Reduce overhead of compiling regex

Use INotifyDataErrorInfo to signal error

src/Avalonia.Diagnostics/Diagnostics/ViewModels/ControlDetailsViewModel.cs

@@ -132,8 +132,7 @@ namespace Avalonia.Diagnostics.ViewModels
             {
                 if (TreePage.UseRegexFilter)
                 {
-                    var regex = new Regex(TreePage.PropertyFilter);
-                    return regex.IsMatch(property.Name);
+                    return TreePage.FilterRegex?.IsMatch(property.Name) ?? true;
                 }
 
                 return property.Name.IndexOf(TreePage.PropertyFilter, StringComparison.OrdinalIgnoreCase) != -1;

src/Avalonia.Diagnostics/Diagnostics/ViewModels/TreePageViewModel.cs

@@ -1,11 +1,16 @@
 using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Text.RegularExpressions;
 using Avalonia.Controls;
 using Avalonia.VisualTree;
 
 namespace Avalonia.Diagnostics.ViewModels
 {
-    internal class TreePageViewModel : ViewModelBase, IDisposable
+    internal class TreePageViewModel : ViewModelBase, IDisposable, INotifyDataErrorInfo
     {
+        private readonly Dictionary<string, string> _errors = new Dictionary<string, string>();
         private TreeNode _selectedNode;
         private ControlDetailsViewModel _details;
         private string _propertyFilter = string.Empty;
@@ -14,17 +19,13 @@ namespace Avalonia.Diagnostics.ViewModels
         public TreePageViewModel(TreeNode[] nodes)
         {
             Nodes = nodes;
-            Selection = new SelectionModel
-            { 
-                SingleSelect = true,
-                Source = Nodes 
-            };
+            Selection = new SelectionModel { SingleSelect = true, Source = Nodes };
 
             Selection.SelectionChanged += (s, e) =>
             {
                 SelectedNode = (TreeNode)Selection.SelectedItem;
             };
-       }
+        }
 
         public TreeNode[] Nodes { get; protected set; }
 
@@ -58,6 +59,37 @@ namespace Avalonia.Diagnostics.ViewModels
             }
         }
 
+        public Regex FilterRegex { get; set; }
+
+        private void UpdateFilterRegex()
+        {
+            void ClearError()
+            {
+                if (_errors.Remove(nameof(PropertyFilter)))
+                {
+                    ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(nameof(PropertyFilter)));
+                }
+            }
+
+            if (UseRegexFilter)
+            {
+                try
+                {
+                    FilterRegex = new Regex(PropertyFilter);
+                    ClearError();
+                }
+                catch (Exception exception)
+                {
+                    _errors[nameof(PropertyFilter)] = exception.Message;
+                    ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(nameof(PropertyFilter)));
+                }
+            }
+            else
+            {
+                ClearError();
+            }
+        }
+
         public string PropertyFilter
         {
             get => _propertyFilter;
@@ -65,6 +97,7 @@ namespace Avalonia.Diagnostics.ViewModels
             {
                 if (RaiseAndSetIfChanged(ref _propertyFilter, value))
                 {
+                    UpdateFilterRegex();
                     Details.PropertiesView.Refresh();
                 }
             }
@@ -77,6 +110,7 @@ namespace Avalonia.Diagnostics.ViewModels
             {
                 if (RaiseAndSetIfChanged(ref _useRegexFilter, value))
                 {
+                    UpdateFilterRegex();
                     Details.PropertiesView.Refresh();
                 }
             }
@@ -158,5 +192,17 @@ namespace Avalonia.Diagnostics.ViewModels
 
             return null;
         }
+
+        public IEnumerable GetErrors(string propertyName)
+        {
+            if (_errors.TryGetValue(propertyName, out var error))
+            {
+                yield return error;
+            }
+        }
+
+        public bool HasErrors => _errors.Count > 0;
+
+        public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;
     }
 }