Add execution guards to the async version to prevent quick click errors.

Author: DerekGooding

SimpleViewModel/SimpleViewModel.csproj

@@ -9,7 +9,7 @@
 
 	  <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
 	  <PackageId>SimpleViewModel</PackageId>
-	  <Version>0.9.8.2</Version>
+	  <Version>0.9.8.3</Version>
 	  <Authors>Derek Gooding</Authors>
 	  <Company>Derek Gooding</Company>
 	  <Description>

ViewModelGenerator/ViewModelGenerator.cs

@@ -81,7 +81,6 @@ public partial class {className} : BaseViewModel
                         viewModelBuilder.AppendLine($"          {onChange}();");
                     viewModelBuilder.AppendLine("        }}");
                 }
-                //viewModelBuilder.AppendLine("    }"); // <-- FIX: close property
 
                 foreach (var method in commandMethods)
                 {
@@ -90,17 +89,16 @@ public partial class {className} : BaseViewModel
                     viewModelBuilder.AppendLine($"        private {commandClassName}? _{commandFieldName} {{ get; set; }}");
                     viewModelBuilder.AppendLine($"        public {commandClassName} {commandFieldName} => _{commandFieldName} ??= new(this);");
 
-                    // Check for AcceptParameter property on CommandAttribute
                     var acceptParameter = method.GetAttributes()
                         .FirstOrDefault(attr => attr.AttributeClass?.Name == "CommandAttribute")?
                         .NamedArguments.FirstOrDefault(arg => arg.Key == "AcceptParameter").Value.Value as bool? ?? false;
 
-                    // Check if method has a single parameter
                     var hasParameter = method.Parameters.Length == 1;
                     var paramType = hasParameter ? method.Parameters[0].Type.ToDisplayString() : null;
 
-                    // Generate command class per method
                     var isAsync = IsAsyncTask(method);
+                    var canExecute = GetCanExecuteMethodName(method);
+
                     var commandBuilder = new StringBuilder(
 $@"// <auto-generated />
 #nullable enable
@@ -111,15 +109,35 @@ namespace {namespaceName}
     public sealed class {commandClassName} : BaseCommand
     {{
         private readonly {className} vm;
+        private bool _isExecuting;
+");
+                    if (isAsync)
+                        commandBuilder.AppendLine("        private readonly SemaphoreSlim _executeLock = new(1, 1);");
 
-        public {commandClassName}({className} vm)
-        {{
-            this.vm = vm;
-        }}
+                    commandBuilder.AppendLine();
+                    commandBuilder.AppendLine($"        public {commandClassName}({className} vm)");
+                    commandBuilder.AppendLine("        {");
+                    commandBuilder.AppendLine("            this.vm = vm;");
+                    commandBuilder.AppendLine("        }");
+                    commandBuilder.AppendLine();
 
-        public override {(isAsync ? "async void" : "void")} Execute(object? parameter)
-        {{
-");
+                    if (!string.IsNullOrWhiteSpace(canExecute))
+                        commandBuilder.AppendLine($"        public override bool CanExecute(object? parameter) => !_isExecuting && vm.{canExecute}();");
+                    else
+                        commandBuilder.AppendLine("        public override bool CanExecute(object? parameter) => !_isExecuting;");
+
+                    commandBuilder.AppendLine();
+
+                    // Execute
+                    commandBuilder.AppendLine($"        public override {(isAsync ? "async void" : "void")} Execute(object? parameter)");
+                    commandBuilder.AppendLine("        {");
+                    commandBuilder.AppendLine("            if (_isExecuting) return;");
+
+                    if (isAsync)
+                        commandBuilder.AppendLine("            if (!_executeLock.Wait(0)) return;");
+
+                    commandBuilder.AppendLine("            _isExecuting = true;");
+                    commandBuilder.AppendLine("            RaiseCanExecuteChanged();");
                     commandBuilder.AppendLine("            try");
                     commandBuilder.AppendLine("            {");
 
@@ -143,13 +161,19 @@ public sealed class {commandClassName} : BaseCommand
                     commandBuilder.AppendLine("            {");
                     commandBuilder.AppendLine("                vm.OnCommandException(ex);");
                     commandBuilder.AppendLine("            }");
+                    commandBuilder.AppendLine("            finally");
+                    commandBuilder.AppendLine("            {");
+                    commandBuilder.AppendLine("                _isExecuting = false;");
+
+                    if (isAsync)
+                        commandBuilder.AppendLine("                _executeLock.Release();");
 
+                    commandBuilder.AppendLine("                RaiseCanExecuteChanged();");
+                    commandBuilder.AppendLine("            }");
                     commandBuilder.AppendLine("        }");
-                    var canExecute = GetCanExecuteMethodName(method);
-                    if (!string.IsNullOrWhiteSpace(canExecute))
-                        commandBuilder.AppendLine($"        public override bool CanExecute(object? parameter) => vm.{canExecute}();");
                     commandBuilder.AppendLine("    }");
                     commandBuilder.AppendLine("}");
+
                     spc.AddSource($"{commandClassName}.g.cs", SourceText.From(commandBuilder.ToString(), Encoding.UTF8));
                 }
 
@@ -177,9 +201,7 @@ private static string ToPascal(string name)
                 foreach (var namedArg in attr.NamedArguments)
                 {
                     if (namedArg.Key == "CanExecuteMethodName")
-                    {
                         return namedArg.Value.Value?.ToString();
-                    }
                 }
             }
         }
@@ -195,9 +217,7 @@ private static string ToPascal(string name)
                 foreach (var namedArg in attr.NamedArguments)
                 {
                     if (namedArg.Key == "OnChangeMethodName")
-                    {
                         return namedArg.Value.Value?.ToString();
-                    }
                 }
             }
         }
@@ -207,14 +227,7 @@ private static string ToPascal(string name)
     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;
+        return returnType is INamedTypeSymbol named && named.Name == "Task" &&
+               named.ContainingNamespace.ToDisplayString() == "System.Threading.Tasks";
     }
-}
+}