【UWP】使用Action代替Command

在Xaml中，说到绑定，我们用的最多的应该就是ICommand了，通过Command实现ViewModel到View之间的命令处理，例如Button默认就提供了Command支持，如下

Xaml：

    <Button Content="TestWithCommand" Command="{Binding TestCommand}" />

ViewModel

    /// <summary>Provides a base implementation of the <see cref="ICommand"/> interface. </summary>
    public abstract class CommandBase : ICommand
    {
        /// <summary>Gets a value indicating whether the command can execute in its current state. </summary>
        public abstract bool CanExecute { get; }

        /// <summary>Defines the method to be called when the command is invoked. </summary>
        protected abstract void Execute();

        /// <summary>Tries to execute the command by checking the <see cref="CanExecute"/> property 
        /// and executes the command only when it can be executed. </summary>
        /// <returns>True if command has been executed; false otherwise. </returns>
        public bool TryExecute()
        {
            if (!CanExecute)
                return false;
            Execute();
            return true;
        }

        /// <summary>Occurs when changes occur that affect whether or not the command should execute. </summary>
        public event EventHandler CanExecuteChanged;

        void ICommand.Execute(object parameter)
        {
            Execute();
        }

        bool ICommand.CanExecute(object parameter)
        {
            return CanExecute;
        }
    }

    /// <summary>Provides an implementation of the <see cref="ICommand"/> interface. </summary>
    public class RelayCommand : CommandBase
    {
        private readonly Action _execute;
        private readonly Func<bool> _canExecute;

        /// <summary>Initializes a new instance of the <see cref="RelayCommand"/> class. </summary>
        /// <param name="execute">The action to execute. </param>
        public RelayCommand(Action execute)
            : this(execute, null)
        { }

        /// <summary>Initializes a new instance of the <see cref="RelayCommand"/> class. </summary>
        /// <param name="execute">The action to execute. </param>
        /// <param name="canExecute">The predicate to check whether the function can be executed. </param>
        public RelayCommand(Action execute, Func<bool> canExecute)
        {
            if (execute == null)
                throw new ArgumentNullException(nameof(execute));

            _execute = execute;
            _canExecute = canExecute;
        }

        /// <summary>Defines the method to be called when the command is invoked. </summary>
        protected override void Execute()
        {
            _execute();
        }

        /// <summary>Gets a value indicating whether the command can execute in its current state. </summary>
        public override bool CanExecute => _canExecute == null || _canExecute();
    }

    public class MainPageViewModel
    {
        public ICommand TestCommand { get; private set; }
        public MainPageViewModel()
        {
            TestCommand = new RelayCommand(TestCmd);
        }

        public void TestCmd()
        {
            Debug.WriteLine("TestCmd");
        }
    }

上面只是一个最简单的例子，但是如果需要绑定的方法很多的时候，就会有一大堆的ICommand属性定义，并且也需要初始化，代码看起来特别臃肿

下面我们使用Behavior代替Command完成方法的绑定

在WinRT中，Behavior是以组件的方法安装到VS上的，而在UWP上，官方并没有提供对应的组件，我们可以通过Nuget添加UWP版本的Behavior组件：

　　http://www.nuget.org/packages/Microsoft.Xaml.Behaviors.Uwp.Managed/

使用如下

Xaml

    <Button Content="TestWithAction">
        <interactivity:Interaction.Behaviors>
            <core:EventTriggerBehavior EventName="Click">
                <core:CallMethodAction TargetObject="{Binding}" MethodName="Test"/>
            </core:EventTriggerBehavior>
        </interactivity:Interaction.Behaviors>
    </Button>

ViewModel

    public class MainPageViewModel
    {
        public void Test()
        {
            Debug.WriteLine("test");
        }
    }

　　官方提供的Behavior更加灵活，可以自己配置事件名，和对应的方法名称，并且我们在ViewModel中不需要写ICommand等代码了，看起来更简洁明了，但是还有个问题，

有时候我们需要用到事件的参数，有时候我们需要用到触发事件的控件，有时候我们还需要控件对应的DataContext，而官方提供的库中并不提供带参数的方法，下面我们对其进行修改一下，让其支持参数传递，并且支持多参数

自定义一个支持参数Action

    public class Parameter : DependencyObject
    {
        public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
            "Value", typeof (object), typeof (Parameter), new PropertyMetadata(default(object)));

        public object Value
        {
            get { return (object) GetValue(ValueProperty); }
            set { SetValue(ValueProperty, value); }
        }
    }

    /// <summary>
    /// 带参数的Action
    /// </summary>
    [ContentProperty(Name = "Parameters")]
    public sealed class WdCallMethodAction : DependencyObject, IAction
    {
        public static readonly DependencyProperty MethodNameProperty = DependencyProperty.Register("MethodName",
            typeof (string), typeof (WdCallMethodAction), new PropertyMetadata(null));

        public static readonly DependencyProperty TargetObjectProperty = DependencyProperty.Register("TargetObject",
            typeof (object), typeof (WdCallMethodAction), new PropertyMetadata(null));

        public static readonly DependencyProperty ParametersProperty = DependencyProperty.Register(
            "Parameters", typeof (ICollection<Parameter>), typeof (WdCallMethodAction),
            new PropertyMetadata(new List<Parameter>()));
        
        /// <summary>
        /// 方法名：参数有?,eventArgs,sender,dataContext
        ///     eg：Test
        ///     eg：Test(?,?)
        ///     eg：Test(sender,?,?)
        /// </summary>
        public string MethodName
        {
            get { return (string) GetValue(MethodNameProperty); }
            set { SetValue(MethodNameProperty, value); }
        }

        public ICollection<Parameter> Parameters
        {
            get { return (ICollection<Parameter>) GetValue(ParametersProperty); }
            set { SetValue(ParametersProperty, value); }
        }

        public object TargetObject
        {
            get { return GetValue(TargetObjectProperty); }
            set { SetValue(TargetObjectProperty, value); }
        }

        public object Execute(object sender, object parameter)
        {
            InvokeMethod(MethodName, sender, parameter, TargetObject, Parameters);
            return true;
        }

        public void InvokeMethod(string methodName, object sender, object eventArgs, object dataContext,
            ICollection<Parameter> parameters)
        {
            var start = methodName.IndexOf('(');
            var end = methodName.IndexOf(')');

            MethodInfo methodInfo;

            if (start >= 0 && end >= 0)
            {
                var paras = methodName.Substring(start + 1, end - start - 1)
                    .Split(new[] {',', ' '}, StringSplitOptions.RemoveEmptyEntries);

                methodName = MethodName.Substring(0, start);

                var allParameter = new List<object>();
                var enumerator = parameters.GetEnumerator();
                foreach (var para in paras)
                {
                    switch (para)
                    {
                        case "?":
                            enumerator.MoveNext();
                            allParameter.Add(enumerator.Current);
                            break;
                        case "eventArgs":
                            allParameter.Add(eventArgs);
                            break;
                        case "sender":
                            allParameter.Add(sender);
                            break;
                        case "dataContext":
                            allParameter.Add(dataContext);
                            break;
                        default:
                            throw new NotImplementedException(string.Format("没有实现该参数:{0}", para));

                    }
                }

                var paramCount = paras.Length;
                methodInfo = TargetObject.GetType().GetRuntimeMethods()
                    .FirstOrDefault(m => Equals(m.Name, methodName) && m.GetParameters().Count() == paramCount);

                methodInfo.Invoke(TargetObject, allParameter.ToArray());
            }
            else
            {
                methodInfo = TargetObject.GetType().GetRuntimeMethod(methodName, new Type[0]);
                methodInfo.Invoke(TargetObject, null);
            }

        }
    }

Xaml

    <Button x:Name="btn" Content="TestWithActionAndParameter">
        <interactivity:Interaction.Behaviors>
            <core:EventTriggerBehavior EventName="Click">
                <command:WdCallMethodAction TargetObject="{Binding}" MethodName="Test(eventArgs, sender, dataContext, ?,?)">
                    <command:Parameter Value="32"/>
                    <!-- 参数暂不支持绑定（下面方式为空）-->
                    <command:Parameter Value="{Binding ElementName=btn}"/>
                </command:WdCallMethodAction>
            </core:EventTriggerBehavior>
        </interactivity:Interaction.Behaviors>
    </Button>

ViewModel

    public void Test(RoutedEventArgs eventArgs, FrameworkElement sender, MainPageViewModel dataContext, Parameter param1, object param2)
    {
        Debug.WriteLine("sender:{0}", sender);
        Debug.WriteLine("eventArgs:{0}", eventArgs);
        Debug.WriteLine("dataContext:{0}", dataContext);
        Debug.WriteLine("param1:{0}", param1);
        Debug.WriteLine("param2:{0}", param2);
    }

注：目前Parameter暂不支持绑定

 demo

　　http://files.cnblogs.com/files/bomo/CommandInvokeDemo.zip