Fix endpoints not retaining state

Needlework.Net/ViewLocator.cs

@@ -1,28 +1,40 @@
 using Avalonia.Controls;
 using Avalonia.Controls.Templates;
 using System;
+using System.Collections.Generic;
 using System.ComponentModel;
 
 namespace Needlework.Net
 {
     public class ViewLocator : IDataTemplate
     {
-        public Control? Build(object? param)
-        {
-            if (param is null) return new TextBlock { Text = "data was null" };
+        private readonly Dictionary<object, Control> _controlCache = [];
 
-            var name = param.GetType().FullName!
-                .Replace("ViewModels", "Views")
-                .Replace("ViewModel", "View");
+        public Control Build(object? data)
+        {
+            var fullName = data?.GetType().FullName;
+            if (fullName is null)
+            {
+                return new TextBlock { Text = "Data is null or has no name." };
+            }
+
+            var name = fullName.Replace("ViewModel", "View");
             var type = Type.GetType(name);
+            if (type is null)
+            {
+                return new TextBlock { Text = $"No View For {name}." };
+            }
 
-            if (type != null) return (Control)Activator.CreateInstance(type)!;
-            else return new TextBlock { Text = "Not Found: " + name };
+            if (!_controlCache.TryGetValue(data!, out var res))
+            {
+                res ??= (Control)Activator.CreateInstance(type)!;
+                _controlCache[data!] = res;
+            }
+
+            res.DataContext = data;
+            return res;
         }
 
-        public bool Match(object? data)
-        {
-            return data is INotifyPropertyChanged;
-        }
+        public bool Match(object? data) => data is INotifyPropertyChanged;
     }
 }