Accesing properties in a UserControl from the MainWindow (WPF/MVVM)

Question

I have a little problem and I'm looking the correct way to implement it.

I have a MainWindow and a UserControl to display some result, in the MainWindow I have a button "load" to load some data and the UserControl should display them.

I'm not sure what is the correct way to do this in WPF and MVVM:

Should I pass the MainWindowModel to the UserControlModel?;

Should I pass the UserControlModel to the MainWindowModel?;

Should I expose the property I need to fill as DependencyProperty in my UserControl and then fill it on the MainWindow?

Any suggestion would be appreciated. Thanks!

Edit 1: This is how I call my UserControl:

<TabControl Grid.Row="1"
            Grid.RowSpan="2"
            Grid.Column="0"
            VerticalAlignment="Stretch">

    <!--Result View-->
    <TabItem Header="{Binding TabImportHeader}">
        <results:ResultView/>
    </TabItem>

    <!--Configuration Tab-->
    <TabItem Header="{Binding TabConfigurationHeader}">
        <configuration:ConfigurationView />
    </TabItem>
</TabControl>

My UserControl where my problem appear is the ResultView

Answer 1

MainWindowVMInstance.UserControlVMInstance.Property

The UserControl is inside your MainWindow.

Therefore your MainWindow has a property (/instance) of your UserControlVM.

Note: If you also need a reference of MainWindowVM inside your UserControlVM, pass it to the constructor and store it as property.

In xaml it would look like this (inside MainWindow.xaml):

<ContentControl Content="{Binding UserControlVMInstance}"/>

Don't forget the DataTemplate:

<DataTemplate DataType="{x:Type vm:UserControlVM}">
    <view:UserControlView/>
</DataTemplate>

---

Edit after question update:

This is an example with a part of your code to demonstrate WPF and MVVM in action. You simply define a DataTemplate in your UserControl.Resources and then give the ContentControl via Binding an instance of your UserControlVM. WPF knows there's a DataTemplate for this type and will add an instance of the UserControlView where the ContentControl is.

<MainWindow>
    <MainWindow.Resources>
        <DataTemplate DataType="{x:Type vm:UserControlVM}">
            <view:UserControlView/>
        </DataTemplate>
    </MainWindow.Resources>

    <!-- Your TabControl -->
    <TabControl>
        <!--Result View-->
        <TabItem Header="{Binding TabImportHeader}">
            <ContentControl Content="{Binding TabImportCONTENT}"/>
        </TabItem>
    </TabControl>
</MainWindow>