TemplatePart XAML diagnostics

.editorconfig

@@ -212,6 +212,12 @@ indent_size = 2
 avalonia_xaml_diagnostic.AVLN2203.severity = error
 # StyleInMergedDictionaries
 avalonia_xaml_diagnostic.AVLN2204.severity = error
+# RequiredTemplatePartMissing
+avalonia_xaml_diagnostic.AVLN2205.severity = error
+# OptionalTemplatePartMissing
+avalonia_xaml_diagnostic.AVLN2206.severity = info
+# TemplatePartWrongType
+avalonia_xaml_diagnostic.AVLN2207.severity = error
 # Obsolete
 avalonia_xaml_diagnostic.AVLN5001.severity = error
 

samples/ControlCatalog/Pages/TransitioningContentControlPage.axaml

@@ -23,10 +23,12 @@
                                 <ColumnDefinition Width="Auto" SharedSizeGroup="HeaderCol" />
                                 <ColumnDefinition Width="*" />
                             </Grid.ColumnDefinitions>
-                            <ContentPresenter Content="{TemplateBinding Header}" 
+                            <ContentPresenter x:Name="PART_HeaderPresenter"
+                                              Content="{TemplateBinding Header}" 
                                               Grid.Column="0" 
                                               VerticalAlignment="Center" />
-                            <ContentPresenter Content="{TemplateBinding Content}" 
+                            <ContentPresenter x:Name="PART_ContentPresenter"
+                                              Content="{TemplateBinding Content}" 
                                               Grid.Column="1" 
                                               VerticalAlignment="Center" />
                         </Grid>

src/Avalonia.Base/Controls/Metadata/TemplatePartAttribute.cs

@@ -5,8 +5,6 @@
 
 using System;
 
-#nullable enable
-
 namespace Avalonia.Controls.Metadata
 {
     /// <summary>
@@ -17,7 +15,7 @@ namespace Avalonia.Controls.Metadata
     /// Style authors should be able to identify the part type used for styling the specific control.
     /// The part is usually required in the style and should have a specific predefined name.
     /// </remarks>
-    [AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
+    [AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = true)]
     public sealed class TemplatePartAttribute : Attribute
     {
         /// <summary>
@@ -51,5 +49,10 @@ public TemplatePartAttribute(string name, Type type)
         /// in <see cref="Name"/>.
         /// </summary>
         public Type Type { get; set; }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether the template part is mandatory to be present in the template.
+        /// </summary>
+        public bool IsRequired { get; set; }
     }
 }

src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml

@@ -183,7 +183,8 @@
                     <ColumnDefinition Width="Auto" MinWidth="{DynamicResource DataGridSortIconMinWidth}" />
                   </Grid.ColumnDefinitions>
 
-                  <ContentPresenter Content="{TemplateBinding Content}"
+                  <ContentPresenter x:Name="PART_ContentPresenter"
+                                    Content="{TemplateBinding Content}"
                                     ContentTemplate="{TemplateBinding ContentTemplate}" />
 
                   <Path Name="SortIcon"

src/Avalonia.Controls.DataGrid/Themes/Simple.xaml

@@ -66,7 +66,8 @@
                     HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                     VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                     ColumnDefinitions="*,Auto">
-                <ContentPresenter Content="{TemplateBinding Content}"
+                <ContentPresenter x:Name="PART_ContentPresenter"
+                                  Content="{TemplateBinding Content}"
                                   ContentTemplate="{TemplateBinding ContentTemplate}" />
 
                 <Path Name="SortIcon"

src/Avalonia.Controls/Chrome/CaptionButtons.cs

@@ -99,19 +99,28 @@ protected virtual void OnToggleFullScreen()
         protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
         {
             base.OnApplyTemplate(e);
+
+            if (e.NameScope.Find<Button>(PART_CloseButton) is { } closeButton)
+            {
+                closeButton.Click += (sender, e) => OnClose();
+            }
 
-            var closeButton = e.NameScope.Get<Button>(PART_CloseButton);
-            var restoreButton = e.NameScope.Get<Button>(PART_RestoreButton);
-            var minimizeButton = e.NameScope.Get<Button>(PART_MinimizeButton);
-            var fullScreenButton = e.NameScope.Get<Button>(PART_FullScreenButton);
-
-            closeButton.Click += (sender, e) => OnClose();
-            restoreButton.Click += (sender, e) => OnRestore();
-            minimizeButton.Click += (sender, e) => OnMinimize();
-            fullScreenButton.Click += (sender, e) => OnToggleFullScreen();
-
-            restoreButton.IsEnabled = HostWindow?.CanResize ?? true;
-            _restoreButton = restoreButton;
+            if (e.NameScope.Find<Button>(PART_RestoreButton) is { } restoreButton)
+            {
+                restoreButton.Click += (sender, e) => OnRestore();
+                restoreButton.IsEnabled = HostWindow?.CanResize ?? true;
+                _restoreButton = restoreButton;
+            }
+
+            if (e.NameScope.Find<Button>(PART_MinimizeButton) is { } minimizeButton)
+            {
+                minimizeButton.Click += (sender, e) => OnMinimize();
+            }
+
+            if (e.NameScope.Find<Button>(PART_FullScreenButton) is { } fullScreenButton)
+            {
+                fullScreenButton.Click += (sender, e) => OnToggleFullScreen();
+            }
         }
     }
 }

src/Avalonia.Controls/Chrome/TitleBar.cs

@@ -8,7 +8,7 @@ namespace Avalonia.Controls.Chrome
     /// <summary>
     /// Draws a titlebar when managed client decorations are enabled.
     /// </summary>
-    [TemplatePart("PART_CaptionButtons", typeof(CaptionButtons))]
+    [TemplatePart("PART_CaptionButtons", typeof(CaptionButtons), IsRequired = true)]
     [PseudoClasses(":minimized", ":normal", ":maximized", ":fullscreen")]
     public class TitleBar : TemplatedControl
     {

src/Avalonia.Controls/ComboBox.cs

@@ -17,7 +17,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// A drop-down list control.
     /// </summary>
-    [TemplatePart("PART_Popup", typeof(Popup))]
+    [TemplatePart("PART_Popup", typeof(Popup), IsRequired = true)]
     [PseudoClasses(pcDropdownOpen, pcPressed)]
     public class ComboBox : SelectingItemsControl
     {

src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs

@@ -13,22 +13,22 @@ namespace Avalonia.Controls
     /// Defines the presenter used for selecting a date for a 
     /// <see cref="DatePicker"/>
     /// </summary>
-    [TemplatePart("PART_AcceptButton",    typeof(Button))]
+    [TemplatePart("PART_AcceptButton",    typeof(Button), IsRequired = true)]
     [TemplatePart("PART_DayDownButton",   typeof(RepeatButton))]
-    [TemplatePart("PART_DayHost",         typeof(Panel))]
-    [TemplatePart("PART_DaySelector",     typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_DayHost",         typeof(Panel), IsRequired = true)]
+    [TemplatePart("PART_DaySelector",     typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_DayUpButton",     typeof(RepeatButton))]
     [TemplatePart("PART_DismissButton",   typeof(Button))]
     [TemplatePart("PART_FirstSpacer",     typeof(Rectangle))]
     [TemplatePart("PART_MonthDownButton", typeof(RepeatButton))]
-    [TemplatePart("PART_MonthHost",       typeof(Panel))]
-    [TemplatePart("PART_MonthSelector",   typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_MonthHost",       typeof(Panel), IsRequired = true)]
+    [TemplatePart("PART_MonthSelector",   typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_MonthUpButton",   typeof(RepeatButton))]
-    [TemplatePart("PART_PickerContainer", typeof(Grid))]
+    [TemplatePart("PART_PickerContainer", typeof(Grid), IsRequired = true)]
     [TemplatePart("PART_SecondSpacer",    typeof(Rectangle))]
     [TemplatePart("PART_YearDownButton",  typeof(RepeatButton))]
-    [TemplatePart("PART_YearHost",        typeof(Panel))]
-    [TemplatePart("PART_YearSelector",    typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_YearHost",        typeof(Panel), IsRequired = true)]
+    [TemplatePart("PART_YearSelector",    typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_YearUpButton",    typeof(RepeatButton))]
     public class DatePickerPresenter : PickerPresenterBase
     {

src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs

@@ -11,20 +11,20 @@ namespace Avalonia.Controls
     /// Defines the presenter used for selecting a time. Intended for use with
     /// <see cref="TimePicker"/> but can be used independently
     /// </summary>
-    [TemplatePart("PART_AcceptButton",     typeof(Button))]
+    [TemplatePart("PART_AcceptButton",     typeof(Button), IsRequired = true)]
     [TemplatePart("PART_DismissButton",    typeof(Button))]
     [TemplatePart("PART_HourDownButton",   typeof(RepeatButton))]
-    [TemplatePart("PART_HourSelector",     typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_HourSelector",     typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_HourUpButton",     typeof(RepeatButton))]
     [TemplatePart("PART_MinuteDownButton", typeof(RepeatButton))]
-    [TemplatePart("PART_MinuteSelector",   typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_MinuteSelector",   typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_MinuteUpButton",   typeof(RepeatButton))]
     [TemplatePart("PART_PeriodDownButton", typeof(RepeatButton))]
-    [TemplatePart("PART_PeriodHost",       typeof(Panel))]
-    [TemplatePart("PART_PeriodSelector",   typeof(DateTimePickerPanel))]
+    [TemplatePart("PART_PeriodHost",       typeof(Panel), IsRequired = true)]
+    [TemplatePart("PART_PeriodSelector",   typeof(DateTimePickerPanel), IsRequired = true)]
     [TemplatePart("PART_PeriodUpButton",   typeof(RepeatButton))]
-    [TemplatePart("PART_PickerContainer",  typeof(Grid))]
-    [TemplatePart("PART_SecondSpacer",     typeof(Rectangle))]
+    [TemplatePart("PART_PickerContainer",  typeof(Grid), IsRequired = true)]
+    [TemplatePart("PART_SecondSpacer",     typeof(Rectangle), IsRequired = true)]
     public class TimePickerPresenter : PickerPresenterBase
     {
         /// <summary>

src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs

@@ -19,7 +19,7 @@ namespace Avalonia.Controls
     /// Control that represents a TextBox with button spinners that allow incrementing and decrementing numeric values.
     /// </summary>
     [TemplatePart("PART_Spinner", typeof(Spinner))]
-    [TemplatePart("PART_TextBox", typeof(TextBox))]
+    [TemplatePart("PART_TextBox", typeof(TextBox), IsRequired = true)]
     public class NumericUpDown : TemplatedControl
     {
         /// <summary>

src/Avalonia.Controls/Primitives/HeaderedItemsControl.cs

@@ -1,5 +1,6 @@
 using System;
 using Avalonia.Collections;
+using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
@@ -10,6 +11,7 @@ namespace Avalonia.Controls.Primitives
     /// <summary>
     /// Represents an <see cref="ItemsControl"/> with a related header.
     /// </summary>
+    [TemplatePart("PART_HeaderPresenter", typeof(ContentPresenter))]
     public class HeaderedItemsControl : ItemsControl, IContentPresenterHost
     {
         private IDisposable? _itemsBinding;

src/Avalonia.Controls/ProgressBar.cs

@@ -13,7 +13,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// A control used to indicate the progress of an operation.
     /// </summary>
-    [TemplatePart("PART_Indicator", typeof(Border))]
+    [TemplatePart("PART_Indicator", typeof(Border), IsRequired = true)]
     [PseudoClasses(":vertical", ":horizontal", ":indeterminate")]
     public class ProgressBar : RangeBase
     {

src/Avalonia.Controls/Slider.cs

@@ -45,7 +45,7 @@ public enum TickPlacement
     /// </summary>
     [TemplatePart("PART_DecreaseButton", typeof(Button))]
     [TemplatePart("PART_IncreaseButton", typeof(Button))]
-    [TemplatePart("PART_Track",          typeof(Track))]
+    [TemplatePart("PART_Track",          typeof(Track), IsRequired = true)]
     [PseudoClasses(":vertical", ":horizontal", ":pressed")]
     public class Slider : RangeBase
     {
@@ -204,13 +204,10 @@ protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
             _pointerMovedDispose?.Dispose();
 
             _decreaseButton = e.NameScope.Find<Button>("PART_DecreaseButton");
-            _track = e.NameScope.Find<Track>("PART_Track");
+            _track = e.NameScope.Get<Track>("PART_Track");
             _increaseButton = e.NameScope.Find<Button>("PART_IncreaseButton");
 
-            if (_track != null)
-            {
-                _track.IgnoreThumbDrag = true;
-            }
+            _track.IgnoreThumbDrag = true;
 
             if (_decreaseButton != null)
             {

src/Avalonia.Controls/TabControl.cs

@@ -18,6 +18,7 @@ namespace Avalonia.Controls
     /// A tab control that displays a tab strip along with the content of the selected tab.
     /// </summary>
     [TemplatePart("PART_ItemsPresenter", typeof(ItemsPresenter))]
+    [TemplatePart("PART_SelectedContentHost", typeof(ContentPresenter))]
     public class TabControl : SelectingItemsControl, IContentPresenterHost
     {
         private object? _selectedContent;

src/Avalonia.Controls/TextBox.cs

@@ -24,7 +24,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// Represents a control that can be used to display or edit unformatted text.
     /// </summary>
-    [TemplatePart("PART_TextPresenter", typeof(TextPresenter))]
+    [TemplatePart("PART_TextPresenter", typeof(TextPresenter), IsRequired = true)]
     [TemplatePart("PART_ScrollViewer", typeof(ScrollViewer))]
     [PseudoClasses(":empty")]
     public class TextBox : TemplatedControl, UndoRedoHelper<TextBox.UndoRedoState>.IUndoRedoHost

src/Avalonia.Controls/ToggleSwitch.cs

@@ -11,7 +11,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// A Toggle Switch control.
     /// </summary>
-    [TemplatePart("PART_MovingKnobs",         typeof(Panel))]
+    [TemplatePart("PART_MovingKnobs",         typeof(Panel), IsRequired = true)]
     [TemplatePart("PART_OffContentPresenter", typeof(ContentPresenter))]
     [TemplatePart("PART_OnContentPresenter",  typeof(ContentPresenter))]
     [TemplatePart("PART_SwitchKnob",          typeof(Panel))]

src/Avalonia.Dialogs/ManagedFileChooser.cs

@@ -11,8 +11,8 @@
 
 namespace Avalonia.Dialogs
 {
-    [TemplatePart("PART_QuickLinks", typeof(Control))]
-    [TemplatePart("PART_Files",      typeof(ListBox))]
+    [TemplatePart("PART_QuickLinks", typeof(Control), IsRequired = true)]
+    [TemplatePart("PART_Files",      typeof(ListBox), IsRequired = true)]
     public class ManagedFileChooser : TemplatedControl
     {
         private Control? _quickLinksRoot;

src/Avalonia.Themes.Fluent/Controls/CalendarButton.xaml

@@ -35,7 +35,7 @@
           <!-- To mimic WinUI SystemFocusVisual, Focus visual is drawn outside the bounds of the item -->
           <Border Name="Root" Background="{TemplateBinding Background}"
                   BorderThickness="0" ClipToBounds="True">
-            <ContentPresenter Name="Content"
+            <ContentPresenter Name="PART_ContentPresenter"
                               ContentTemplate="{TemplateBinding ContentTemplate}"
                               Content="{TemplateBinding Content}"
                               HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"

src/Avalonia.Themes.Fluent/Controls/CalendarDayButton.xaml

@@ -36,12 +36,12 @@
           <Border Name="Root" Background="{TemplateBinding Background}"
                   BorderThickness="0" ClipToBounds="True">
 
-            <ContentControl Name="Content"
-                            ContentTemplate="{TemplateBinding ContentTemplate}"
-                            Content="{TemplateBinding Content}"
-                            HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
-                            VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
-                            Margin="{TemplateBinding Padding}" />
+            <ContentPresenter Name="PART_ContentPresenter"
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
+                              Content="{TemplateBinding Content}"
+                              HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
+                              VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
+                              Margin="{TemplateBinding Padding}" />
 
           </Border>
 

src/Avalonia.Themes.Fluent/Controls/CalendarItem.xaml

@@ -31,7 +31,7 @@
     <Setter Property="Template">
       <ControlTemplate>
         <!-- HCA was changed here to ensure nav arrows display correctly -->
-        <ContentPresenter Name="Text" Background="{TemplateBinding Background}"
+        <ContentPresenter Name="PART_ContentPresenter" Background="{TemplateBinding Background}"
                           BorderBrush="{DynamicResource CalendarViewNavigationButtonBorderBrush}"
                           BorderThickness="{TemplateBinding BorderThickness}"
                           Content="{TemplateBinding Content}"

src/Avalonia.Themes.Fluent/Controls/CheckBox.xaml

@@ -55,7 +55,7 @@
               </Panel>
             </Viewbox>
           </Grid>
-          <ContentPresenter x:Name="ContentPresenter"
+          <ContentPresenter x:Name="PART_ContentPresenter"
                           ContentTemplate="{TemplateBinding ContentTemplate}"
                           Content="{TemplateBinding Content}"
                           Margin="{TemplateBinding Padding}"

src/Avalonia.Themes.Fluent/Controls/DateTimePickerShared.xaml

@@ -55,7 +55,7 @@
                 that appear opaque. Not sure how MS does it though I suspect this is it
                 but source isn't MIT yet, so this is my solution -->
         <Border Background="{TemplateBinding Background}">
-          <ContentPresenter x:Name="ContentPresenter"
+          <ContentPresenter x:Name="PART_ContentPresenter"
                   Background="{TemplateBinding Background}"
                   BorderBrush="{DynamicResource DateTimePickerFlyoutButtonBorderBrush}"
                   BorderThickness="{DynamicResource DateTimeFlyoutButtonBorderThickness}"

src/Avalonia.Themes.Fluent/Controls/FlyoutPresenter.xaml

@@ -26,7 +26,8 @@
                 CornerRadius="{TemplateBinding CornerRadius}">
           <ScrollViewer HorizontalScrollBarVisibility="{TemplateBinding ScrollViewer.HorizontalScrollBarVisibility}"
                         VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}">
-            <ContentPresenter Content="{TemplateBinding Content}"
+            <ContentPresenter x:Name="PART_ContentPresenter"
+                              Content="{TemplateBinding Content}"
                               ContentTemplate="{TemplateBinding ContentTemplate}"
                               Margin="{TemplateBinding Padding}"
                               HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"

src/Avalonia.Themes.Fluent/Controls/NotificationCard.xaml

@@ -25,7 +25,7 @@
                     ClipToBounds="True">
               <DockPanel>
                 <Panel x:Name="PART_HeaderBar" Height="4" Background="{DynamicResource NotificationCardProgressBackgroundBrush}" DockPanel.Dock="Top" />
-                <ContentControl Name="PART_Content" MinHeight="64" Content="{TemplateBinding Content}" />
+                <ContentPresenter Name="PART_ContentPresenter" MinHeight="64" Content="{TemplateBinding Content}" />
               </DockPanel>
             </Border>
           </Border>

src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml

@@ -63,7 +63,8 @@
     <Setter Property="TextElement.Foreground" Value="{DynamicResource ScrollBarButtonArrowForeground}"/>
     <Setter Property="Template">
       <ControlTemplate>
-        <ContentPresenter Background="{DynamicResource ScrollBarButtonBackground}"
+        <ContentPresenter x:Name="PART_ContentPresenter"
+                          Background="{DynamicResource ScrollBarButtonBackground}"
                           BorderBrush="{DynamicResource ScrollBarButtonBorderBrush}"
                           Content="{TemplateBinding Content}"/>
       </ControlTemplate>

src/Avalonia.Themes.Simple/Controls/CalendarButton.xaml

@@ -33,7 +33,7 @@
                      Opacity="0.5" />
 
           <!--  Focusable="False"  -->
-          <ContentPresenter Name="Content"
+          <ContentPresenter x:Name="PART_ContentPresenter"
                             Margin="1,0,1,1"
                             HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                             VerticalAlignment="{TemplateBinding VerticalContentAlignment}"