update the test app to show the size that measure was called with on window content.

samples/IntegrationTestApp/ShowWindowTest.axaml

@@ -1,41 +1,50 @@
 <Window xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:integrationTestApp="clr-namespace:IntegrationTestApp"
         x:Class="IntegrationTestApp.ShowWindowTest"
         Name="SecondaryWindow"
         x:DataType="Window"
         Title="Show Window Test">
-  <Grid ColumnDefinitions="Auto,Auto" RowDefinitions="Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto">
-    <Label Grid.Column="0" Grid.Row="1">Client Size</Label>
-    <TextBox Name="ClientSize" Grid.Column="1" Grid.Row="1" IsReadOnly="True"
-             Text="{Binding ClientSize, Mode=OneWay}"/>
-    
-    <Label Grid.Column="0" Grid.Row="2">Frame Size</Label>
-    <TextBox Name="FrameSize" Grid.Column="1" Grid.Row="2" IsReadOnly="True"
-             Text="{Binding FrameSize, Mode=OneWay}"/>
-
-    <Label Grid.Column="0" Grid.Row="3">Position</Label>
-    <TextBox Name="Position" Grid.Column="1" Grid.Row="3" IsReadOnly="True"/>
-
-    <Label Grid.Column="0" Grid.Row="4">Owner Rect</Label>
-    <TextBox Name="OwnerRect" Grid.Column="1" Grid.Row="4" IsReadOnly="True"/>
-    
-    <Label Grid.Column="0" Grid.Row="5">Screen Rect</Label>
-    <TextBox Name="ScreenRect" Grid.Column="1" Grid.Row="5" IsReadOnly="True"/>
-
-    <Label Grid.Column="0" Grid.Row="6">Scaling</Label>
-    <TextBox Name="Scaling" Grid.Column="1" Grid.Row="6" IsReadOnly="True"/>
-    
-    <Label Grid.Column="0" Grid.Row="7">WindowState</Label>
-    <ComboBox Name="WindowState" Grid.Column="1" Grid.Row="7" SelectedIndex="{Binding WindowState}">
-      <ComboBoxItem Name="WindowStateNormal">Normal</ComboBoxItem>
-      <ComboBoxItem Name="WindowStateMinimized">Minimized</ComboBoxItem>
-      <ComboBoxItem Name="WindowStateMaximized">Maximized</ComboBoxItem>
-      <ComboBoxItem Name="WindowStateFullScreen">FullScreen</ComboBoxItem>
-    </ComboBox>
-
-    <Label Grid.Column="0" Grid.Row="8">Order (mac)</Label>
-    <TextBox Name="Order" Grid.Column="1" Grid.Row="8" IsReadOnly="True"/>
-
-    <Button Name="HideButton" Grid.Row="9" Command="{Binding $parent[Window].Hide}">Hide</Button>
-  </Grid>
+  <integrationTestApp:MeasureBorder Name="MyBorder">
+    <Grid ColumnDefinitions="Auto,Auto" RowDefinitions="Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto">
+      <Label Grid.Column="0" Grid.Row="1">Client Size</Label>
+      <TextBox Name="ClientSize" Grid.Column="1" Grid.Row="1" IsReadOnly="True"
+               Text="{Binding ClientSize, Mode=OneWay}" />
+
+      <Label Grid.Column="0" Grid.Row="2">Frame Size</Label>
+      <TextBox Name="FrameSize" Grid.Column="1" Grid.Row="2" IsReadOnly="True"
+               Text="{Binding FrameSize, Mode=OneWay}" />
+
+      <Label Grid.Column="0" Grid.Row="3">Position</Label>
+      <TextBox Name="Position" Grid.Column="1" Grid.Row="3" IsReadOnly="True" />
+
+      <Label Grid.Column="0" Grid.Row="4">Owner Rect</Label>
+      <TextBox Name="OwnerRect" Grid.Column="1" Grid.Row="4" IsReadOnly="True" />
+
+      <Label Grid.Column="0" Grid.Row="5">Screen Rect</Label>
+      <TextBox Name="ScreenRect" Grid.Column="1" Grid.Row="5" IsReadOnly="True" />
+
+      <Label Grid.Column="0" Grid.Row="6">Scaling</Label>
+      <TextBox Name="Scaling" Grid.Column="1" Grid.Row="6" IsReadOnly="True" />
+
+      <Label Grid.Column="0" Grid.Row="7">WindowState</Label>
+      <ComboBox Name="WindowState" Grid.Column="1" Grid.Row="7" SelectedIndex="{Binding WindowState}">
+        <ComboBoxItem Name="WindowStateNormal">Normal</ComboBoxItem>
+        <ComboBoxItem Name="WindowStateMinimized">Minimized</ComboBoxItem>
+        <ComboBoxItem Name="WindowStateMaximized">Maximized</ComboBoxItem>
+        <ComboBoxItem Name="WindowStateFullScreen">FullScreen</ComboBoxItem>
+      </ComboBox>
+
+      <Label Grid.Column="0" Grid.Row="8">Order (mac)</Label>
+      <TextBox Name="Order" Grid.Column="1" Grid.Row="8" IsReadOnly="True" />
+
+      <Button Name="HideButton" Grid.Row="9" Command="{Binding $parent[Window].Hide}">Hide</Button>
+      
+      <StackPanel Grid.Row="10" Orientation="Horizontal">
+        <TextBlock Text="MeasuredWith:" />
+        <TextBlock Name="MeasuredWithText" Text="{Binding #MyBorder.MeasuredWith}" />
+      </StackPanel>
+      
+    </Grid>
+  </integrationTestApp:MeasureBorder>
 </Window>

samples/IntegrationTestApp/ShowWindowTest.axaml.cs

@@ -7,6 +7,25 @@ using Avalonia.Threading;
 
 namespace IntegrationTestApp
 {
+    public class MeasureBorder : Border
+    {
+        protected override Size MeasureOverride(Size availableSize)
+        {
+            MeasuredWith = availableSize;
+            
+            return base.MeasureOverride(availableSize);
+        }
+
+        public static readonly StyledProperty<Size> MeasuredWithProperty = AvaloniaProperty.Register<MeasureBorder, Size>(
+            nameof(MeasuredWith));
+
+        public Size MeasuredWith
+        {
+            get => GetValue(MeasuredWithProperty);
+            set => SetValue(MeasuredWithProperty, value);
+        }
+    }
+    
     public class ShowWindowTest : Window
     {
         private readonly DispatcherTimer? _timer;