Question

我正在努力处理拖累和丢弃交互，包括鼠标按下，鼠标移动和鼠标移动。

以下是我的解决方案的简化版本：

在鼠标按下时，创建一个椭圆并将其添加到画布
在鼠标移动时，重新定位椭圆以跟随鼠标

，更改画布的颜色，以便明显拖动哪一个。

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就是

    <Canvas x:Name="canvas"/>

有一些我不喜欢这个代码的东西，我需要帮助重构它：）

首先：mousedown和mouseup回调被指定为副作用。如果对q进行了两次订阅，则会发生两次订阅。

其次，在 mousemove回调之前指定了鼠标回调。这使得它有点难以阅读。

第三，对椭圆的引用似乎是在一个愚蠢的地方。如果有两个订阅，则该变量引用将很快被覆盖。我确信应该有一些方法可以利用let关键字向linq表达式引入一个变量，这意味着鼠标移动和鼠标移动处理程序都可以使用正确的椭圆引用

你会怎么写这段代码？

Answer 1

为了避免产生副作用，您应该发布您的observable。我认为这样的事情会好的：

        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();
    }

构建Linq-to-Events Drag的最佳方法是什么？删除代码？

1 个答案: