What does it mean then to declare nested xaml elements inside our simple class then?

e.g.

<custom :SimpleBase x:Class="TestType"
                    xmlns:custom="clr-namespace:ConsoleApplication1;assembly="
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
Test
</custom>

Well, if you try it you will find this isn’t possible. And indeed I also can’t figure out what it might mean. And yet if you open any book on XAML you will find things like <button>Click Me</button>. Hmm.

The answer lies in the definition of the base type (in our case SimpleBase).

In order to be able to assign direct content such as this we must declare a property on the base type and add a [System.Windows.Markup.ContentProperty(“…”)] attribute to it where the … is replaced with the name of the property that should take the content.

    [System.Windows.Markup.ContentProperty("PropertyOne")]
    public class SimpleBase
    {
        public string PropertyOne { get; set; }
        public string PropertyTwo { get; set; }
    }

Now in xaml we can assign the value PropertyOne using the following syntax:

<custom :SimpleBase x:Class="TestType"
                    xmlns:custom="clr-namespace:ConsoleApplication1;assembly="
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:sys="clr-namespace:System;assembly=mscorlib">
    <sys :String>Test</sys>
</custom>

Interestingly it still isn’t possible to directly enter the string ‘Test’, only to assign a sys:String object containing Test. Putting Test directly in the xml leads to a compile error.