Problem adding a UserControl in a TabItem

I tried adding a UserControl to a TabItem in the following way:

<TabControl Margin="1">
        <TabItem Header="Control" >
        </TabItem>
        <TabItem Header="Tray" >
            <local:SettingView>
            </local:SettingView>
        </TabItem>
</T开发者_如何学CabControl>

It showed in the UI, but bindings appear to be evaluated while the DataContext of the UserControl is still null (Nothing). Why isn't this working?