How to assign DataContext from parent View's ViewModel (Property) - wpf

Question

EDIT:
Here is a small sample Solution (VS 2013) showing my exact problem: nakkvarr.net/TestApp.zip
I have two views:
MainView
EmployeeView
I want my EmployeeView to reference the MainViewModel property "employees".
I tried this:
<DockPanel DataContext="{Binding DataContext.MainViewModel,
RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type EmployeeLisViewModel}}}">
But all I get is the Error: EmployeeListViewModel ist not supported in WPF ?!
(EmployeeListViewModel is also the name of the property of my MainViewModel)
The thing is:
My MainView has some menu items. One is for sorting the employee list, which is inside my UserControl. My UserControl ViewModel contains the Commands for sorting.
EDIT:
I changed it to vm:EmployeeListViewModel ... now the error is gone...but now I don't seem to get access to the ViewModel :/
<ia:InvokeCommandAction Command="{Binding LoadEmployeesCommand}"
Does not trigger, no emplyees get loaded. When I use the ViewModel directly, it works just fine.
MainWindow.xaml
<Window x:Class="de.XXX.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:controls="clr-namespace:de.XXX.Views"
xmlns:vm="clr-namespace:de.XXX.ViewModel"
Icon="/Images/App.ico"
Style="{StaticResource MainWindowStyle}"
Title="MainWindow">
<DockPanel DataContext="{Binding MainViewModel, Source={StaticResource Locator}}">
<Menu DockPanel.Dock="Top">
...
</Menu>
<controls:EmployeeListView DockPanel.Dock="Bottom" DataContext="{Binding EmployeeListViewModel}" />
</DockPanel>
</Window>
EmployeeListView.xaml //not model, copy & paste error x_X
<UserControl x:Class="de.XXX.Views.EmployeeListView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:vm="clr-namespace:de.XXX.ViewModel"
xmlns:ia="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
mc:Ignorable="d"
d:DesignHeight="350" d:DesignWidth="350">
<DockPanel DataContext="{Binding MainViewModel,
RelativeSource={RelativeSource FindAncestor,
AncestorType={x:Type vm:EmployeeListViewModel}}}">
<ListBox DockPanel.Dock="Bottom" x:Name="EmployeeList" ItemsSource="{Binding EmployeeList}" ScrollViewer.CanContentScroll="False" />
<ia:Interaction.Triggers>
<ia:EventTrigger EventName="Loaded">
<ia:InvokeCommandAction Command="{Binding LoadEmployeesCommand}" />
</ia:EventTrigger>
</ia:Interaction.Triggers>
</DockPanel>
</UserControl>

Answer 1

If you modify your SubControl to below, this should work.
<Grid DataContext="{Binding Path=DataContext.SubVM, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}">
I have a hint on what you are trying to achieve and I guess you have missed some details on Binding especially on other underlying properties needed to be set. This part is working based on the given code. But then, there are numerous ways in making it better. Good luck.

Answer 2

I think there might be a combination of misunderstandings here! Your UserControl has
x:Class="de.XXX.Views.EmployeeListView"
defined as the class name in xaml. However, you're also saying that the file is named EmployeeListViewModel.xaml? A .xaml file should never be named a viewmodel. I believe you should have MainWindow.xaml, EmployeeListView.xaml, MainWindowViewModel.cs, and EmployeeListViewModel.cs, is this the case?
Also, in your MainWindow.xaml, you're already setting the datacontext of your EmployeeListView usercontrol:
<controls:EmployeeListView DockPanel.Dock="Bottom" DataContext="{Binding EmployeeListViewModel}" />
This implies to me that your class structure is that MainViewModel contains an instance of the EmployeeListViewModel... is this true?
If all the above is true, then this part of your UserControl xaml does not make sense:
<DockPanel DataContext="{Binding MainViewModel,
RelativeSource={RelativeSource FindAncestor,
AncestorType={x:Type vm:EmployeeListViewModel}}}">
Whether EmployeeListViewModel is actually your view and not your viewmodel, the property "MainViewModel" does not exist on EmployeeListViewModel, so the binding will never work.
If you're trying to have a reference to your Window's DataContext, MainViewModel, within your UserControl, a possible way to do this is:
MainWindow.xaml:
<controls:EmployeeListView DockPanel.Dock="Bottom" DataContext="{Binding}" />
This should set the DataContext of your EmployeeListView to MainViewModel. Then, in your EmployeeListView, you can do this:
<UserControl x:Class="de.XXX.Views.EmployeeListView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:vm="clr-namespace:de.XXX.ViewModel"
xmlns:ia="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
mc:Ignorable="d"
d:DesignHeight="350" d:DesignWidth="350">
<DockPanel
<ListBox DockPanel.Dock="Bottom" x:Name="EmployeeList" ItemsSource="{Binding EmployeeList}" ScrollViewer.CanContentScroll="False" />
<ia:Interaction.Triggers>
<ia:EventTrigger EventName="Loaded">
<ia:InvokeCommandAction Command="{Binding EmployeeListViewModel.LoadEmployeesCommand}" />
</ia:EventTrigger>
</ia:Interaction.Triggers>
</DockPanel>
</UserControl>
There's a lot of assumptions about your views and viewmodels I made for this answer. I hope this at least helps. If it doesn't make any sense, please post your viewmodels as well :)