentAlignment="Center" SelectedIndex="0" SelectionChanged="Time_SelectionChanged">
                        <ComboBoxItem Content="0" />
                        <ComboBoxItem Content="10" />
                        <ComboBoxItem Content="20" />
                        <ComboBoxItem Content="30" />
                        <ComboBoxItem Content="40" />
                        <ComboBoxItem Content="50" />
                    </ComboBox>
                    <Button Grid.Row="1" Grid.Column="2" Name="SaveTime" Content="OK" Click="SaveTime_Click" />
                </Grid>
            </Border>
        </Popup>
    </Grid>
</UserControl>

DateTimePicker.xaml.cs

using System;
using System.Drawing;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Data;
using System.Windows.Input;
using System.Windows.Media.Imaging;

namespace Controls
{
    /// Changes and improvements made =>
    /// 1. Removed AM/PM chooser and made time selectable from 6:00 to 18:00
    /// 2. Popup improvements
    /// 3. Added SelectedDate DependencyProperty
    ///
    /// Things that will be needed for this control to work properly (and look good :) ) =>
    /// 1. A bitmap image 32x32 added as an embedded resource
    ///
    /// Licensing =>
    /// The Code Project Open License (CPOL)
    /// http://www.codeproject.com/info/cpol10.aspx

    public partial class DateTimePicker : UserControl
    {
        private const string DateTimeFormat = "dd.MM.yyyy HH:mm";

        #region "Properties"

        public DateTime SelectedDate
        {
            get => (DateTime)GetValue(SelectedDateProperty);
            set => SetValue(SelectedDateProperty, value);
        }

        #endregion

        #region "DependencyProperties"

        public static readonly DependencyProperty SelectedDateProperty = DependencyProperty.Register("SelectedDate",
            typeof(DateTime), typeof(DateTimePicker), new FrameworkPropertyMetadata(DateTime.Now, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

        #endregion

        public DateTimePicker()
        {
            InitializeComponent();
            CalDisplay.SelectedDatesChanged += CalDisplay_SelectedDatesChanged;
            CalDisplay.SelectedDate = DateTime.Now.AddDays(1);

            BitmapSource ConvertGDI_To_WPF(Bitmap bm)
            {
                BitmapSource bms = null;
                IntPtr h_bm = IntPtr.Zero;
                h_bm = bm.GetHbitmap();
                bms = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(h_bm, IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions());
                bms.Freeze();
                h_bm = IntPtr.Zero;
                return bms;
            }
            Bitmap bitmap1 = Properties.Resources.DateTimePicker;
            bitmap1.MakeTransparent(Color.Black);
            CalIco.Source = ConvertGDI_To_WPF(bitmap1);
        }

        #region "EventHandlers"

        private void CalDisplay_SelectedDatesChanged(object sender, EventArgs e)
        {
            var hours = (Hours?.SelectedItem as ComboBoxItem)?.Content?.ToString() ?? "0";
            var minutes = (Min?.SelectedItem as ComboBoxItem)?.Content?.ToString() ?? "0";
            TimeSpan timeSpan = TimeSpan.Parse(hours + ":" + minutes);
            if (CalDisplay.SelectedDate.Value.Date == DateTime.Today.Date && timeSpan.CompareTo(DateTime.Now.TimeOfDay) < 0)
            {
                timeSpan = TimeSpan.FromHours(DateTime.Now.Hour + 1);
            }
            var date = CalDisplay.SelectedDate.Value.Date + timeSpan;
            DateDisplay.Text = date.ToString(DateTimeFormat);
            SelectedDate = date;
        }

        private void SaveTime_Click(object sender, RoutedEventArgs e)
        {
            CalDisplay_SelectedDatesChanged(SaveTime, EventArgs.Empty);
            PopUpCalendarButton.IsChecked = false;
        }

        private void Time_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            CalDisplay_SelectedDatesChanged(sender, e);
        }

        private void CalDisplay_PreviewMouseUp(object sender, MouseButtonEventArgs e)
        {   // that it's not necessary to click twice after opening the calendar  https://stackoverflow.com/q/6024372
            if (Mouse.Captured is CalendarItem)
            {
                Mouse.Capture(null);
            }
        }

        #endregion
    }
    
    [ValueConversion(typeof(bool), typeof(bool))]
    public class InvertBoolConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (targetType != typeof(bool))
                throw new InvalidOperationException("The target must be a boolean");

            return !(bool)value;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (targetType != typeof(bool))
                throw new InvalidOperationException("The target must be a boolean");

            return !(bool)value;
        }
    }
}