Pull TranslatePoint() calculation into dedicated AP (#3699)

Author: nicolaihenriksen

src/MaterialDesignThemes.Wpf/Behaviors/SmartHintBehavior.cs

@@ -0,0 +1,39 @@
+using Microsoft.Xaml.Behaviors;
+
+namespace MaterialDesignThemes.Wpf.Behaviors;
+
+public class SmartHintBehavior : Behavior<SmartHint>
+{
+    public static readonly DependencyProperty YOffsetProperty =
+        DependencyProperty.RegisterAttached("YOffset", typeof(double), typeof(SmartHintBehavior), new PropertyMetadata(0.0));
+    public static double GetYOffset(DependencyObject obj)
+        => (double)obj.GetValue(YOffsetProperty);
+    public static void SetYOffset(DependencyObject obj, double value)
+        => obj.SetValue(YOffsetProperty, value);
+
+    private void UpdateSmartHintLocationRecalculationTrigger()
+    {
+        if (AssociatedObject?.FloatingTarget is null) return;
+
+        double yOffset = AssociatedObject.FloatingTarget.TranslatePoint(new Point(0, 0), AssociatedObject).Y;
+        AssociatedObject.SetCurrentValue(YOffsetProperty, yOffset);
+    }
+
+    private void HintHostOnLayoutUpdated(object? sender, EventArgs e)
+        => UpdateSmartHintLocationRecalculationTrigger();
+
+    protected override void OnAttached()
+    {
+        base.OnAttached();
+        AssociatedObject.LayoutUpdated += HintHostOnLayoutUpdated;
+    }
+
+    protected override void OnDetaching()
+    {
+        if (AssociatedObject != null)
+        {
+            AssociatedObject.LayoutUpdated -= HintHostOnLayoutUpdated;
+        }
+        base.OnDetaching();
+    }
+}

src/MaterialDesignThemes.Wpf/Converters/FloatingHintTranslateTransformConverter.cs

@@ -1,4 +1,4 @@
-using System.Globalization;
+using System.Globalization;
 using System.Windows.Data;
 using System.Windows.Media;
 
@@ -8,7 +8,7 @@ public class FloatingHintTranslateTransformConverter : IMultiValueConverter
 {
     public object? Convert(object?[]? values, Type targetType, object? parameter, CultureInfo culture)
     {
-        if (values is not [double scale, double lower, double upper, SmartHint hint, Point floatingOffset, ..])
+        if (values is not [double scale, double lower, double upper, SmartHint hint, Point floatingOffset, double yOffset, ..])
         {
             return Transform.Identity;
         }
@@ -43,7 +43,7 @@ double GetFloatingTargetHorizontalOffset()
 
         double GetFloatingTargetVerticalOffset()
         {
-            double offset = hint.FloatingTarget.TranslatePoint(new Point(0, 0), hint).Y;
+            double offset = yOffset;
             offset += hint.InitialVerticalOffset;
             offset -= hint.ActualHeight;
 

src/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.SmartHint.xaml

@@ -2,7 +2,8 @@
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:converters="clr-namespace:MaterialDesignThemes.Wpf.Converters"
                     xmlns:system="clr-namespace:System;assembly=mscorlib"
-                    xmlns:wpf="clr-namespace:MaterialDesignThemes.Wpf">
+                    xmlns:wpf="clr-namespace:MaterialDesignThemes.Wpf"
+                    xmlns:behaviors="clr-namespace:MaterialDesignThemes.Wpf.Behaviors">
 
   <Style TargetType="{x:Type wpf:SmartHint}">
     <Style.Resources>
@@ -18,6 +19,13 @@
       <converters:FloatingHintTextBlockMarginConverter x:Key="FloatingHintTextBlockMarginConverter" />
       <converters:FloatingHintClippingGridConverter x:Key="FloatingHintClippingGridConverter" />
     </Style.Resources>
+    <Setter Property="wpf:BehaviorsAssist.Behaviors">
+      <Setter.Value>
+        <wpf:BehaviorCollection>
+          <behaviors:SmartHintBehavior />
+        </wpf:BehaviorCollection>
+      </Setter.Value>
+    </Setter>
     <Setter Property="HorizontalAlignment" Value="Stretch" />
     <Setter Property="HorizontalContentAlignment" Value="Left" />
     <Setter Property="IsHitTestVisible" Value="False" />
@@ -158,6 +166,7 @@
                       <Binding Source="{StaticResource NoContentFloatingScale}" />
                       <Binding Path="." RelativeSource="{RelativeSource TemplatedParent}" />
                       <Binding Path="FloatingOffset" RelativeSource="{RelativeSource TemplatedParent}" />
+                      <Binding Path="(behaviors:SmartHintBehavior.YOffset)" RelativeSource="{RelativeSource TemplatedParent}" />
                       <!-- The bindings below are only here to trigger a recalculation - needed to support AcceptsReturn=true scenario for TextBoxes for example as well as "runtime" changes to the desired hint placement -->
                       <Binding Path="InitialVerticalOffset" RelativeSource="{RelativeSource TemplatedParent}" />
                       <Binding Path="InitialHorizontalOffset" RelativeSource="{RelativeSource TemplatedParent}" />