system.reactive - Observable collection OnNext not firing -

i have simple observable collection, , onnext not firing.

list<int> intlist = new list<int>(){1,2,3}; iobservable<int> observablelist = intlist.toobservable();  idisposable subscription = observablelist.subscribe(     x =>  console.writeline("received {0} source.", x),             ex => console.writeline( "onerror: " + ex.message ),             ( ) => console.writeline( "oncompleted" )             );  intlist.add(4); 

the output getting follows.

received 1 source.

received 2 source.

received 3 source.

oncompleted

i expecting "received 4 source." after add 4 list.

can please throw light on doing wrong. new rx

this depends on order of operations.

if structure code this:

list<int> intlist = new list<int>() { 1, 2, 3 };  iobservable<int> observablelist = intlist.toobservable();  intlist.add(4);  idisposable subscription =     observablelist         .subscribe(             x => console.writeline("received {0} source.", x),             ex => console.writeline("onerror: " + ex.message),             () => console.writeline("oncompleted")); 

...then works expect.

the issue .subscribe run on current thread .toobservable(). actual code run return (iobservable<tsource>) new toobservable<tsource>(source, schedulerdefaults.iteration);. schedulerdefaults.iteration current thread.

you can see this code:

list<int> intlist = new list<int>() { 1, 2, 3 };  iobservable<int> observablelist = intlist.toobservable();  console.writeline("before subscription");  idisposable subscription =     observablelist         .subscribe(             x => console.writeline("received {0} source.", x),             ex => console.writeline("onerror: " + ex.message),             () => console.writeline("oncompleted"));  console.writeline("after subscription, before add");  intlist.add(4);  console.writeline("after add"); 

when run get:

before subscription received 1 source. received 2 source. received 3 source. oncompleted after subscription, before add after add 

so .add hasn't happened until after subscription complete.

now, if try around changing code intlist.toobservable(scheduler.default) new problem. running above code this:

before subscription after subscription, before add after add received 1 source. onerror: collection modified; enumeration operation may not execute. 

now clearly, have concurrency issue. shouldn't try manipulate collections , iterate them @ same time.