Problem with understanding reference types

Question

I get from WCF service ObservableCoolection

MyTypes = e.Result;

ObservableCollection<MyType> MyTypes // it's a property of _myTypes

<telerik:RadGridView x:Name="grdSrL" ItemsSource="{Binding MyTypes}"  SelectedItem="{Binding SelectedMyType, Mode=TwoWay}"

public ShowroomLog SelectedMyType
{
    get { return _selectedMyType; }
    set
    {
        if (_selectedSMyType != value)
        {
            _selectedMyType = value;
            RaisePropertyChanged(SelectedMyTypePropertyName);
        }
    }
}

after I get those collection from web service, selected item is set by grid, and after that I do:

SelectedMyType = null;

Why after that none of item from collection isn't null?

if I do:

var x = new Car();
var y = x;

and

y = null;

then x would be also null;

Why there is different?

Answer 1

Reference types in C# are effectively object pointers. In your example x and y are object pointers, not the objects themselves. If you change a pointer you do not change the object. x would not also become null as you state. That assumption/example is incorrect.

If you called .Clear() on the collection via either variable, then both pointers to that collection will show 0 entries, but you need to explain what it is you are trying to do so I can explain with a specific example.

.Clear() would not however destroy any children in the list if there are referenced elsewhere (e.g. by another list).