add relative panel page to control catalog.

samples/ControlCatalog/MainView.xaml

@@ -56,6 +56,7 @@
       <TabItem Header="Pointers (Touch)"><pages:PointersPage/></TabItem>
       <TabItem Header="ProgressBar"><pages:ProgressBarPage/></TabItem>
       <TabItem Header="RadioButton"><pages:RadioButtonPage/></TabItem>
+      <TabItem Header="RelativePanel"><pages:RelativePanelPage/></TabItem>
       <TabItem Header="ScrollViewer"><pages:ScrollViewerPage/></TabItem>
       <TabItem Header="Slider"><pages:SliderPage/></TabItem>
       <TabItem Header="SplitView"><pages:SplitViewPage/></TabItem>

samples/ControlCatalog/Pages/RelativePanelPage.axaml

@@ -0,0 +1,60 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+             x:Class="ControlCatalog.Pages.RelativePanelPage">
+    <RelativePanel Width="620" Height="700" Margin="32">
+        <Border Name="Rect1" Background="Red" Height="50" Width="50">
+            <TextBlock Text="Rect1" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect2" Background="Blue" Height="50" Width="50" RelativePanel.AlignHorizontalCenterWithPanel="True">
+            <TextBlock Text="Rect2" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect3" Background="Green" Height="50" Width="50" RelativePanel.AlignRightWithPanel="True">
+            <TextBlock Text="Rect3" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect4" Background="Red" Height="50" Width="50" RelativePanel.AlignBottomWithPanel="True">
+            <TextBlock Text="Rect4" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect5" Background="Blue" Height="50" Width="50" RelativePanel.AlignBottomWithPanel="True" RelativePanel.AlignHorizontalCenterWithPanel="True">
+            <TextBlock Text="Rect5" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect6" Background="Green" Height="50" Width="50" RelativePanel.AlignBottomWithPanel="True" RelativePanel.AlignRightWithPanel="True">
+            <TextBlock Text="Rect6" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect7" Background="Blue" Height="50" RelativePanel.RightOf="{Binding ElementName=Rect1}">
+            <TextBlock Text="Rect7 (RightOf Rect1)" Padding="10,0" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect8" Background="Green" Height="50" RelativePanel.Below="{Binding ElementName=Rect7}">
+            <TextBlock Text="Rect8 (Below Rect7)" Padding="10,0" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect9" Background="Blue" Height="140" Width="460" RelativePanel.AlignHorizontalCenterWithPanel="True" RelativePanel.AlignVerticalCenterWithPanel="True">
+            <TextBlock Text="Rect9" Padding="10" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Top"/>
+        </Border>
+        <Border Name="Rect10" Background="Red" Width="50" RelativePanel.RightOf="{Binding ElementName=Rect9}" RelativePanel.AlignVerticalCenterWith="{Binding ElementName=Rect9}">
+            <TextBlock Text="Rect14 (RightOf Rect9, AlignVerticalCenterWith Rect9)" Padding="10,0" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center">
+                <TextBlock.RenderTransform>
+                    <TransformGroup>
+                        <RotateTransform Angle="-90"/>
+                    </TransformGroup>
+                </TextBlock.RenderTransform>
+            </TextBlock>
+        </Border>
+        <Border Name="Rect11" Background="Red" Height="50" RelativePanel.AlignBottomWith="{Binding ElementName=Rect9}" RelativePanel.AlignHorizontalCenterWith="{Binding ElementName=Rect9}">
+            <TextBlock Text="Rect11 (AlignBottomWith Rect9, AlignHorizontalCenterWith Rect9)" Padding="10,0" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect12" Background="Red" Height="50" RelativePanel.Below="{Binding ElementName=Rect8}" RelativePanel.AlignLeftWith="{Binding ElementName=Rect7}">
+            <TextBlock Text="Rect12 (Below Rect8, AlignLeftWith Rect7)" Padding="10,0" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect13" Background="Blue" Height="50" RelativePanel.Below="{Binding ElementName=Rect12}" RelativePanel.AlignRightWith="{Binding ElementName=Rect12}">
+            <TextBlock Text="Rect13 (Below Rect12, AlignRightWith Rect12)" Padding="10,0" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect14" Background="Green" Height="50" RelativePanel.Above="{Binding ElementName=Rect9}" RelativePanel.AlignRightWith="{Binding ElementName=Rect9}">
+            <TextBlock Text="Rect14 (Above Rect9, AlignRightWith Rect9)" Padding="10,0" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+        <Border Name="Rect15" Background="Red" Height="50" RelativePanel.LeftOf="{Binding ElementName=Rect2}" RelativePanel.AlignTopWith="{Binding ElementName=Rect9}">
+            <TextBlock Text="Rect15 (LeftOf Rect2, AlignTopWith Rect9)" Padding="10,0" Foreground="White" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+        </Border>
+    </RelativePanel>
+</UserControl>

samples/ControlCatalog/Pages/RelativePanelPage.axaml.cs

@@ -0,0 +1,19 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace ControlCatalog.Pages
+{
+    public class RelativePanelPage : UserControl
+    {
+        public RelativePanelPage()
+        {
+            this.InitializeComponent();
+        }
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+    }
+}