Remove complex property from SwitchPresenter

Fix name of TargetType DependencyProperty
Add better Enum string support

Author: michael-hawker

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/Primitives/SwitchPresenter.bind

@@ -5,24 +5,28 @@
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
     xmlns:controls="using:Microsoft.Toolkit.Uwp.UI.Controls"
     xmlns:ui="using:Microsoft.Toolkit.Uwp.UI"
+    xmlns:enums="using:Microsoft.Toolkit.Uwp.SampleApp.Enums"
     mc:Ignorable="d">
 
   <StackPanel Padding="16">
+    <!-- Basic Sample -->
     <ComboBox x:Name="Lookup" Header="Look up reservation" SelectedIndex="0"
               Margin="0,0,0,8">
       <x:String>Select an option</x:String>
       <x:String>Confirmation Code</x:String>
       <x:String>E-ticket number</x:String>
       <x:String>Mileage Plan number</x:String>
     </ComboBox>
+    <!-- SwitchPresenter binds to a value -->
     <controls:SwitchPresenter Value="{Binding SelectedItem, ElementName=Lookup}">
+      <!-- And then only dynamically displays the Case with matching Value -->
       <controls:Case Value="Confirmation Code">
         <StackPanel>
           <TextBox Name="ConfirmationCodeValidator"
                    ui:TextBoxExtensions.Regex="^[a-zA-Z]{6}$"
                    Header="Confirmation code"
                    PlaceholderText="6 letters" />
-          <TextBlock Visibility="{Binding (ui:TextBoxExtensions.IsValid),ElementName=ConfirmationCodeValidator}">Thanks for entering a valid code!</TextBlock>
+          <TextBlock Visibility="{Binding (ui:TextBoxExtensions.IsValid), ElementName=ConfirmationCodeValidator}">Thanks for entering a valid code!</TextBlock>
         </StackPanel>
       </controls:Case>
       <controls:Case Value="E-ticket number">
@@ -31,7 +35,7 @@
                    ui:TextBoxExtensions.Regex="(^\d{10}$)|(^\d{13}$)"
                    Header="E-ticket number"
                    PlaceholderText="10 or 13 numbers" />
-          <TextBlock Visibility="{Binding (ui:TextBoxExtensions.IsValid),ElementName=TicketValidator}">Thanks for entering a valid code!</TextBlock>
+          <TextBlock Visibility="{Binding (ui:TextBoxExtensions.IsValid), ElementName=TicketValidator}">Thanks for entering a valid code!</TextBlock>
         </StackPanel>
       </controls:Case>
       <controls:Case Value="Mileage Plan number">
@@ -43,5 +47,23 @@
         <TextBlock>Please select a way to lookup your reservation above...</TextBlock>
       </controls:Case>
     </controls:SwitchPresenter>
+    
+    <!-- Advanced scenario using Type information -->
+    <ComboBox x:Name="AnimalPicker"
+              Header="Pick an Animal"
+              ItemsSource="{ui:EnumValues Type=enums:Animal}"
+              SelectedIndex="0"/>
+    <controls:SwitchPresenter Value="{Binding SelectedItem, ElementName=AnimalPicker}"
+                              TargetType="enums:Animal">
+      <controls:Case Value="Cat">
+        <TextBlock>🐈</TextBlock>
+      </controls:Case>
+      <controls:Case Value="Dog">
+        <TextBlock>🐕</TextBlock>
+      </controls:Case>
+      <controls:Case Value="Bunny">
+        <TextBlock>🐇</TextBlock>
+      </controls:Case>
+    </controls:SwitchPresenter>
   </StackPanel>
 </Page>

Microsoft.Toolkit.Uwp.UI.Controls.Primitives/SwitchPresenter/SwitchPresenter.cs

@@ -68,25 +68,16 @@ public object Value
         /// </summary>
         public Type TargetType
         {
-            get { return (Type)GetValue(DataTypeProperty); }
-            set { SetValue(DataTypeProperty, value); }
+            get { return (Type)GetValue(TargetTypeProperty); }
+            set { SetValue(TargetTypeProperty, value); }
         }
 
         /// <summary>
         /// Indicates the <see cref="TargetType"/> property.
         /// </summary>
-        public static readonly DependencyProperty DataTypeProperty =
+        public static readonly DependencyProperty TargetTypeProperty =
             DependencyProperty.Register(nameof(TargetType), typeof(Type), typeof(SwitchPresenter), new PropertyMetadata(null));
 
-        /// <summary>
-        /// Gets or sets a value indicating whether the content is removed from the visual tree when
-        /// switching between cases. This calls <see cref="VisualTreeHelper.DisconnectChildrenRecursive(UIElement)"/>
-        /// when switching between cases, so is only meant if the displayed case is never intended to be
-        /// shown again. No explicit re-initialization of controls is provided by the <see cref="SwitchPresenter"/>.
-        /// </summary>
-        [EditorBrowsable(EditorBrowsableState.Never)]
-        public bool IsVisualTreeDisconnectedOnChange { get; set; }
-
         private static void OnSwitchCasesPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
         {
             if (e.OldValue != null)
@@ -175,33 +166,12 @@ private void EvaluateCases()
                 newcase = xdefault;
             }
 
-            // Only bother changing things around if we have a new case.
+            // Only bother changing things around if we actually have a new case.
             if (newcase != CurrentCase)
             {
-                // Disconnect old content from visual tree.
-                if (CurrentCase != null && CurrentCase.Content != null && IsVisualTreeDisconnectedOnChange)
-                {
-                    // When we disconnect here, we can't easily redo anything done here, so this is
-                    // an advanced option left open to specific scenarios for a developer.
-                    // It shouldn't come up in normaly usages, unless a developer intends each
-                    // case to only be displayed once.
-                    VisualTreeHelper.DisconnectChildrenRecursive(CurrentCase.Content);
-                }
-
-                // We don't have any cases or a default to go to, so go back to blank
-                if (newcase == null)
-                {
-                    Content = null;
-
-                    CurrentCase = null;
-                }
-                else
-                {
-                    // Hookup new content.
-                    Content = newcase.Content;
-
-                    CurrentCase = newcase;
-                }
+                // If we don't have any cases or default, setting these to null is what we want to be blank again.
+                Content = newcase?.Content;
+                CurrentCase = newcase;
             }
         }
 
@@ -255,6 +225,20 @@ internal static object ConvertValue(Type targetType, object value)
             {
                 return value;
             }
+            else if (targetType.IsEnum && value is string str)
+            {
+                if (Enum.TryParse(targetType, str, out object result))
+                {
+                    return result;
+                }
+
+                static object ThrowExceptionForKeyNotFound()
+                {
+                    throw new InvalidOperationException("The requested enum value was not present in the provided type.");
+                }
+
+                return ThrowExceptionForKeyNotFound();
+            }
             else
             {
                 return XamlBindingHelper.ConvertValue(targetType, value);