如何防止在按下鼠标按钮时发生mousemove事件？

Question

I got a grid that I want to move mouse over. While I am just hovering and moving mouse I want events to fire, but when I press mousedown they should pause firing. Once I fire mouseup they should continue.

If that sounds super easy, it probably isn't. After some time we came up with a not very elegant solution, but I wonder whether something better exists. I won't influence your approach with our hack.

So initial code that doesn't work

mouseMove.TakeUntil(mouseDown).Repeat()

Adding .SkipUntil(mouseUp) left or right to TakeUntil basicly stop above code from working at all.

Answer 1

How about this:

bool mouseIsDown = false;
Observable.Merge(
    mouseDown.Select(_ => true),
    mouseUp.Select(_ => false)
).Subscribe(x => mouseIsDown = x);

mouseMove.Where(_ => !mouseIsDown);

The technically correct answer involves the Window operator, but this is just as good and easier to grok (and easier for me to write)

Answer 2

this could be a posible solution

// create the observables
IObservable<Point> mouseMove = Observable.FromEventPattern<MouseEventArgs>(this, "MouseDown")
    .Select(e=>e.EventArgs.GetPosition(this));

IObservable<bool> mouseDown = Observable.FromEventPattern(this, "MouseDown").Select(_ => false);
IObservable<bool> mouseUp = Observable.FromEventPattern(this, "MouseUp").Select(_ => true);

var merged = mouseUp.Merge(mouseDown).StartWith(true);

// sends the moves with the current state of the mouse button
var all = mouseMove.CombineLatest(merged, (move, take) => new {Take = take, Move = move});

// the result is all the points from mouse move where the mouse button isn't pressed
var result = all.Where(t => t.Take).Select(t => t.Move);

Answer 3

Below are 2 possible solutions

var beh = new BehaviorSubject<bool>(true);
mousedown.Select(_ => false).Subscribe(beh);
mouseup.Select(_ => true).Subscribe(beh);
mousemove.SelectMany(e =>
{
     return mousemove.TakeUntil(beh.Where(b => !b));
}).Subscribe( .... );

OR

var du = mousedown.Select(_ => false).Merge(mouseup.Select(_ => true)).Merge(Observable.Return(true));
mousemove.CombineLatest(du, (ev, b) => new Tuple<MouseEventArgs, bool>(ev.EventArgs, b))
 .Where(t => t.Item2)
 .Select(t => t.Item1)
 .Subscribe(....);

Answer 4

This works:

        var mouseMoveWhileUpOnly =
            mouseUp
                .Select(mu =>
                    mouseMove
                        .TakeUntil(mouseDown))
                .Switch();

The only trick you need to do to get the observable started without actually needing to manually do a mouse up is this:

        var mouseUp = Observable
            .FromEventPattern<MouseButtonEventHandler, MouseButtonEventArgs>(
                h => this.MouseLeftButtonUp += h,
                h => this.MouseLeftButtonUp -= h)
            .Select(ep => Unit.Default)
            .StartWith(Unit.Default);

Note the StartWith .

Otherwise the mouseDown & mouseMove observables are defined normally.