用Reactive响应式框架实现Windows phone 7 MVVM 按钮Command绑定，列表子元素的Command绑定

1. Button 在WP7中似乎没有实现ICommand接口，为MVVM开发带来了一定的麻烦。 那么我怎么办呢？ 而微软System.Windows.Interactivity.dll 中的EventTrigger似乎有问题，我不知道网上很多用这个MVVMLight 是怎么实现没有抱错的。。。。。

WP7，Silverlight开发会涉及到很多的线程问题，而一般的开发很难控制线程之间出错异常的捕捉，线程及资源的释放。Reactive (Rx) 似乎是这方面天生的料。 所以我项目用到了MVVM框架ReactiveUI。大家可以在https://github.com/xpaulbettsx/ReactiveUI 这里找到。闲话不多说了。 怎么做Button的命令绑定呢？ 既然无路可走，那么我们就自己修路吧，实现ICommand的Button。上菜：

public class CommandButton : Button
    {
        #region Command Property

        public ICommand Command
        {
            get { return (ICommand)GetValue(CommandProperty); }
            set { SetValue(CommandProperty, value); }
        }

        public static readonly DependencyProperty CommandProperty=
            DependencyProperty.Register("Command",
            typeof(ICommand),
            typeof(CommandButton),
            new PropertyMetadata(OnCommandChanged));

        private static void OnCommandChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            ((CommandButton)obj).OnCommandChanged(e);
        }

        private void OnCommandChanged(DependencyPropertyChangedEventArgs e)
        {
            if (e.OldValue != null)
            {
                ICommand command = e.OldValue as ICommand;
                if (command != null)
                {
                    command.CanExecuteChanged -= CommandCanExecuteChanged;
                }
            }

            if (e.NewValue != null)
            {
                ICommand command = e.NewValue as ICommand;
                if (command != null)
                {
                    command.CanExecuteChanged += CommandCanExecuteChanged;
                }
            }

            UpdateIsEnabled();
        }

        #endregion

        #region CommandParameter Property

        public object CommandParameter
        {
            get { return (object)GetValue(CommandParameterProperty); }
            set { SetValue(CommandParameterProperty, value); }
        }

        public static readonly DependencyProperty CommandParameterProperty =
            DependencyProperty.Register("CommandParameter",
            typeof(object), 
            typeof(CommandButton),
            new PropertyMetadata(OnCommandParameterChanged));

        private static void OnCommandParameterChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            ((CommandButton)obj).UpdateIsEnabled();
        }

        #endregion


        private void CommandCanExecuteChanged(object sender, EventArgs e)
        {
            UpdateIsEnabled();
        }

        private void UpdateIsEnabled()
        {
            IsEnabled = Command != null ? Command.CanExecute(CommandParameter) : false;
        }

        protected override void OnClick()
        {
            base.OnClick();

            if (Command != null)
            {
                Command.Execute(CommandParameter);
            }
        }
    }

在给大家看看一个人员ViewModel 吧

/// <summary>
    /// this view model include user information.
    /// </summary>
    public abstract class AccountViewModelBase : ViewModelBase
    {
        private string _UserId;
        /// <summary>
        /// User's account id
        /// </summary>
        public string UserId
        {
            get { return _UserId; }
            set { this.RaiseAndSetIfChanged(x => x.UserId, ref _UserId, value); }
        }

        //private User _CurrentUser;
        //protected ObservableAsPropertyHelper<User> _CurrentUser;
        private User _user;
        public User CurrentUser
        {
            get
            {
                //if (_user != null)
                return _user;
                //return _CurrentUser.Value;
            }
            set { this.RaiseAndSetIfChanged(x => x.CurrentUser, ref _user, value); }
        }

        public ReactiveAsyncCommand GetUserCommand { get; private set; }

        public AccountViewModelBase(User user = null)
        {
            if (user != null)
            {
                _user = user;
                _UserId = user.Id;
            }

            GetUserCommand = new ReactiveAsyncCommand();
            this.ObservableForProperty(x => x.UserId)
                .Throttle(TimeSpan.FromMilliseconds(500))
                .Subscribe(x =>
                    {
                        _user = null;// if UserId change clear the loacl user.
                        GetUserCommand.Execute(x.Value);
                    });

           GetUserCommand.Subscribe(x => 
                OAuthHelper.CreateClient(OAuthHelper.USER_PROFILE_URL, new ParameterCollection { new Parameter("id", (string)x) })
                    .GetResponseText()
                    .Select(s => XElement.Parse(s))
                    .Select(xl => xl.ReadUserInfo())
                    .ObserveOn(RxApp.DeferredScheduler)
                    .Subscribe(
                        u => CurrentUser = u,
                        ex => { this.Log().Error(ex.ToString()); MessageBox.Show(ex.ToString()); }));

        }
    }

　　

这里只要UserId 的值变化，就能重新查询获得新的CurrentUser对象。 而且UserId是根据500微妙中变化的最后一个值为准来查询。

上面我的ViewModel可以更具值变化来触发GetUserCommand命令，所有可以不用绑定， 若果需要在Xaml上来触发呢，看看XMAL文件只需要这么绑定就好

<my1:CommandButton Command="{Binding GoBackCommand}" x:Name="btnHome" Grid.Column="2"

Style="{StaticResource ButtonStyle}" Margin="0,0,1,0" />

好了，时间差不多了，。。List列表的绑定需要用到RelativeSource Binding，Silverlight4 和 WP7都没有实现，

下一节我们再说说怎么自定义实现RelativeSource Binding吧休息。。。。