What is "[Xamarin.Forms.ContentProperty("Contents")]" above a class actually doing?

Issue

I understand how this code works but can someone explain what the first line does? Is this translated some place into some C# code. How about if I wanted to code this manually, how could I go about that?

[Xamarin.Forms.ContentProperty("Contents")]
class PopupFrame : Frame
{
    StackLayout contentStack { get; } = new StackLayout();

    public IList<View> Contents { get => contentStack.Children; }


    public PopupFrame()
    {
        Content = contentStack;

        HasShadow = true;
        HorizontalOptions = LayoutOptions.FillAndExpand;
        Padding = 0;
        VerticalOptions = LayoutOptions.Center;
    }
}

Solution

This attribute tells the XAML processor that if should use the Frame's Content property as the default basically. So, in practice it allows you to write this

<ContentView>
    <Label Text="Hello, Forms"/>
</ContentView>

Instead of

<ContentView>
    <ContentView.Content>
       <Label Text="Hello, Forms"/>
    </ContentView.Content>
</ContentView>

Examples taken from the Docs page.

In regard to your question "how do I write this in C#?" you don't. This is something specific to XAML and nothing more than syntactic sugar. In C# you would simply assign something to the Content property. I.e.:

var frame = new Frame();

Frame.Content = new Label() { Text = "Hello, Forms" };

Answered By - Gerald Versluis