wpf - 错误无法在订阅 IObservable 时转换 lambda 表达式

Question

我正在尝试使用 Rx 在 wpf 中实现标准的拖放图像。

var mouseDown = from evt in Observable.FromEventPattern<MouseButtonEventArgs>(image, "MouseLeftButtonDown")
                          select evt.EventArgs.GetPosition(image);

            var mouseUp = Observable.FromEventPattern<MouseButtonEventArgs>(this, "MouseLeftButtonUp");

            var mouseMove = from evt in Observable.FromEventPattern<MouseEventArgs>(this, "MouseMove")
                            select evt.EventArgs.GetPosition(this);

            var q = from startLocation in mouseDown
                    from endLocation in mouseMove.TakeUntil(mouseUp)
                    select new Point 
                    {
                        X = endLocation.X - startLocation.X,
                        Y = endLocation.Y - startLocation.Y
                    };

            q.ObserveOn(SynchronizationContext.Current).Subscribe(point =>
            {
                Canvas.SetLeft(image, point.X);
                Canvas.SetTop(image, point.Y);
            });

我收到错误错误 Cannot convert lambda expression to type 'System.IObserver<System.Windows.Point>' because it is not a delegate type
我错过了什么？

Answer 1

命名空间 System.Reactive.Linq包含静态类 Observable它定义了常见响应式(Reactive)组合器的所有扩展方法。它位于 System.Reactive.dllIObservable<T>.Subscribe的扩展方法如 Subscribe(onNext) , Subscribe(onNext, onError)然而在 mscorlib 中定义在静态类中 System.ObservableExtensions .

tl;博士:

对于 Rx/Observable 扩展方法，您需要导入 System.Reactive.Linq = using System.Reactive.Linq;

对于订阅重载，您需要导入 System = using System;