MainWindow.xaml

<Window x:Class="dependencyinjection.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:dependencyinjection"
        xmlns:DependencyInjection="clr-namespace:dependencyinjection.ViewModels.DependencyInjection"
        xmlns:Nulltovisconverter="clr-namespace:nulltovisconverter;assembly=nulltovisconverter"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525"
        d:DataContext="{d:DesignInstance DependencyInjection:FooViewModel}">
    <Grid>
        <TextBlock Text="FooViewModel is DataContext and BarViewModel is injected into it" Visibility="{Binding 
        BarViewModel, Converter={Nulltovisconverter:NullToVisibilityConverter Inverted=True}}"/>
    </Grid>
</Window>