Improve debug display of controls and related error messages (#15219)

* Improve debug display of controls and related error messages

* Move DebugDisplayHelper

---------

Co-authored-by: Max Katz <maxkatz6@outlook.com>

src/Avalonia.Base/Animation/AnimatorKeyFrame.cs

@@ -1,6 +1,7 @@
 using System;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
+using System.Text;
 using Avalonia.Animation.Animators;
 using Avalonia.Data;
 using Avalonia.Reactive;
@@ -75,5 +76,13 @@ namespace Avalonia.Animation
 
             return (T)typeConv.ConvertTo(Value, typeof(T))!;
         }
+
+        internal override void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            base.BuildDebugDisplay(builder, includeContent);
+            DebugDisplayHelper.AppendOptionalValue(builder, nameof(Property), Property, includeContent);
+            DebugDisplayHelper.AppendOptionalValue(builder, nameof(Cue), Cue, includeContent);
+            DebugDisplayHelper.AppendOptionalValue(builder, nameof(Value), Value, includeContent);
+        }
     }
 }

src/Avalonia.Base/Animation/Animators/TransformOperationsAnimator.cs

@@ -1,14 +1,15 @@
 using System;
+using Avalonia.Collections;
 using Avalonia.Media;
 using Avalonia.Media.Transformation;
 
 namespace Avalonia.Animation.Animators
 {
-    internal class TransformOperationsAnimator : Animator<TransformOperations>
+    internal class TransformOperationsAnimator : Animator<TransformOperations>, IAvaloniaListItemValidator<AnimatorKeyFrame>
     {
         public TransformOperationsAnimator()
         {
-            Validate = ValidateTransform;
+            Validator = this;
         }
 
         public override TransformOperations Interpolate(double progress, TransformOperations oldValue, TransformOperations newValue)
@@ -24,11 +25,11 @@ namespace Avalonia.Animation.Animators
             return value as TransformOperations ?? TransformOperations.Identity;
         }
 
-        private void ValidateTransform(AnimatorKeyFrame kf)
+        void IAvaloniaListItemValidator<AnimatorKeyFrame>.Validate(AnimatorKeyFrame item)
         {
-            if (!(kf.Value is TransformOperations))
+            if (item.Value is not TransformOperations)
             {
-                throw new InvalidOperationException($"All keyframes must be of type {typeof(TransformOperations)}.");
+                throw new InvalidOperationException($"{item.DebugDisplay} must have a value of type {typeof(TransformOperations)}.");
             }
         }
     }

src/Avalonia.Base/Animation/KeyFrame.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Text;
 using Avalonia.Collections;
 using Avalonia.Metadata;
 
@@ -95,6 +96,20 @@ namespace Avalonia.Animation
             }
         }
 
+        internal override void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            base.BuildDebugDisplay(builder, includeContent);
+
+            switch (TimingMode)
+            {
+                case KeyFrameTimingMode.TimeSpan:
+                    DebugDisplayHelper.AppendOptionalValue(builder, nameof(KeyTime), KeyTime, includeContent);
+                    break;
+                case KeyFrameTimingMode.Cue:
+                    DebugDisplayHelper.AppendOptionalValue(builder, nameof(Cue), Cue, includeContent);
+                    break;
+            }
+        }
     }
 
 }

src/Avalonia.Base/Animation/TransitionBase.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
+using System.Text;
 using Avalonia.Animation.Easings;
 
 namespace Avalonia.Animation
@@ -96,5 +97,12 @@ namespace Avalonia.Animation
             => Apply(control, clock, oldValue, newValue);
         
         internal abstract IDisposable Apply(Animatable control, IClock clock, object? oldValue, object? newValue);
+
+        internal override void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            base.BuildDebugDisplay(builder, includeContent);
+            DebugDisplayHelper.AppendOptionalValue(builder, nameof(Property), Property, includeContent);
+            DebugDisplayHelper.AppendOptionalValue(builder, nameof(Duration), Duration, includeContent);
+        }
     }
 }

src/Avalonia.Base/Animation/Transitions.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation
     /// <summary>
     /// A collection of <see cref="ITransition"/> definitions.
     /// </summary>
-    public sealed class Transitions : AvaloniaList<ITransition>
+    public sealed class Transitions : AvaloniaList<ITransition>, IAvaloniaListItemValidator<ITransition>
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="Transitions"/> class.
@@ -15,16 +15,18 @@ namespace Avalonia.Animation
         public Transitions()
         {
             ResetBehavior = ResetBehavior.Remove;
-            Validate = ValidateTransition;
+            Validator = this;
         }
 
-        private void ValidateTransition(ITransition obj)
+        void IAvaloniaListItemValidator<ITransition>.Validate(ITransition item)
         {
             Dispatcher.UIThread.VerifyAccess();
 
-            if (obj.Property.IsDirect)
+            var property = item.Property;
+            if (property.IsDirect)
             {
-                throw new InvalidOperationException("Cannot animate a direct property.");
+                var display = item is TransitionBase transition ? transition.DebugDisplay : item.ToString();
+                throw new InvalidOperationException($"Cannot animate direct property {property} on {display}.");
             }
         }
     }

src/Avalonia.Base/AvaloniaObject.cs

@@ -1,7 +1,9 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Diagnostics;
 using System.Runtime.CompilerServices;
+using System.Text;
 using Avalonia.Data;
 using Avalonia.Data.Core;
 using Avalonia.Diagnostics;
@@ -18,6 +20,7 @@ namespace Avalonia
     /// <remarks>
     /// This class is analogous to DependencyObject in WPF.
     /// </remarks>
+    [DebuggerDisplay("{DebugDisplay}")]
     public class AvaloniaObject : IAvaloniaObjectDebug, INotifyPropertyChanged
     {
         private readonly ValueStore _values;
@@ -101,6 +104,11 @@ namespace Avalonia
             set { this.Bind(binding.Property!, value); }
         }
 
+        /// <summary>
+        /// Gets a string to display inside the debugger for this object.
+        /// </summary>
+        internal string DebugDisplay => GetDebugDisplay(true);
+
         /// <summary>
         /// Returns a value indicating whether the current thread is the UI thread.
         /// </summary>
@@ -860,6 +868,28 @@ namespace Avalonia
                 priority);
         }
 
+        internal string GetDebugDisplay(bool includeContent)
+        {
+            var builder = new StringBuilder();
+            BuildDebugDisplay(builder, includeContent);
+            return builder.ToString();
+        }
+
+        internal virtual void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            var type = GetType();
+
+            if (type.Namespace is { } ns &&
+                (ns == "Avalonia" || ns.StartsWith("Avalonia.", StringComparison.Ordinal)))
+            {
+                builder.Append(type.Name);
+            }
+            else
+            {
+                builder.Append(ToString());
+            }
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static void ValidatePriority(BindingPriority priority)
         {

src/Avalonia.Base/Collections/AvaloniaList.cs

@@ -115,7 +115,34 @@ namespace Avalonia.Collections
         /// Gets or sets a validation routine that can be used to validate items before they are
         /// added.
         /// </summary>
-        public Action<T>? Validate { get; set; }
+        public Action<T>? Validate
+        {
+            get => Validator switch
+            {
+                null => null,
+                ItemValidator itemValidator => itemValidator.Validate,
+                { } other => other.Validate
+            };
+            set
+            {
+                if (value is null)
+                {
+                    Validator = null;
+                    return;
+                }
+
+                if (Validator is ItemValidator itemValidator)
+                {
+                    itemValidator.Validate = value;
+                }
+                else
+                {
+                    Validator = new ItemValidator(value);
+                }
+            }
+        }
+
+        internal IAvaloniaListItemValidator<T>? Validator { get; set; }
 
         /// <inheritdoc/>
         bool IList.IsFixedSize => false;
@@ -149,7 +176,7 @@ namespace Avalonia.Collections
 
             set
             {
-                Validate?.Invoke(value);
+                Validator?.Validate(value);
 
                 T old = _inner[index];
 
@@ -196,7 +223,7 @@ namespace Avalonia.Collections
         /// <param name="item">The item.</param>
         public virtual void Add(T item)
         {
-            Validate?.Invoke(item);
+            Validator?.Validate(item);
             int index = _inner.Count;
             _inner.Add(item);
             NotifyAdd(item, index);
@@ -303,7 +330,7 @@ namespace Avalonia.Collections
         /// <param name="item">The item.</param>
         public virtual void Insert(int index, T item)
         {
-            Validate?.Invoke(item);
+            Validator?.Validate(item);
             _inner.Insert(index, item);
             NotifyAdd(item, index);
         }
@@ -318,7 +345,7 @@ namespace Avalonia.Collections
             _ = items ?? throw new ArgumentNullException(nameof(items));
 
             bool willRaiseCollectionChanged = _collectionChanged != null;
-            bool hasValidation = Validate != null;
+            bool hasValidation = Validator is not null;
 
             if (items is IList list)
             {
@@ -330,7 +357,7 @@ namespace Avalonia.Collections
                         {
                             foreach (T item in collection)
                             {
-                                Validate!(item);
+                                Validator!.Validate(item);
                             }
                         }
 
@@ -351,7 +378,7 @@ namespace Avalonia.Collections
 
                                 if (hasValidation)
                                 {
-                                    Validate!(item);
+                                    Validator!.Validate(item);
                                 }
 
                                 _inner.Insert(insertIndex++, item);
@@ -381,7 +408,7 @@ namespace Avalonia.Collections
 
                             if (hasValidation)
                             {
-                                Validate!(item);
+                                Validator!.Validate(item);
                             }
 
                             _inner.Insert(insertIndex++, item);
@@ -772,6 +799,17 @@ namespace Avalonia.Collections
                 _innerEnumerator.Dispose();
             }
         }
+
+        private sealed class ItemValidator : IAvaloniaListItemValidator<T>
+        {
+            public ItemValidator(Action<T> validate)
+                => Validate = validate;
+
+            public Action<T> Validate { get; set; }
+
+            void IAvaloniaListItemValidator<T>.Validate(T item)
+                => Validate(item);
+        }
     }
 
     internal static class EventArgsCache

src/Avalonia.Base/Collections/IAvaloniaListItemValidator.cs

@@ -0,0 +1,6 @@
+namespace Avalonia.Collections;
+
+internal interface IAvaloniaListItemValidator<T>
+{
+    void Validate(T item);
+}

src/Avalonia.Base/Diagnostics/DebugDisplayHelper.cs

@@ -0,0 +1,49 @@
+using System.Text;
+
+namespace Avalonia;
+
+internal static class DebugDisplayHelper
+{
+    public static void AppendOptionalValue(StringBuilder builder, string name, object? value, bool includeContent)
+    {
+        const int maxValueLength = 50;
+
+        if (value is null or string { Length: 0 })
+        {
+            return;
+        }
+
+        if (builder.Length > 0 && builder[builder.Length - 1] == ')')
+        {
+            --builder.Length;
+            builder.Append(", ");
+        }
+        else
+        {
+            builder.Append(" (");
+        }
+
+        builder.Append(name);
+        builder.Append(" = ");
+
+        if (value is AvaloniaObject avaloniaObject)
+        {
+            avaloniaObject.BuildDebugDisplay(builder, includeContent);
+        }
+        else
+        {
+            var stringValue = value.ToString();
+            if (stringValue?.Length > maxValueLength)
+            {
+                builder.Append(stringValue, 0, maxValueLength - 1);
+                builder.Append('…');
+            }
+            else
+            {
+                builder.Append(stringValue);
+            }
+        }
+
+        builder.Append(')');
+    }
+}

src/Avalonia.Base/StyledElement.cs

@@ -4,7 +4,7 @@ using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Diagnostics;
-using System.Linq;
+using System.Text;
 using Avalonia.Animation;
 using Avalonia.Collections;
 using Avalonia.Controls;
@@ -34,6 +34,7 @@ namespace Avalonia
         ISetInheritanceParent,
         ISupportInitialize,
         INamed,
+        IAvaloniaListItemValidator<ILogical>,
 #pragma warning disable CS0618 // Type or member is obsolete
         IStyleable
 #pragma warning restore CS0618 // Type or member is obsolete
@@ -277,7 +278,7 @@ namespace Avalonia
                     var list = new AvaloniaList<ILogical>
                     {
                         ResetBehavior = ResetBehavior.Remove,
-                        Validate = logical => ValidateLogicalChild(logical)
+                        Validator = this
                     };
                     list.CollectionChanged += LogicalChildrenCollectionChanged;
                     _logicalChildren = list;
@@ -787,11 +788,11 @@ namespace Avalonia
             return null;
         }
 
-        private static void ValidateLogicalChild(ILogical c)
+        void IAvaloniaListItemValidator<ILogical>.Validate(ILogical item)
         {
-            if (c == null)
+            if (item is null)
             {
-                throw new ArgumentException("Cannot add null to LogicalChildren.");
+                throw new ArgumentException($"Cannot add null to {nameof(LogicalChildren)}.");
             }
         }
 
@@ -1018,6 +1019,12 @@ namespace Avalonia
             }
         }
 
+        internal override void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            base.BuildDebugDisplay(builder, includeContent);
+            DebugDisplayHelper.AppendOptionalValue(builder, nameof(Name), Name, includeContent);
+        }
+
         private static IReadOnlyList<Style>? FlattenStyles(IReadOnlyList<IStyle> styles)
         {
             List<Style>? result = null;

src/Avalonia.Base/Styling/Styles.cs

@@ -14,7 +14,8 @@ namespace Avalonia.Styling
     public class Styles : AvaloniaObject,
         IAvaloniaList<IStyle>,
         IStyle,
-        IResourceProvider
+        IResourceProvider,
+        IAvaloniaListItemValidator<IStyle>
     {
         private readonly AvaloniaList<IStyle> _styles = new();
         private IResourceHost? _owner;
@@ -24,11 +25,7 @@ namespace Avalonia.Styling
         {
             _styles.ResetBehavior = ResetBehavior.Remove;
             _styles.CollectionChanged += OnCollectionChanged;
-            _styles.Validate = i =>
-            {
-                if (i is ControlTheme)
-                    throw new InvalidOperationException("ControlThemes cannot be added to a Styles collection.");
-            };
+            _styles.Validator = this;
         }
 
         public Styles(IResourceHost owner)
@@ -311,5 +308,14 @@ namespace Avalonia.Styling
 
             CollectionChanged?.Invoke(this, e);
         }
+
+        void IAvaloniaListItemValidator<IStyle>.Validate(IStyle item)
+        {
+            if (item is ControlTheme theme)
+            {
+                throw new InvalidOperationException(
+                    $"{nameof(ControlTheme)} (for {theme.TargetType}) cannot be added to a {nameof(Styles)} collection.");
+            }
+        }
     }
 }

src/Avalonia.Base/Threading/DispatcherOperation.cs

@@ -1,6 +1,7 @@
 using System;
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
+using System.Runtime.ExceptionServices;
 using System.Threading;
 using System.Threading.Tasks;
 

src/Avalonia.Base/Visual.cs

@@ -29,7 +29,7 @@ namespace Avalonia
     /// extension methods defined in <see cref="VisualExtensions"/>.
     /// </remarks>
     [UsableDuringInitialization]
-    public partial class Visual : StyledElement
+    public partial class Visual : StyledElement, IAvaloniaListItemValidator<Visual>
     {
         /// <summary>
         /// Defines the <see cref="Bounds"/> property.
@@ -150,7 +150,7 @@ namespace Avalonia
 
             var visualChildren = new AvaloniaList<Visual>();
             visualChildren.ResetBehavior = ResetBehavior.Remove;
-            visualChildren.Validate = visual => ValidateVisualChild(visual);
+            visualChildren.Validator = this;
             visualChildren.CollectionChanged += VisualChildrenChanged;
             VisualChildren = visualChildren;
         }
@@ -618,17 +618,19 @@ namespace Avalonia
         /// <summary>
         /// Ensures a visual child is not null and not already parented.
         /// </summary>
-        /// <param name="c">The visual child.</param>
-        private static void ValidateVisualChild(Visual c)
+        /// <param name="item">The visual child.</param>
+        void IAvaloniaListItemValidator<Visual>.Validate(Visual item)
         {
-            if (c == null)
+            if (item is null)
             {
-                throw new ArgumentNullException(nameof(c), "Cannot add null to VisualChildren.");
+                throw new ArgumentNullException(nameof(item), $"Cannot add null to {nameof(VisualChildren)}.");
             }
 
-            if (c.VisualParent != null)
+            if (item.VisualParent is { } parent)
             {
-                throw new InvalidOperationException("The control already has a visual parent.");
+                throw new InvalidOperationException(
+                    $"The control {item.DebugDisplay} already has a visual parent {parent.GetDebugDisplay(false)} " +
+                    $"while trying to add it as a child of {GetDebugDisplay(false)}.");
             }
         }
 

src/Avalonia.Controls/ContentControl.cs

@@ -1,6 +1,6 @@
+using System.Text;
 using Avalonia.Collections;
 using Avalonia.Controls.Metadata;
-using Avalonia.Controls.Mixins;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
@@ -152,5 +152,15 @@ namespace Avalonia.Controls
                 LogicalChildren.Add(newChild);
             }
         }
+
+        internal override void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            base.BuildDebugDisplay(builder, includeContent);
+
+            if (includeContent)
+            {
+                DebugDisplayHelper.AppendOptionalValue(builder, nameof(Content), Content, includeContent);
+            }
+        }
     }
 }

src/Avalonia.Controls/Controls.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// A collection of <see cref="Control"/>s.
     /// </summary>
-    public class Controls : AvaloniaList<Control>
+    public class Controls : AvaloniaList<Control>, IAvaloniaListItemValidator<Control>
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="Controls"/> class.
@@ -30,14 +30,17 @@ namespace Avalonia.Controls
         private void Configure()
         {
             ResetBehavior = ResetBehavior.Remove;
-            Validate = item =>
+            Validator = this;
+        }
+
+        void IAvaloniaListItemValidator<Control>.Validate(Control item)
+        {
+            if (item is null)
             {
-                if (item is null)
-                {
-                    throw new ArgumentNullException(nameof(item),
-                        $"A null control cannot be added to a {nameof(Controls)} collection.");
-                }
-            };
+                throw new ArgumentNullException(
+                    nameof(item),
+                    $"A null control cannot be added to a {nameof(Controls)} collection.");
+            }
         }
     }
 }

src/Avalonia.Controls/NativeMenu.cs

@@ -7,7 +7,10 @@ using Avalonia.Metadata;
 
 namespace Avalonia.Controls
 {
-    public partial class NativeMenu : AvaloniaObject, IEnumerable<NativeMenuItemBase>, INativeMenuExporterEventsImplBridge
+    public partial class NativeMenu : AvaloniaObject,
+        IEnumerable<NativeMenuItemBase>,
+        INativeMenuExporterEventsImplBridge,
+        IAvaloniaListItemValidator<NativeMenuItemBase>
     {
         private readonly AvaloniaList<NativeMenuItemBase> _items =
             new AvaloniaList<NativeMenuItemBase> { ResetBehavior = ResetBehavior.Remove };
@@ -43,7 +46,7 @@ namespace Avalonia.Controls
 
         public NativeMenu()
         {
-            _items.Validate = Validator;
+            _items.Validator = this;
             _items.CollectionChanged += ItemsChanged;
         }
 
@@ -62,10 +65,14 @@ namespace Avalonia.Controls
             Closed?.Invoke(this, EventArgs.Empty);
         }
 
-        private void Validator(NativeMenuItemBase obj)
+        void IAvaloniaListItemValidator<NativeMenuItemBase>.Validate(NativeMenuItemBase item)
         {
-            if (obj.Parent != null)
-                throw new InvalidOperationException("NativeMenuItem already has a parent");
+            if (item.Parent is { } parent)
+            {
+                throw new InvalidOperationException(
+                    $"The menu item {item.DebugDisplay} already has a parent {parent.DebugDisplay} " +
+                    $"while trying to add it as a child of {DebugDisplay}.");
+            }
         }
 
         private void ItemsChanged(object? sender, NotifyCollectionChangedEventArgs e)

src/Avalonia.Controls/NativeMenuItem.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Text;
 using System.Windows.Input;
 using Avalonia.Controls.Primitives;
 using Avalonia.Input;
@@ -216,6 +217,16 @@ namespace Avalonia.Controls
                 CanExecuteChanged();
             }
         }
+
+        internal override void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            base.BuildDebugDisplay(builder, includeContent);
+
+            if (includeContent)
+            {
+                DebugDisplayHelper.AppendOptionalValue(builder, nameof(Header), Header, true);
+            }
+        }
     }
 
     // TODO12: remove this enum and use MenuItemToggleType only 

src/Avalonia.Controls/Presenters/ContentPresenter.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Text;
 using Avalonia.Collections;
 using Avalonia.Controls.Documents;
 using Avalonia.Controls.Metadata;
@@ -721,5 +722,17 @@ namespace Avalonia.Controls.Presenters
             var host = e.NewValue as IContentPresenterHost;
             Host = host?.RegisterContentPresenter(this) == true ? host : null;
         }
+
+        internal override void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            base.BuildDebugDisplay(builder, includeContent);
+
+            DebugDisplayHelper.AppendOptionalValue(builder, nameof(Host), Host, false);
+
+            if (includeContent)
+            {
+                DebugDisplayHelper.AppendOptionalValue(builder, nameof(Content), Content, true);
+            }
+        }
     }
 }

src/Avalonia.Controls/Primitives/HeaderedContentControl.cs

@@ -1,3 +1,4 @@
+using System.Text;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
@@ -84,5 +85,15 @@ namespace Avalonia.Controls.Primitives
                 LogicalChildren.Add(newChild);
             }
         }
+
+        internal override void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            base.BuildDebugDisplay(builder, includeContent);
+
+            if (includeContent)
+            {
+                DebugDisplayHelper.AppendOptionalValue(builder, nameof(Header), Header, true);
+            }
+        }
     }
 }

src/Avalonia.Controls/Templates/DataTemplates.cs

@@ -6,7 +6,7 @@ namespace Avalonia.Controls.Templates
     /// <summary>
     /// A collection of <see cref="IDataTemplate"/>s.
     /// </summary>
-    public class DataTemplates : AvaloniaList<IDataTemplate>
+    public class DataTemplates : AvaloniaList<IDataTemplate>, IAvaloniaListItemValidator<IDataTemplate>
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="DataTemplates"/> class.
@@ -14,13 +14,12 @@ namespace Avalonia.Controls.Templates
         public DataTemplates()
         {
             ResetBehavior = ResetBehavior.Remove;
-            
-            Validate += ValidateDataTemplate;
+            Validator = this;
         }
 
-        private static void ValidateDataTemplate(IDataTemplate template)
+        void IAvaloniaListItemValidator<IDataTemplate>.Validate(IDataTemplate item)
         {
-            var valid = template switch
+            var valid = item switch
             {
                 ITypedDataTemplate typed => typed.DataType is not null,
                 _ => true
@@ -32,4 +31,4 @@ namespace Avalonia.Controls.Templates
             }
         }
     }
-}
+}

src/Avalonia.Controls/TextBlock.cs

@@ -1,6 +1,6 @@
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
+using System.Text;
 using Avalonia.Automation.Peers;
 using Avalonia.Collections;
 using Avalonia.Controls.Documents;
@@ -15,7 +15,6 @@ namespace Avalonia.Controls
     /// <summary>
     /// A control that displays a block of text.
     /// </summary>
-    [DebuggerDisplay("Text = {" + nameof(DebugText) + "}")]
     public class TextBlock : Control, IInlineHost
     {
         /// <summary>
@@ -218,8 +217,6 @@ namespace Avalonia.Controls
             set => SetValue(TextProperty, value);
         }
 
-        private string? DebugText => Text ?? Inlines?.Text;
-
         /// <summary>
         /// Gets or sets the font family used to draw the control's text.
         /// </summary>
@@ -862,6 +859,16 @@ namespace Avalonia.Controls
 
         IAvaloniaList<Visual> IInlineHost.VisualChildren => VisualChildren;
 
+        internal override void BuildDebugDisplay(StringBuilder builder, bool includeContent)
+        {
+            base.BuildDebugDisplay(builder, includeContent);
+
+            if (includeContent)
+            {
+                DebugDisplayHelper.AppendOptionalValue(builder, nameof(Text), Text ?? Inlines?.Text, true);
+            }
+        }
+
         protected readonly record struct SimpleTextSource : ITextSource
         {
             private readonly string _text;