当我开始思考如何将 MVVM 和 RX “结合”起来时，我首先想到的是一个 ObservableCommand：
public class ObservableCommand : ICommand, IObservable<object>
{
private readonly Subject<object> _subj = new Subject<object>();
public void Execute(object parameter)
{
_subj.OnNext(parameter);
}
public bool CanExecute(object parameter)
{
return true;
}
public event EventHandler CanExecuteChanged;
public IDisposable Subscribe(IObserver<object> observer)
{
return _subj.Subscribe(observer);
}
}
但后来我认为将控件绑定到 ICommand 属性的“标准”MVVM 方式不是很 RX'ish，它将事件流分解为相当静态的耦合。RX 更多的是关于事件，并且监听一个Executed路由事件似乎是合适的。这是我想出的：
1）你有一个命令中继行为，你安装在每个用户控件的根目录下，它应该响应命令：
public class CommandRelay : Behavior<FrameworkElement>
{
private ICommandSink _commandSink;
protected override void OnAttached()
{
base.OnAttached();
CommandManager.AddExecutedHandler(AssociatedObject, DoExecute);
CommandManager.AddCanExecuteHandler(AssociatedObject, GetCanExecute);
AssociatedObject.DataContextChanged
+= AssociatedObject_DataContextChanged;
}
protected override void OnDetaching()
{
base.OnDetaching();
CommandManager.RemoveExecutedHandler(AssociatedObject, DoExecute);
CommandManager.RemoveCanExecuteHandler(AssociatedObject, GetCanExecute);
AssociatedObject.DataContextChanged
-= AssociatedObject_DataContextChanged;
}
private static void GetCanExecute(object sender,
CanExecuteRoutedEventArgs e)
{
e.CanExecute = true;
}
private void DoExecute(object sender, ExecutedRoutedEventArgs e)
{
if (_commandSink != null)
_commandSink.Execute(e);
}
void AssociatedObject_DataContextChanged(
object sender, DependencyPropertyChangedEventArgs e)
{
_commandSink = e.NewValue as ICommandSink;
}
}
public interface ICommandSink
{
void Execute(ExecutedRoutedEventArgs args);
}
2）为用户控件服务的ViewModel继承自ReactiveViewModel：
public class ReactiveViewModel : INotifyPropertyChanged, ICommandSink
{
internal readonly Subject<ExecutedRoutedEventArgs> Commands;
public ReactiveViewModel()
{
Commands = new Subject<ExecutedRoutedEventArgs>();
}
...
public void Execute(ExecutedRoutedEventArgs args)
{
args.Handled = true; // to leave chance to handler
// to pass the event up
Commands.OnNext(args);
}
}
3）您不将控件绑定到 ICommand 属性，而是使用 RoutedCommand 的：
public static class MyCommands
{
private static readonly RoutedUICommand _testCommand
= new RoutedUICommand();
public static RoutedUICommand TestCommand
{ get { return _testCommand; } }
}
在 XAML 中：
<Button x:Name="btn" Content="Test" Command="ViewModel:MyCommands.TestCommand"/>
因此，在您的 ViewModel 上，您可以以非常 RX 的方式收听命令：
public MyVM() : ReactiveViewModel
{
Commands
.Where(p => p.Command == MyCommands.TestCommand)
.Subscribe(DoTestCommand);
Commands
.Where(p => p.Command == MyCommands.ChangeCommand)
.Subscribe(DoChangeCommand);
Commands.Subscribe(a => Console.WriteLine("command logged"));
}
现在，您拥有路由命令的强大功能（您可以自由选择在层次结构中的任何甚至多个 ViewModel 上处理命令），此外，您对所有命令都有一个“单一流程”，这比单独的 IObservable 对 RX 更好.