informing parent when child changes a property value

Question

I'm writing a simple calendar control for better understanding of WPF. I have a CalendarHeader control that contains two buttons (next,prevoious) and a dependency property CurrentMonth defined as

 public static DependencyProperty CurrentMonthProperty = DependencyProperty.Register
        ("CurrentMonth", typeof(int), typeof(CalendarHeader), new FrameworkPropertyMetadata(DateTime.Now.Month, FrameworkPropertyMetadataOptions.None, CurrentMonthChangedCallBack));

Another control that need so interact with CalenderHeader is CalendarMonth. To inform CalendarMonth when a month is changed in CalendarHeader, I'm adding an owner dependency property to it as

public static DependencyProperty CurrentMonthProperty = CalendarHeader.CurrentMonthProperty.AddOwner
        (typeof(CalendarMonth), new FrameworkPropertyMetadata(DateTime.Now.Month, CurrentMonthChangedCallBack));

When CalendarHeader changes the value of CurrentMonth, I thought it would also trigger the CurrentMonthChangedCallBack in CalendarMonth but it's not doing that. How can I inform CalendarMonth that the value of CurrentMonth in CalendarHeader is changed. Thanks a million

Answer 1

One option is to create a base control (let's call it CalendarPrimitive) to store the CurrentMonthProperty. When you register the property register with FrameworkPropertyMetadataOptions.Inherit.

If you derive CalendarHeaderControl and CalendarMonth control from the CalendarPrimitive, the value will automatically pass down the tree from CalendarHeader to CalendarMonth (assuming that CalendarMonth is nested within CalendarHeader).

Even better if your top level Calendar control also derives from CalendarPrimitive, It will be responsible for storing the CurrentMonthProperty and all of its Children will inherit the value.

Also, you probably want to define a CurrentMonthChanged RoutedEvent that a CalendarPrimitive can use to notify it's the top level that it has changed the CurrentMonth.

Your top level Calendar will listen for this Event and change its CurrentMonth accordingly (propagating the change down the tree).