WPF, MVVM design lengthy binding consideration - wpf

Question

I am currently writing a WPF application, using a MVVM approach and Entity Framework.
In my MainVindow.xaml, I have a navigation system on the left.
For each of its navigation items, there is a corresponding user control.
Clicking on one of its items displays the user control on the right of the main window.
I have a view model for each user control.
I bind my MainWindow.xaml to an instance of my MainViewModel class.
Each user control is binded to an instance of its corresponding viewmodel which is stored in my MainViewModel class.
In the constructor of each of these user controls viewmodels, I pass the MainViewModel.
The idea is to share an entity amongst all these viewmodels:
class MainViewModel
{
public SharedEntity MySharedEntity
{
get
{
return _mySharedEntity;
}
set
{
InpcLogic(_mySharedEntity);
}
}
public FirstUserControlViewModel MyFirstUserControlViewModel
{
get
{
if (_myFirstUserControlViewModel == null)
_myFirstUserControlViewModel = new FirstUserControlViewModel(this);
return _myFirstUserControlViewModel;
}
}
}
This way, in the FirstUserControlViewModel instance, I can access MySharedEntity this way:
class FirstUserControlViewModel
{
MainViewModel _mainViewModel;
public MainViewModel MyMainViewModel
{
get
{
return _mainViewModel;
}
}
public SharedEntity MyMainViewmodelSharedEntity
{
get
{
return _mainViewModel.MySharedEntity;
}
}
public FirstUserControlViewModel(MainViewModel mainViewModel)
{
_mainViewModel = mainViewModel;
}
}
In my user control xaml (which is binded to the view model above), I can bind controls to this shared entity from my mainViewModel.
Now, here is my problem: When I change the shared entity from anywhere in the application, the bindings are not always refreshed on the user control level. Could it be due due to the fact that the INPC logic is in the main view model and not the user control view model?
Let's say I bind a textblock in my first user control like so:
<TextBox Text="{Binding MyMainViewModel.MySharedEntity.AnyStringMember,
Mode=TwoWay,
UpdateSourceTrigger=PropertyChanged}" />
It works fine.
However, if I do the following
<TextBox Text="{Binding MyMainViewmodelSharedEntity.AnyStringMember,
Mode=TwoWay,
UpdateSourceTrigger=PropertyChanged}" />
Then, bindings do not refresh when I change the shared entity. It uses the same reference to my entity in both cases, doesn't it?
**
UPDATE
**
Here's what I'll end up doing:
In my MainViewModel, I have the following property:
public class MainViewModel
{
EntityFrameworkClass _myPrivateEfObject;
EntityFrameworkNavigationPropertyClass _myPrivateEfNavigationPropertyObject;
public EntityFrameworkClass MyPublicEfObject
{
get
{
return _myPrivateEfObject;
}
set
{
InpcLogic(ref _myPrivateEfObject, value);
MyPublicEfNavigationPropertyObject = _myPrivateEfObject.EntityFrameworkNavigationPropertyClass.FirstOrDefault();
}
}
public EntityFrameworkNavigationPropertyClass MyPublicEfNavigationPropertyObject
{
get
{
return _myPrivateEfNavigationPropertyObject;
}
set
{
InpcLogic(ref _myPrivateEfNavigationPropertyObject, value);
}
}
}
Then in my user control xaml, I simply use MainViewModel.MyPublicEfNavigationPropertyObject

Answer 1

You need to call the method that implements INotifyPropertyChanged. In your case, you want it implemented to your MySharedEntity then on the setter of the AnyStringMember you want to RaisePropertyChanged.

Answer 2

I am binding my textbox to a property which does not implement any INPC behavior. Yes, it refers to the same object, but if there is no INPC behavior implemented, the graphical component can't be notified that it needs to refresh.
I am going to bind to properties within my MainViewModel and implement INPC in there.