什么是最好的方式结构，这个皇宫-对-事拖拉的代码？

Question

我试图处理一个拖拉的互动，其中涉及老鼠下，老鼠移动和鼠标。

这里是一个简化的重现我的解决方案：

• 在鼠下，创建一个椭圆，并将它添加到画布
• 在老鼠移动，重新定位椭圆遵循鼠

• 在鼠，改变颜色的画布所以，这是显而易见的是哪一个你拖动。

  var mouseDown = Observable.FromEvent<MouseButtonEventArgs>(canvas, "MouseLeftButtonDown");
  var mouseUp = Observable.FromEvent<MouseButtonEventArgs>(canvas, "MouseLeftButtonUp");
  var mouseMove = Observable.FromEvent<MouseEventArgs>(canvas, "MouseMove");
  
  Ellipse ellipse = null;
  
  var q = from start in mouseDown.Do(x =>
              {
                  // handle mousedown by creating a red ellipse, 
                  // adding it to the canvas at the right position
                  ellipse = new Ellipse() { Width = 10, Height = 10, Fill = Brushes.Red };
                  Point position = x.EventArgs.GetPosition(canvas);
                  Canvas.SetLeft(ellipse, position.X);
                  Canvas.SetTop(ellipse, position.Y);
                  canvas.Children.Add(ellipse);
              })
          from delta in mouseMove.Until(mouseUp.Do(x =>
              {
                  // handle mouse up by making the ellipse green
                  ellipse.Fill = Brushes.Green;
              }))
          select delta;
  
  q.Subscribe(x =>
  {
      // handle mouse move by repositioning ellipse
      Point position = x.EventArgs.GetPosition(canvas);
      Canvas.SetLeft(ellipse, position.X);
      Canvas.SetTop(ellipse, position.Y);
  });
  

XAML是简单

    <Canvas x:Name="canvas"/>

有几件事情我不喜欢这个代码，我需要帮助的重构，它:)

首先：该mousedown和mouseup回被指定为副作用。如果两个订阅了 q, 他们会发生的两倍。

第二，mouseup回指定 之前 该鼠标移回调。这使得它有点难于阅读。

第三，参考椭圆似乎是在一个愚蠢的地方。如果有两个订阅，该变量的基准将得到复盖相当迅速。我敢肯定，应该有一些办法，我们可以利用 let 关键字来介绍一个变量来皇宫的表达，这将意味着正确的椭圆参考是提供给老鼠移动和老鼠了处理程序

你会怎么写这个代码?

Answer 1

为了避免subscrition的副作用，应发布观察。我认为这样的事情将是确定：

        public MainWindow()
    {
        InitializeComponent();
        var mouseDown = Observable
            .FromEvent<MouseButtonEventArgs>(this, "MouseLeftButtonDown");
        var mouseUp = Observable
            .FromEvent<MouseButtonEventArgs>(this, "MouseLeftButtonUp");
        var mouseMove = Observable
            .FromEvent<MouseEventArgs>(this, "MouseMove");

        var ellipses = mouseDown
            .Select(args => new { 
                a = args, 
                el = new Ellipse
                {
                    Width = 10, Height = 10, Fill = Brushes.Red
                }})
            .Publish();

        ellipses
            .Subscribe(elargs =>
            {
                var position = elargs.a.EventArgs.GetPosition(canvas);
                Canvas.SetLeft(elargs.el, position.X);
                Canvas.SetTop(elargs.el, position.Y);
                canvas.Children.Add(elargs.el);
            });

        var elmove = from elargs in ellipses
                     from mm in mouseMove.TakeUntil(mouseUp)
                     select new { a = mm, el = elargs.el };

        elmove.
            Subscribe(elargs =>
            {
                var position = elargs.a.EventArgs.GetPosition(canvas);
                Canvas.SetLeft(elargs.el, position.X);
                Canvas.SetTop(elargs.el, position.Y);
            });

        var elmup = from elargs in ellipses
                    from mup in mouseUp
                    select elargs.el;

        elmup.Subscribe(el => el.Fill = Brushes.Green);

        ellipses.Connect();
    }