Costum UserControl in DataTemlate set property doesnt work!

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C#

WPF

I built user control with DependencyProperty like this:

public string SelectedString{
    get { return (string)GetValue(SelectedClientProperty); }
    set { SetValue(SelectedClientProperty, value); InvokePropertyChanged("SelectedString"); }
}

// Using a DependencyProperty as the backing store for SelectedString.  This enables animation, styling, binding, etc...
public static readonly DependencyProperty SelectedStringProperty =
    DependencyProperty.Register("SelectedString", typeof(string), typeof(MyUserContol),
    new FrameworkPropertyMetadata(OnSelectedStringPropertyChanged));

private static void OnSelectedStringPropertyChanged(DependencyObject source,
                                                     DependencyPropertyChangedEventArgs e)
{
    (source as MyUserContol).SelectedSatringChanged();
}

and when i use it , its working good, here:

<UserContol:MyUserControl SelectedClient="blabla" />

but in dataTemplate it dosnt work! here:

<DataGrid1:DataGrid x:Name="dg"   ItemsSource="{Binding MyDataTable}">
    <DataGrid1:DataGrid.Columns>
        <DataGrid1:DataGridTemplateColumn SortMemberPath="[Client]" Header="Date" >
            <DataGrid1:DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <UserContol:MyUserControl SelectedClient="blabla" >
                </DataTemplate>
            </DataGrid1:DataGridTemplateColumn.CellTemplate>
    </DataGrid1:DataGrid.Columns>

</DataGrid1:DataGrid>

its not Changing the DependencyProperty to "blabla", i know it because the OnSelectedStringPropertyChanged doesnt invoke!

(its not working in listView to...)

can someone help me with this, please??