improve async task command handling

Author: DerekGooding

SimpleViewModel/BaseClasses/BaseViewModel.cs

@@ -1,5 +1,6 @@
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
+using System.Runtime.ExceptionServices;
 
 namespace SimpleViewModel.BaseClasses;
 
@@ -9,6 +10,8 @@ namespace SimpleViewModel.BaseClasses;
 /// </summary>
 public class BaseViewModel : INotifyPropertyChanged
 {
+    private readonly SynchronizationContext? _syncContext = SynchronizationContext.Current;
+
     /// <inheritdoc/>
     public event PropertyChangedEventHandler? PropertyChanged;
 
@@ -21,9 +24,11 @@ public class BaseViewModel : INotifyPropertyChanged
     /// <param name="propertyName">The name of the property. This is optional and is automatically provided by the compiler.</param>
     protected void SetProperty<T>(ref T reference, T value, [CallerMemberName] string propertyName = "")
     {
-        if (Equals(reference, value)) return;
+        if (EqualityComparer<T>.Default.Equals(reference, value))
+            return;
+
         reference = value;
-        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        RaisePropertyChanged(propertyName);
     }
 
     /// <summary>
@@ -32,4 +37,27 @@ protected void SetProperty<T>(ref T reference, T value, [CallerMemberName] strin
     /// <param name="propertyName">The name of the property. This is optional and is automatically provided by the compiler.</param>
     protected virtual void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
         => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+
+    private void RaisePropertyChanged(string propertyName)
+    {
+        var handler = PropertyChanged;
+        if (handler is null)
+            return;
+
+        if (_syncContext != null)
+        {
+            _syncContext.Post(_ => handler(this, new(propertyName)), null);
+        }
+        else
+        {
+            handler(this, new(propertyName));
+        }
+    }
+
+    /// <summary>
+    /// Called when a generated command throws.
+    /// Default behavior preserves stack and crashes (correct for debugging).
+    /// Override in derived VMs for logging or UI reporting.
+    /// </summary>
+    public virtual void OnCommandException(Exception ex) => ExceptionDispatchInfo.Capture(ex).Throw();
 }

SimpleViewModel/SimpleViewModel.csproj

@@ -9,7 +9,7 @@
 
 	  <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
 	  <PackageId>SimpleViewModel</PackageId>
-	  <Version>0.9.7.4</Version>
+	  <Version>0.9.8.0</Version>
 	  <Authors>Derek Gooding</Authors>
 	  <Company>Derek Gooding</Company>
 	  <Description>

ViewModelGenerator/ViewModelGenerator.cs

@@ -100,6 +100,7 @@ public partial class {className} : BaseViewModel
                     var paramType = hasParameter ? method.Parameters[0].Type.ToDisplayString() : null;
 
                     // Generate command class per method
+                    var isAsync = IsAsyncTask(method);
                     var commandBuilder = new StringBuilder(
 $@"// <auto-generated />
 #nullable enable
@@ -116,20 +117,33 @@ public sealed class {commandClassName} : BaseCommand
             this.vm = vm;
         }}
 
-        public override void Execute(object? parameter)
+        public override {(isAsync ? "async void" : "void")} Execute(object? parameter)
         {{
 ");
+                    commandBuilder.AppendLine("            try");
+                    commandBuilder.AppendLine("            {");
+
                     if (acceptParameter && hasParameter)
                     {
-                        // Pass parameter to method
-                        commandBuilder.AppendLine($"            vm.{method.Name}(({paramType})parameter!);");
+                        if (isAsync)
+                            commandBuilder.AppendLine($"                await vm.{method.Name}(({paramType})parameter!);");
+                        else
+                            commandBuilder.AppendLine($"                vm.{method.Name}(({paramType})parameter!);");
                     }
                     else
                     {
-                        // Call parameterless method
-                        commandBuilder.AppendLine($"            vm.{method.Name}();");
+                        if (isAsync)
+                            commandBuilder.AppendLine($"                await vm.{method.Name}();");
+                        else
+                            commandBuilder.AppendLine($"                vm.{method.Name}();");
                     }
 
+                    commandBuilder.AppendLine("            }");
+                    commandBuilder.AppendLine("            catch (Exception ex)");
+                    commandBuilder.AppendLine("            {");
+                    commandBuilder.AppendLine("                vm.OnCommandException(ex);");
+                    commandBuilder.AppendLine("            }");
+
                     commandBuilder.AppendLine("        }");
                     var canExecute = GetCanExecuteMethodName(method);
                     if (!string.IsNullOrWhiteSpace(canExecute))
@@ -189,4 +203,18 @@ private static string ToPascal(string name)
         }
         return null;
     }
+
+    private static bool IsAsyncTask(IMethodSymbol method)
+    {
+        var returnType = method.ReturnType;
+
+        if (returnType is INamedTypeSymbol named)
+        {
+            if (named.Name == "Task" &&
+                named.ContainingNamespace.ToDisplayString() == "System.Threading.Tasks")
+                return true;
+        }
+
+        return false;
+    }
 }