Merge pull request #8905 from AvaloniaUI/fix-unpredictable-choice-between-methods-when-using-method-binding

Fix unpredictable choice between methods when using method binding.

src/Avalonia.Base/Data/Core/Plugins/MethodAccessorPlugin.cs

@@ -55,13 +55,20 @@ namespace Avalonia.Data.Core.Plugins
 
             var methods = type.GetMethods(bindingFlags);
 
-            foreach (MethodInfo methodInfo in methods)
+            foreach (var methodInfo in methods)
             {
                 if (methodInfo.Name == methodName)
                 {
-                    found = methodInfo;
+                    var parameters = methodInfo.GetParameters();
-
+                    if (parameters.Length == 1 && parameters[0].ParameterType == typeof(object))
-                    break;
+                    {
+                        found = methodInfo;
+                        break;
+                    }
+                    else if (parameters.Length == 0)
+                    {
+                        found = methodInfo;
+                    }
                 }
             }
 

tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_Method.cs

@@ -19,12 +19,9 @@ namespace Avalonia.Markup.UnitTests.Parsers
 
             public int MethodWithReturn() => 0;
 
-            public int MethodWithReturnAndParameters(int i) => i;
+            public int MethodWithReturnAndParameter(object i) => (int)i;
 
             public static void StaticMethod() { }
-
-            public static void ManyParameters(int a1, int a2, int a3, int a4, int a5, int a6, int a7, int a8, int a9) { }
-            public static int ManyParametersWithReturnType(int a1, int a2, int a3, int a4, int a5, int a6, int a7, int a8) => 1;
         }
 
         [Fact]
@@ -42,10 +39,8 @@ namespace Avalonia.Markup.UnitTests.Parsers
         [Theory]
         [InlineData(nameof(TestObject.MethodWithoutReturn), typeof(Action))]
         [InlineData(nameof(TestObject.MethodWithReturn), typeof(Func<int>))]
-        [InlineData(nameof(TestObject.MethodWithReturnAndParameters), typeof(Func<int, int>))]
+        [InlineData(nameof(TestObject.MethodWithReturnAndParameter), typeof(Func<object, int>))]
         [InlineData(nameof(TestObject.StaticMethod), typeof(Action))]
-        [InlineData(nameof(TestObject.ManyParameters), typeof(Action<int, int, int, int, int, int, int, int, int>))]
-        [InlineData(nameof(TestObject.ManyParametersWithReturnType), typeof(Func<int, int, int, int, int, int, int, int, int>))]
         public async Task Should_Get_Method_WithCorrectDelegateType(string methodName, Type expectedType)
         {
             var data = new TestObject();
@@ -61,10 +56,10 @@ namespace Avalonia.Markup.UnitTests.Parsers
         public async Task Can_Call_Method_Returned_From_Observer()
         {
             var data = new TestObject();
-            var observer = ExpressionObserverBuilder.Build(data, nameof(TestObject.MethodWithReturnAndParameters));
+            var observer = ExpressionObserverBuilder.Build(data, nameof(TestObject.MethodWithReturnAndParameter));
             var result = await observer.Take(1);
 
-            var callback = (Func<int, int>)result;
+            var callback = (Func<object, int>)result;
 
             Assert.Equal(1, callback(1));
 

tests/Avalonia.Markup.Xaml.UnitTests/Data/BindingTests_Method.cs

@@ -141,6 +141,28 @@ namespace Avalonia.Markup.Xaml.UnitTests.Data
             }
         }
 
+        [Fact]
+        public void Binding_Method_Preserves_Correct_Order()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.Xaml;assembly=Avalonia.Markup.Xaml.UnitTests'>
+    <Button Name='button' Command='{Binding Method3}' CommandParameter='5'/>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var button = window.FindControl<Button>("button");
+                var vm = new ViewModel();
+
+                button.DataContext = vm;
+                window.ApplyTemplate();
+                PerformClick(button);
+                Assert.Equal("Called Method with parameter of object type. Argument value is 5", vm.Value);
+            }
+        }
+
         [Fact]
         public void Binding_Method_To_Command_Collected()
         {
@@ -198,8 +220,10 @@ namespace Avalonia.Markup.Xaml.UnitTests.Data
             public event PropertyChangedEventHandler PropertyChanged;
 
             public string Method() => Value = "Called";
-            public string Method1(int i) => Value = $"Called {i}";
+            public string Method1(object i) => Value = $"Called {i}";
             public string Method2(int i, int j) => Value = $"Called {i},{j}";
+            public string Method3() => Value = "Called";
+            public string Method3(object obj) => Value = $"Called Method with parameter of object type. Argument value is {obj}";
             public string Value { get; private set; } = "Not called";
 
             object _parameter;