Reactive Extensions for .NET (Rx): Take action once all events are completed

Question

As a proof of concept, I want to write "Done" in a text box after a check box has been checked and a key has been pressed in a text box (in either order). I would expect this code to handle this, but it writes Done as soon as either event happens. Thanks for your help.

var seq = Observable.FromEvent<EventArgs>(this.checkBox, "CheckedChanged")
   .Merge(Observable.FromEvent<KeyPressEventArgs>(this.textBox, "KeyPress"));

seq.Subscribe((unused) => this.resultTextBox.Text = "Done");

Richard Anthony Hein · Accepted Answer · 2012-04-03T16:57:54.330

You can use Observable.When like so (I've added an additional CheckBox for this example):

var checkChanged  = Observable.FromEvent<EventArgs>(this.checkBox, "CheckedChanged");
var check1Changed = Observable.FromEvent<EventArgs>(this.checkBox1, "CheckedChanged");
var keyPress      = Observable.FromEvent<KeyPressEventArgs>(this.textBox, "KeyPress");

var plan1 = checkChanged
            .And(check1Changed).And(keyPress)
            .Then((cc, cc1, kp) => "Done.");

var when = Observable.When(plan1);

when.Subscribe((result) => this.resultTextBox.Text = result);

Also, if you can join other plans together, for example if things can be "done" when either one set of events fire, or also when another set of events fire:

var checkChanged  = Observable.FromEvent<EventArgs>(this.checkBox, "CheckedChanged");
var check1Changed = Observable.FromEvent<EventArgs>(this.checkBox1, "CheckedChanged");
var keyPress      = Observable.FromEvent<KeyPressEventArgs>(this.textBox, "KeyPress");
var keyPress1     = Observable.FromEvent<KeyPressEventArgs>(this.textBox1, "KeyPress");

var plan1 = checkChanged.And(check1Changed).And(keyPress).Then((cc, cc1, kp) => "Done.");
var plan2 = keyPress.And(keyPress1).Then((kp, kp1) => "Alternate done.");

var join = Observable.When(plan1, plan2);

Thanks - I toyed with this approach as well. If these events were async. network calls, would you prefer this style over the Zip approach? — Marcel Lamothe, Oct 06 '10 at 00:06
I like that. Is handling an error condition in one of these events a trivial matter? — Marcel Lamothe, Oct 06 '10 at 00:14
I haven't tried doing this with Zip, btw. Maybe I'll try it later to compare. — Richard Anthony Hein, Oct 06 '10 at 00:15
Handle errors via the Subscribe overload that takes an OnError Action. e.g.: join.Subscribe((result) => this.resultTextBox.Text = result, ex => Console.WriteLine("Error: {0}", ex.Message)); — Richard Anthony Hein, Oct 06 '10 at 00:15

score 1 · Answer 2 · answered Oct 05 '10 at 21:29

1

if you need both events to happen - consider using Zip. Merge will trigger the event if any of merged sources raise it.

answered Oct 05 '10 at 21:29

desco

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What if there were 10 different events, instead of two? – Marcel Lamothe Oct 05 '10 at 21:35
Zip returns Observable that will trigger events when both sources raise it (like rendezvous). You can Zip this result Observable with another one to obtain Observable connected to 3 sources etc... – desco Oct 05 '10 at 21:39
Would that be a reasonable approach? What about using Observable.Join with Ands? – Marcel Lamothe Oct 05 '10 at 22:05

Reactive Extensions for .NET (Rx): Take action once all events are completed

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