How to use a ContentPresenter inside a UserControl

Use the ContentPropertyAttribute to instruct the xaml to set this property instead of the actual Content property.

[ContentProperty("InnerContent")]public partial class ModernButton : UserControl{    public ModernButton()    {        InitializeComponent();    }    public static readonly DependencyProperty InnerContentProperty =        DependencyProperty.Register("InnerContent", typeof(object), typeof(ModernButton));    public object InnerContent    {        get { return (object)GetValue(InnerContentProperty); }        set { SetValue(InnerContentProperty, value); }    }}

Then in your xaml, Bind the Content Presenter to use InnerContent property instead.

<ContentPresenter Content="{Binding InnerContent, ElementName=_modernButton}"/>

This way you can do the following without replacing the actual content.

<control:ModernButton Size="200" BackgroundColor="Light">    TEST</control:ModernButton>

Here we go.

<UserControl x:Class="SGDB.UI.Controls.ModernButton"     xmlns:local="clr-namespace:SGDB.UI.Controls"     xmlns:converter="clr-namespace:SGDB.UI.Converter"     x:Name="_modernButton">    <UserControl.Template>        <ControlTemplate TargetType="UserControl">            <Button Content="{TemplateBinding Content}">                 <Button.Resources>                    <converter:EnumToColorConverter x:Key="ColorConverter"/>                  </Button.Resources>            <Button.Template >                <ControlTemplate TargetType="Button">                    <Border Width="{Binding Size,                                    ElementName=_modernButton}"                    Height="{Binding Size,                                     ElementName=_modernButton}"                    BorderBrush="Black"                    BorderThickness="0.8,0.8,3,3">                        <Grid Background="{Binding BackgroundColor, ElementName=_modernButton, Converter={StaticResource ColorConverter}}">                            <ContentPresenter />                        </Grid>                    </Border>                </ControlTemplate>            </Button.Template>            </Button>        </ControlTemplate>    </UserControl.Template></UserControl>

Let's assume that youre UserControl is:

<UserControl x:Class="QuickAndDirtyAttempt.Decorator" ....      <UserControl.Template>        <ControlTemplate TargetType="{x:Type local:Decorator}">          <StackPanel Orientation="Vertical">            <Label>Foo</Label>            <ContentPresenter/>            <Label>Bar</Label>          </StackPanel>        </ControlTemplate>      </UserControl.Template></UserControl>

Note the TargetType property on the template: without it the project will happily compile, but the ContentPresenter will not work.And then:

<Window ... >    <StackPanel Orientation="Vertical">        <local:Decorator>            <Label Background="Wheat">User supplied content here</Label>        </local:Decorator>    </StackPanel></Window> 

I strongly recommend you to read this before implementing anything