Raise event several times while Mouse held down

Question

Basically let's say I'm making a simple counter, when I click the mouse, the counter goes up. My question is how do I program an even that makes it possible for me to have the counter flowing while the mouse I held down, basically something that works exactly as the KeyPress event handler, only with a mouse.

Answer 1

If you don't need a timer running for some other reason, I wouldn't use a timer. I would use a class property or global variable, depending on what you're doing.

private/public startTicks long = 0;

When you fire the MouseDown event:

startTicks = DateTime.Now.Ticks;

On the MouseUp event, take the difference and convert it to whatever time element (min, sec, hour) you want.

DoConversion(DateTime.Now.Ticks - startTicks);

Answer 2

I'm going to suggest a solution based on using Microsoft's Reactive Framework (Rx).

I've assumed that the MouseDown & MouseUp events are based on clicking the form and that there is a NumericUpDown control that we wish to increment every 0.1 seconds while the mouse is down.

Here's the Reactive Framework way of coding the solution:

var mouseDowns = Observable.FromEventPattern
    <MouseEventHandler, MouseEventArgs>(
        h => this.MouseDown += h,
        h => this.MouseDown -= h);

var mouseUps = Observable.FromEventPattern
    <MouseEventHandler, MouseEventArgs>(
        h => this.MouseUp += h,
        h => this.MouseUp -= h);

var intervals = Observable.Interval(TimeSpan.FromSeconds(0.1));

var query =
    from md in mouseDowns
    select intervals.TakeUntil(mouseUps);

query.Switch().ObserveOn(this).Subscribe(n => numericUpDown1.Value += 1);

The reactive query should be very easy to understand its purpose - basically it is "When you get a mouse down select the intervals until there is a mouse up."

The type of query is IObservable<IObservable<long>> so before the Subscribe we need to call Switch to turn the query into an IObservable<long>.

The ObserveOn(this) makes sure that the values of the observable are marshalled to the UI thread.

Rx can be a little tricky to learn, but once you've got it it is very powerful. I use it all the time.

Answer 3

Define a timer that starts firing its events when the MouseDown event occurs. Then set the MouseUp event to pause or stop the timer. Execute the code you want to be triggered when the timer elapses.