Merge pull request #4095 from workgroupengineering/features/Binding_Method_CanExecute

[Feature] binding method allow support can execute

samples/BindingDemo/MainWindow.xaml

@@ -116,6 +116,7 @@
         <RadioButton Content="Radio Button" IsChecked="{Binding !!BooleanFlag, Mode=OneWay}" Command="{Binding StringValueCommand}" CommandParameter="RadioButton"/>
         <TextBox Text="{Binding Path=StringValue}"/>
         <Button Content="Nested View Model Button" Name="NestedTest" Command="{Binding NestedModel.Command}" />
+        <Button Content="Command Method Do" Command="{Binding Do}" x:Name="ToDo"/>
       </StackPanel>
     </TabItem>
   </TabControl>

samples/BindingDemo/ViewModels/MainWindowViewModel.cs

@@ -7,6 +7,7 @@ using System.Threading.Tasks;
 using System.Threading;
 using ReactiveUI;
 using Avalonia.Controls;
+using Avalonia.Metadata;
 
 namespace BindingDemo.ViewModels
 {
@@ -102,5 +103,16 @@ namespace BindingDemo.ViewModels
             get { return _nested; }
             private set { this.RaiseAndSetIfChanged(ref _nested, value); }
         }
+
+        public void Do(object parameter)
+        {
+
+        }
+
+        [DependsOn(nameof(BooleanFlag))]
+        bool CanDo(object parameter)
+        {
+            return BooleanFlag;
+        }
     }
 }

src/Avalonia.Base/Data/Converters/AlwaysEnabledDelegateCommand.cs

@@ -1,41 +0,0 @@
-using System;
-using System.Globalization;
-using System.Reflection;
-using System.Windows.Input;
-using Avalonia.Utilities;
-
-namespace Avalonia.Data.Converters
-{
-    class AlwaysEnabledDelegateCommand : ICommand
-    {
-        private readonly Delegate action;
-
-        private ParameterInfo parameterInfo;
-
-        public AlwaysEnabledDelegateCommand(Delegate action)
-        {
-            this.action = action;
-            var parameters = action.Method.GetParameters();
-            parameterInfo = parameters.Length == 0 ? null : parameters[0];
-        }
-
-#pragma warning disable 0067
-        public event EventHandler CanExecuteChanged;
-#pragma warning restore 0067
-
-        public bool CanExecute(object parameter) => true;
-
-        public void Execute(object parameter)
-        {
-            if (parameterInfo == null)
-            {
-                action.DynamicInvoke();
-            }
-            else
-            {
-                TypeUtilities.TryConvert(parameterInfo.ParameterType, parameter, CultureInfo.CurrentCulture, out object convertedParameter);
-                action.DynamicInvoke(convertedParameter); 
-            }
-        }
-    }
-}

src/Avalonia.Base/Data/Converters/DefaultValueConverter.cs

@@ -33,7 +33,7 @@ namespace Avalonia.Data.Converters
 
             if (typeof(ICommand).IsAssignableFrom(targetType) && value is Delegate d && d.Method.GetParameters().Length <= 1)
             {
-                return new AlwaysEnabledDelegateCommand(d);
+                return new MethodToCommandConverter(d);
             }
 
             if (TypeUtilities.TryConvert(targetType, value, culture, out object result))

src/Avalonia.Base/Data/Converters/MethodToCommandConverter.cs

@@ -0,0 +1,230 @@
+using System;
+using System.ComponentModel;
+using System.Globalization;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Reflection;
+using System.Windows.Input;
+using Avalonia.Utilities;
+
+namespace Avalonia.Data.Converters
+{
+    class MethodToCommandConverter : ICommand
+    {
+        readonly static Func<object, bool> AlwaysEnabled = (_) => true;
+        readonly static MethodInfo tryConvert = typeof(TypeUtilities)
+            .GetMethod(nameof(TypeUtilities.TryConvert), BindingFlags.Public | BindingFlags.Static);
+        readonly static PropertyInfo currentCulture = typeof(CultureInfo)
+            .GetProperty(nameof(CultureInfo.CurrentCulture), BindingFlags.Public | BindingFlags.Static);
+        readonly Func<object, bool> canExecute;
+        readonly Action<object> execute;
+        readonly WeakPropertyChangedProxy weakPropertyChanged;
+        readonly PropertyChangedEventHandler propertyChangedEventHandler;
+        readonly string[] dependencyProperties;
+
+        public MethodToCommandConverter(Delegate action)
+        {
+            var target = action.Target;
+            var canExecuteMethodName = "Can" + action.Method.Name;
+            var parameters = action.Method.GetParameters();
+            var parameterInfo = parameters.Length == 0 ? null : parameters[0].ParameterType;
+
+            if (parameterInfo == null)
+            {
+                execute = CreateExecute(target, action.Method);
+            }
+            else
+            {
+                execute = CreateExecute(target, action.Method, parameterInfo);
+            }
+
+            var canExecuteMethod = action.Method.DeclaringType.GetRuntimeMethods()
+                .FirstOrDefault(m => m.Name == canExecuteMethodName
+                    && m.GetParameters().Length == 1
+                    && m.GetParameters()[0].ParameterType == typeof(object));
+            if (canExecuteMethod == null)
+            {
+                canExecute = AlwaysEnabled;
+            }
+            else
+            {
+                canExecute = CreateCanExecute(target, canExecuteMethod);
+                dependencyProperties = canExecuteMethod
+                    .GetCustomAttributes(typeof(Metadata.DependsOnAttribute), true)
+                    .OfType<Metadata.DependsOnAttribute>()
+                    .Select(x => x.Name)
+                    .ToArray();
+                if (dependencyProperties.Any()
+                    && target is INotifyPropertyChanged inpc)
+                {
+                    propertyChangedEventHandler = OnPropertyChanged;
+                    weakPropertyChanged = new WeakPropertyChangedProxy(inpc, propertyChangedEventHandler);
+                }
+            }
+        }
+
+        void OnPropertyChanged(object sender,PropertyChangedEventArgs args)
+        {
+            if (string.IsNullOrWhiteSpace(args.PropertyName)
+                               || dependencyProperties?.Contains(args.PropertyName) == true)
+            {
+                Threading.Dispatcher.UIThread.Post(() => CanExecuteChanged?.Invoke(this, EventArgs.Empty)
+                    , Threading.DispatcherPriority.Input);
+            }
+        }
+
+#pragma warning disable 0067
+        public event EventHandler CanExecuteChanged;
+#pragma warning restore 0067
+
+        public bool CanExecute(object parameter) => canExecute(parameter);
+
+        public void Execute(object parameter) => execute(parameter);
+
+
+        static Action<object> CreateExecute(object target
+            , System.Reflection.MethodInfo method)
+        {
+
+            var parameter = Expression.Parameter(typeof(object), "parameter");
+
+            var instance = Expression.Convert
+            (
+                Expression.Constant(target),
+                method.DeclaringType
+            );
+
+
+            var call = Expression.Call
+            (
+                instance,
+                method
+            );
+
+
+            return Expression
+                .Lambda<Action<object>>(call, parameter)
+                .Compile();
+        }
+
+        static Action<object> CreateExecute(object target
+            , System.Reflection.MethodInfo method
+            , Type parameterType)
+        {
+
+            var parameter = Expression.Parameter(typeof(object), "parameter");
+
+            var instance = Expression.Convert
+            (
+                Expression.Constant(target),
+                method.DeclaringType
+            );
+
+            Expression body;
+
+            if (parameterType == typeof(object))
+            {
+                body = Expression.Call(instance,
+                    method,
+                    parameter
+                    );
+            }
+            else
+            {
+                var arg0 = Expression.Variable(typeof(object), "argX");
+                var convertCall = Expression.Call(tryConvert,
+                     Expression.Constant(parameterType),
+                     parameter,
+                      Expression.Property(null, currentCulture),
+                     arg0
+                    );
+
+                var call = Expression.Call(instance,
+                    method,
+                    Expression.Convert(arg0, parameterType)
+                    );
+                body = Expression.Block(new[] { arg0 },
+                    convertCall,
+                    call
+                    );
+
+            }
+            Action<object> action = null;
+            try
+            {
+                action = Expression
+                   .Lambda<Action<object>>(body, parameter)
+                   .Compile();
+            }
+            catch (Exception ex)
+            {
+                throw ex;
+            }
+            return action;
+        }
+
+        static Func<object, bool> CreateCanExecute(object target
+            , System.Reflection.MethodInfo method)
+        {
+            var parameter = Expression.Parameter(typeof(object), "parameter");
+            var instance = Expression.Convert
+            (
+                Expression.Constant(target),
+                method.DeclaringType
+            );
+            var call = Expression.Call
+            (
+                instance,
+                method,
+                parameter
+            );
+            return Expression
+                .Lambda<Func<object, bool>>(call, parameter)
+                .Compile();
+        }
+
+
+        internal class WeakPropertyChangedProxy
+        {
+            readonly WeakReference<PropertyChangedEventHandler> _listener = new WeakReference<PropertyChangedEventHandler>(null);
+            readonly PropertyChangedEventHandler _handler;
+            internal WeakReference<INotifyPropertyChanged> Source { get; } = new WeakReference<INotifyPropertyChanged>(null);
+
+            public WeakPropertyChangedProxy()
+            {
+                _handler = new PropertyChangedEventHandler(OnPropertyChanged);
+            }
+
+            public WeakPropertyChangedProxy(INotifyPropertyChanged source, PropertyChangedEventHandler listener) : this()
+            {
+                SubscribeTo(source, listener);
+            }
+
+            public void SubscribeTo(INotifyPropertyChanged source, PropertyChangedEventHandler listener)
+            {
+                source.PropertyChanged += _handler;
+
+                Source.SetTarget(source);
+                _listener.SetTarget(listener);
+            }
+
+            public void Unsubscribe()
+            {
+                if (Source.TryGetTarget(out INotifyPropertyChanged source) && source != null)
+                    source.PropertyChanged -= _handler;
+
+                Source.SetTarget(null);
+                _listener.SetTarget(null);
+            }
+
+            void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
+            {
+                if (_listener.TryGetTarget(out var handler) && handler != null)
+                    handler(sender, e);
+                else
+                    Unsubscribe();
+            }
+           
+        }
+    }
+}

src/Avalonia.Base/Metadata/DependsOnAttribute.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Metadata
     /// <summary>
     /// Indicates that the property depends on the value of another property in markup.
     /// </summary>
-    [AttributeUsage(AttributeTargets.Property)]
+    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Method, Inherited = true, AllowMultiple = true)]
     public class DependsOnAttribute : Attribute
     {
         /// <summary>

src/Avalonia.Base/Properties/AssemblyInfo.cs

@@ -9,3 +9,4 @@ using Avalonia.Metadata;
 [assembly: InternalsVisibleTo("Avalonia.UnitTests")]
 [assembly: InternalsVisibleTo("DynamicProxyGenAssembly2")]
 [assembly: InternalsVisibleTo("Avalonia.Controls.DataGrid")]
+[assembly: InternalsVisibleTo("Avalonia.Markup.Xaml.UnitTests")]

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

@@ -1,5 +1,5 @@
-using System.Reactive.Subjects;
-using System.Windows.Input;
+using System;
+using System.ComponentModel;
 using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.UnitTests;
@@ -56,7 +56,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.Data
                 Assert.Equal("Called 5", vm.Value);
             }
         }
-        
+
         [Fact]
         public void Binding_Method_To_TextBlock_Text_Works()
         {
@@ -79,6 +79,111 @@ namespace Avalonia.Markup.Xaml.UnitTests.Data
             }
         }
 
+
+        [Theory]
+        [InlineData(null, "Not called")]
+        [InlineData("A", "Do A")]
+        public void Binding_Method_With_Parameter_To_Command_CanExecute(object commandParameter, string result)
+        {
+            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 Do}' CommandParameter='{Binding Parameter, Mode=OneTime}'/>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var button = window.FindControl<Button>("button");
+                var vm = new ViewModel()
+                {
+                    Parameter = commandParameter
+                };
+
+                button.DataContext = vm;
+                window.ApplyTemplate();
+
+                Assert.NotNull(button.Command);
+                PerformClick(button);
+                Assert.Equal(vm.Value, result);
+            }
+        }
+
+        [Fact]
+        public void Binding_Method_With_Parameter_To_Command_CanExecute_DependsOn()
+        {
+            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 Do}' CommandParameter='{Binding Parameter, Mode=OneWay}'/>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var button = window.FindControl<Button>("button");
+                var vm = new ViewModel()
+                {
+                    Parameter = null,
+                };
+
+                button.DataContext = vm;
+                window.ApplyTemplate();
+
+                Assert.NotNull(button.Command);
+
+                Assert.Equal(button.IsEffectivelyEnabled, false);
+
+                vm.Parameter = true;
+                Threading.Dispatcher.UIThread.RunJobs();
+
+                Assert.Equal(button.IsEffectivelyEnabled, true);
+            }
+        }
+
+        [Fact]
+        public void Binding_Method_To_Command_Collected()
+        {
+            WeakReference<ViewModel> MakeRef()
+            {
+                var weakVm = new WeakReference<ViewModel>(null);
+                {
+                    var vm = new ViewModel()
+                    {
+                        Parameter = null,
+                    };
+                    weakVm.SetTarget(vm);
+                    var canExecuteCount = 0;
+                    var action = new Action<object>(vm.Do);
+                    var command = new Avalonia.Data.Converters.MethodToCommandConverter(action);
+                    command.CanExecuteChanged += (s, e) => canExecuteCount++;
+                    vm.Parameter = 0;
+                    Threading.Dispatcher.UIThread.RunJobs();
+                    vm.Parameter = null;
+                    Threading.Dispatcher.UIThread.RunJobs();
+                    Assert.Equal(2, canExecuteCount);
+                }
+                return weakVm;
+            }
+            bool IsAlive(WeakReference<ViewModel> @ref)
+            {
+                return @ref.TryGetTarget(out var instance)
+                    && instance is null == false;
+            }
+
+            var vmref = MakeRef();
+
+            var beforeCollect = IsAlive(vmref);
+
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
+
+            var afterCollect = IsAlive(vmref);
+
+            Assert.True(beforeCollect, "Invalid ViewModel instance, it is already collected.");
+            Assert.False(afterCollect, "ViewModel instance was not collected");
+        }
+
         static void PerformClick(Button button)
         {
             button.RaiseEvent(new KeyEventArgs
@@ -88,12 +193,43 @@ namespace Avalonia.Markup.Xaml.UnitTests.Data
             });
         }
 
-        private class ViewModel
+        private class ViewModel : INotifyPropertyChanged
         {
+            public event PropertyChangedEventHandler PropertyChanged;
+
             public string Method() => Value = "Called";
             public string Method1(int i) => Value = $"Called {i}";
             public string Method2(int i, int j) => Value = $"Called {i},{j}";
             public string Value { get; private set; } = "Not called";
+
+            object _parameter;
+            public object Parameter
+            {
+                get
+                {
+                    return _parameter;
+                }
+                set
+                {
+                    if (_parameter == value)
+                    {
+                        return;
+                    }
+                    _parameter = value;
+                    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Parameter)));
+                }
+            }
+
+            public void Do(object parameter)
+            {
+                Value = $"Do {parameter}";
+            }
+
+            [Metadata.DependsOn(nameof(Parameter))]
+            public bool CanDo(object parameter)
+            {
+                return ReferenceEquals(null, parameter) == false;
+            }
         }
     }
 }