C# do some work after all events are raised (or combine events) -

i'd subscribe event raised when of multiple other events raised.

suppose have multiple tasks (a) first (for example animating multiple independent views), can subscribe event task complete, , i'd other work (b) after of these events finished.

the amount of first tasks (a) can differ each time, @ moment set counter number of tasks a, subscribe n events, , in event handler task completion decrement counter, , when it's zero, task b.

is there nicer way combine these events using counter?

if understand question correctly, increment counter when start tasks , when each task completed, decrement counter in event handler. in event handler, check see (after decrementing counter) if counter zero. if so, task b.

i suggest @ tasks (aka "task parallel library (tpl)"), allows this:

task.whenall( new task[] {     task.run(()=> { //... work a1... },     task.run(()=> { //... work a2... },     task.run(()=> { //... work a3... }})     .continuewith(()=> {//... work b... }); 

---

update: based on mention of wpf animations in comment below, task.run may not fit here. if remember correctly, completed event, , don't have way run animations synchronously in code (as in "...do work a1...").

however, instead of creating tasks via task.run, can create them completed event of storyboard via extension method like:

public static task<storyboard> beginasync(this storyboard sb) {    var tcs = new taskcompletionsource<storyboard>();    sb.completed += (s, a) => tcs.trysetresult(sb);    sb.begin();    return tcs.task; } 

note method creates task completed in storyboard's completed event handler, , begins storyboard animation before returning task. note can write similar extension method other types , events.

you'd use method like, example:

var sb1 = (storyboard)mainwindow.findresource("storyboard1"); var sb2 = (storyboard)mainwindow.findresource("storyboard2"); var sb3 = (storyboard)mainwindow.findresource("storyboard3");  task.whenall( new task[] {     sb1.beginasync(),     sb2.beginasync(),     sb3.beginasync() })     .continuewith(() => messagebox.show("all done!"),         taskscheduler.fromcurrentsynchronizationcontext()); 

taskscheduler.fromcurrentsynchronizationcontext() schedules continuation task run on ui thread (which required if accessing ui elements).