Question

I would like to know if this is a standard feature of .NET: when setting the DataContext in the ParentView, it filters down to all child views.

Say you have ParentView, ChildView1 and ChildView2:

<UserControl x:Class="DXWPFApplication1.ParentView"
             xmlns:view="clr-namespace:DXWPFApplication1"
             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" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <view:ChildView1  x:Name="childView1"/>
    </Grid>
</UserControl>

<UserControl x:Class="DXWPFApplication1.ChildView1"
             xmlns:view="clr-namespace:DXWPFApplication1"
             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" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <view:ChildView2  x:Name="childView2"/>
    </Grid>
</UserControl>

Code behind of ParentView:

public ParentView() 
        {
            InitializeComponent();

            DataContext = "ViewModel"; //BreakPoint here

            //
            //When the first DataContext is set, all the DataContext's below are set as well
            //

            childView1.DataContext = DataContext;
            childView1.childView2.DataContext = DataContext;
        }

NOTE: Breakpoint when setting first DataContext

Why are all the DataContexts set when I have only set the ParentView’s DataContext?

What can I do to prevent this from happening?

Answer 1

This is standard behaviour, and normally desired. To prevent it, set DataContext to {x:Null} in your markup