Add PreviousVersionInstalled to sample app

Update doc in app sample
Fix XML property comment

Author: Panda-Sharp

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/SystemInformation/SystemInformationCode.bind

@@ -37,6 +37,9 @@
         // To get the first version installed
         public PackageVersion FirstVersionInstalled => SystemInformation.Instance.FirstVersionInstalled;
 
+        // To get the previous version installed
+        public string PreviousVersionInstalled => SystemInformation.Instance.PreviousVersionInstalled.ToFormattedString();
+
         // To get the first time the app was launched
         public DateTime FirstUseTime => SystemInformation.Instance.FirstUseTime;
 

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/SystemInformation/SystemInformationPage.xaml

@@ -170,6 +170,18 @@
                 <StackPanel x:Name="Stack13"
                             Margin="10"
                             Orientation="Horizontal">
+                    <TextBlock FontSize="18"
+                               FontWeight="Bold"
+                               Text="Previous version installed:"
+                               TextWrapping="Wrap" />
+                    <TextBlock Margin="20,0"
+                               FontSize="18"
+                               Text="{x:Bind PreviousVersionInstalled}"
+                               TextWrapping="Wrap" />
+                </StackPanel>
+                <StackPanel x:Name="Stack14"
+                            Margin="10"
+                            Orientation="Horizontal">
                     <TextBlock FontSize="18"
                                FontWeight="Bold"
                                Text="First use time:"
@@ -179,7 +191,7 @@
                                Text="{x:Bind FirstUseTime}"
                                TextWrapping="Wrap" />
                 </StackPanel>
-                <StackPanel x:Name="Stack14"
+                <StackPanel x:Name="Stack15"
                             Margin="10"
                             Orientation="Horizontal">
                     <TextBlock FontSize="18"
@@ -191,7 +203,7 @@
                                Text="{x:Bind LaunchTime}"
                                TextWrapping="Wrap" />
                 </StackPanel>
-                <StackPanel x:Name="Stack15"
+                <StackPanel x:Name="Stack16"
                             Margin="10"
                             Orientation="Horizontal">
                     <TextBlock FontSize="18"
@@ -203,7 +215,7 @@
                                Text="{x:Bind LastLaunchTime}"
                                TextWrapping="Wrap" />
                 </StackPanel>
-                <StackPanel x:Name="Stack16"
+                <StackPanel x:Name="Stack17"
                             Margin="10"
                             Orientation="Horizontal">
                     <TextBlock FontSize="18"
@@ -215,7 +227,7 @@
                                Text="{x:Bind LastResetTime, Mode=OneWay}"
                                TextWrapping="Wrap" />
                 </StackPanel>
-                <StackPanel x:Name="Stack17"
+                <StackPanel x:Name="Stack18"
                             Margin="10"
                             Orientation="Horizontal">
                     <TextBlock FontSize="18"
@@ -227,7 +239,7 @@
                                Text="{x:Bind LaunchCount, Mode=OneWay}"
                                TextWrapping="Wrap" />
                 </StackPanel>
-                <StackPanel x:Name="Stack18"
+                <StackPanel x:Name="Stack19"
                             Margin="10"
                             Orientation="Horizontal">
                     <TextBlock FontSize="18"
@@ -239,7 +251,7 @@
                                Text="{x:Bind TotalLaunchCount}"
                                TextWrapping="Wrap" />
                 </StackPanel>
-                <StackPanel x:Name="Stack19"
+                <StackPanel x:Name="Stack20"
                             Margin="10"
                             Orientation="Horizontal">
                     <TextBlock FontSize="18"
@@ -284,6 +296,9 @@
                         <Setter Target="Stack15.Orientation" Value="Vertical" />
                         <Setter Target="Stack16.Orientation" Value="Vertical" />
                         <Setter Target="Stack17.Orientation" Value="Vertical" />
+                        <Setter Target="Stack18.Orientation" Value="Vertical" />
+                        <Setter Target="Stack19.Orientation" Value="Vertical" />
+                        <Setter Target="Stack20.Orientation" Value="Vertical" />
                     </VisualState.Setters>
                 </VisualState>
             </VisualStateGroup>

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/SystemInformation/SystemInformationPage.xaml.cs

@@ -54,6 +54,9 @@ public sealed partial class SystemInformationPage : Page
         // To get the first version installed
         public string FirstVersionInstalled => SystemInformation.Instance.FirstVersionInstalled.ToFormattedString();
 
+        // To get the previous version installed
+        public string PreviousVersionInstalled => SystemInformation.Instance.PreviousVersionInstalled.ToFormattedString();
+
         // To get the first time the app was launched
         public string FirstUseTime => SystemInformation.Instance.FirstUseTime.ToString(Culture.DateTimeFormat);
 

Microsoft.Toolkit.Uwp/Helpers/SystemInformation.cs

@@ -123,7 +123,8 @@ public static async Task LaunchStoreForReviewAsync()
 
         /// <summary>
         /// Gets the previous version of the app that was installed.
-        /// This will be the current version if a previous version of the app was installed before accessing this property.
+        /// This will be the current version if a previous version of the app was installed
+        /// before using SystemInformation or if the app is not updated.
         /// </summary>
         public PackageVersion PreviousVersionInstalled { get; }
 
@@ -346,6 +347,7 @@ private bool DetectIfAppUpdated()
                 var lastVersion = _localObjectStorageHelper.Read<string>(nameof(currentVersion));
                 if (currentVersion != lastVersion)
                 {
+                    _localObjectStorageHelper.Save(nameof(PreviousVersionInstalled), lastVersion);
                     _localObjectStorageHelper.Save(nameof(currentVersion), currentVersion);
                     return true;
                 }