In the following example SelectedValue of TabControl is always null. Why?

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib">
<DockPanel>
    <TextBlock Text="{Binding SelectedValue, ElementName=Tabs}" DockPanel.Dock="Bottom"/>
    <TabControl x:Name="Tabs" SelectedValuePath="Content.SelectedItem">
        <TabItem Header="TabOne">
            <ListView>
                <ListView.View>
                    <GridView>
                        <GridViewColumn/>
                    </GridView>
                </ListView.View>
                <s:String>ItemOne</s:String>
                <s:String>ItemTwo</s:String>
            </ListView>
        </TabItem>
        <TabItem Header="TabTwo">
            <ListView>
                <ListView.View>
                    <GridView>
                        <GridViewColumn/>
                    </GridView>
                </ListView.View>
                <s:String>ItemOne</s:String>
                <s:String>ItemTwo</s:String>
            </ListView>
        </TabItem>
    </TabControl>
</DockPanel>
</Window>

• wpf
• xaml
• selectedvalue

As micahtan points out in a comment, SelectedValue does update when you switch tabs. This means that TabControl does not monitor properties in SelectedValuePath for changes, only polls them every time its SelectedItem changes.

Not sure what your trying to do, but:

Assuming that you want the name of the selected TabItem to show up in the TextBlock, it's because your SelectedValuePath is incorrect. Try changing your TabControl tag to:

<TabControl x:Name="Tabs" SelectedValuePath="Header">

Assuming that you're trying to get the string contents inside of the ListView, try changing your TextBox binding to:

<TextBlock Text="{Binding SelectedItem.Content.SelectedItem, ElementName=Tabs}" DockPanel.Dock="Bottom"/>