WPF DateTimePicker user control

I've created a UserControl that should act as a control inside a Window:

XAML:
























































XAML.CS

`public partial class DateTimePicker : UserControl, INotifyPropertyChanged
{
public DateTimePicker()
{
InitializeComponent();
(Content as FrameworkElement).DataContext = this;
}

#region SelectedTime

public DateTime? SelectedDateTime
{
get
{
return (DateTime?)GetValue(SelectedDateTimeProperty);
}
set
{
SetValue(SelectedDateTimeProperty, value);
}
}

public static readonly DependencyProperty
SelectedDateTimeProperty =
DependencyProperty.Register("SelectedDateTime",
typeof(DateTime?),
typeof(DateTimePicker));

#endregion

private bool _isPopupOpen;
public bool IsPopupOpen
{
get { return _isPopupOpen; }
set
{
SetProperty(ref _isPopupOpen, value);
}
}

#region INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged = delegate { };

protected virtual void SetProperty(ref T member, T va

You have used two types of bindings:

1. Binding between your control and the usage DataContext

This binding is fine and is the way how WPF binding system was supposed to work with respect to the MVVM pattern.

1. Bindings between xaml controls and the xaml class (Same class which is the parent of those controls)

The interactions between xaml controls and xaml code-behind are not supposed to flow through the same MVVM pattern. This is why in the partial class you have the possibility to access directly your controls.

Example from xaml:

Example from code-behind:

void ButtonChangeStatus_OnClick(object sender, RoutedEventArgs e)
{
    IsPopupOpen = !IsPopupOpen;
    ButtonChangeStatus.Background = Brushes.Green;
}

Another drawback could be the usage of some properties from outside of your implementation. Suppose there is some logic which needs to open the popup without a click on the ButtonChangeStatus button but from a click which originates outside of your implementation. To achieve such behavior the user of your control would need to bind IsOpen to his DataContext. But in the current implementation it's not possible without a great confusion (you need to have two IsOpen dependency properties); it will be possible by exposing the IsOpen dependency property to the outside ViewModel in the same way as you already did with SelectedDateTime. Having both a local IsOpen property and a dependency one will allow you to handle the Popup using two sources.

StackExchange Code Review Q#98905, answer score: 3