do while loop not working properly in Titanium

Question

I think this should be an easy one but I am at my wits end.

I have created an app that cycles images through the screen in Titanium based on a delay "setInterval".

It cycles the images indefinitely but I would like to add in a function where the user can exit out of the cycle either on a time delay (a set number of iterations through the loop) or just when they push a button ("stop").

This code works to call a function that pulls an image off of my mamp server and creates a new window in Titanium where it is displayed:

setInterval(function(){call();}, 3000);

But when I try to take it a step further it doesn't work.

var keepGoing;
do {
setInterval(function(){call();}, 3000);
}
while (keepGoing);

function stop(e){
return keepGoing = false;
}

The function "stop" is called from my xml like so:

<Button id="stop" onClick="stop">stop</Button>

I've even tried just the following to no avail:

do {
setInterval(function(){call();}, 3000);
}
while (0 > 1);

So that it will cycle once and then stop working.

Any thoughts would be greatly appreciated!

Answer 1

Once you have started setInterval it will go in an infinite loop. If you want to stop the setInterval just call the clearInterval .

var interval;

interval = setInterval(function(){call();}, 3000);

function stop(e){
    clearInterval(interval);
}

This has done the work in my case.

Answer 2

You need pattern like that:

function loop () {
    call();   
    if (keepGoing) {
        setTimeout(loop, 3000);
    }
}
loop();

BTW, why the following code won't work is a popular question on interviews (I was asked that several times).

var keepGoing;
do { setInterval(call, 3000); } while (keepGoing);

The trick is, function passed into setInterval here will be called sometimes after 3s, but only if main thread will be free. And it never will be free - it's doing infinite loop.