Question

I’m trying to understand WPF in details. So far I don’t know how work 2 things:

1.Where Dependency Property (DP) is stored?

My guesses: DP is static, so this object (DP) is same for all objects that are derived from class, that have this DP. I suppose that DP has its own storage, where DP saves values for all objects that use this DP. Mb sth like dictionary…

2.How the Grid can assign an object (for example Button) to its own row (in details)?

My guesses:

Button Grid.Row="1" (in XAML)

SetRow (from Grid) will be executed. PropertyChangedCallback (initialized in metadata) will be triggered also. I suppose that Grid will assign Button by some code in this Callback, but it makes no sense for me… Callback will get DepedencyObject (= Grid instance) and EventArgs (= value). How grid can know which object changed Attached Dependency Property? Grid should have its own storage for objects position… How does Grid save that information?

Thanks in advance for explanation.

Answer 1

1. Right, there are static dictionaries of some kind that associate the objects with their values (at various levels, styles, local values etc. The value is determined via precedence). The internals should not matter to you.
2. Wrong, the dependency object on which the property was set is passed to the callback, not the grid. (There is no grid instance to be found directly anyway, the grid instance then is found via VisualTreeHelper.GetParent). The mechanism probably works via looping through the Grid.Children during the layout pass and getting the properties of those to determine where everything should go.