Xamarin TemplateControl 相对源绑定

Question

Currently there is an issue with Xamarin Shell navigation that causes the destination page's content to be hidden underneath the navigation bar at the top of the page. I am trying to make a control template to wrap the content in a container with a sufficient top-margin to shove the content down the screen, out from under the nav bar. Following the guidance here , what I have currently --

<?xml version="1.0" encoding="utf-8" ?>
<Application xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"
             x:Class="Y12.Mobile.MovePlan.App">
    <Application.Resources>
        <ResourceDictionary>
            <ControlTemplate x:Key="NavBarContentControlTemplate">
                <StackLayout
                    BindingContext="{Binding Source={RelativeSource TemplatedParent}}"
                    Margin="0, 50, 0, 0">
                    <Label Text="Hello Template!"></Label>
                    <ContentView Content="{Binding Content}"></ContentView>
                </StackLayout>
            </ControlTemplate>
        </ResourceDictionary>
    </Application.Resources>
</Application>

-- doesn't seem to work. I get an Intellisense highlight at {RelativeSource TemplatedParent} , with the following error XLS0414:

The type 'RelativeSource' was not found. Verify that you are not missing an assembly reference and that all referenced assemblies have been built.

What do I need to do to set the BindingContext properly here?

Answer 1

Looks like I needed to read further down the page. Later it has a section describing how to Pass parameters with TemplateBinding where it states,

The TemplateBinding markup extension is an alternative to creating a ControlTemplate that uses the RelativeSource markup extension to set the BindingContext of the root element in the template to its templated parent. The TemplateBinding markup extension eliminates the RelativeSource binding, and replaces the Binding expressions with TemplateBinding expressions.

And further,

Using the TemplateBinding markup extension is equivalent to setting the BindingContext of the root element in the template to its templated parent with the RelativeSource markup extension, and then resolving bindings of child objects with the Binding markup extension. In fact, the TemplateBinding markup extension creates a Binding whose Source is RelativeBindingSource.TemplatedParent.

Applying this, I was able to change the above code to the following:

<?xml version="1.0" encoding="utf-8" ?>
<Application xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"
             x:Class="Y12.Mobile.MovePlan.App">
    <Application.Resources>
        <ResourceDictionary>
            <ControlTemplate x:Key="NavBarContentControlTemplate">
                <StackLayout
                    Margin="0, 50, 0, 0">
                    <Label Text="Hello Template!"></Label>
                    <ContentView Content="{TemplateBinding Content}"></ContentView>
                </StackLayout>
            </ControlTemplate>
        </ResourceDictionary>
    </Application.Resources>
</Application>

And it works just fine.