Allow dropdown to be positioned up or down

[wesleycho]

So given the robust positioning present in some of the other components, we actually have a request at work for doing so, and automatically positioning the appropriate direction when too close to the bottom (position="auto" functionality).

This would be a useful feature for those using dropdowns as a fancier version of a select element.

I'll probably end up tackling this, but if anyone wants to attempt it, I welcome it.

[deeg]

I had to do something like this at work also. I will try to make a PR if I have some time.

Wanted to put some code which might be helpful when building this feature:

menuPosition = $uibPosition.positionElements(
    element,
    controller.dropdownMenu,
    "bottom",
    true
);

//Check to see if it would go off bottom of screen
if ((menuPosition.top + controller.dropdownMenu[0].offsetHeight) >= ($window.pageYOffset + $window.innerHeight)) {
    menuPosition = $uibPosition.positionElements(
        element,
        controller.dropdownMenu,
        "top",
        true
    );
}

One thing to think about when building is at smaller window sizes it might go off bottom of screen, so you would position on top, but then could have an issue where it is going off top of screen or hidden by something like a navbar with a higher z-index.

[wesleycho]

I think that's ok to a degree - simple checks would be enough IMO, and maybe just use the existing stuff built into the position service.

[deeg]

Sounds good, and yeah agreed using the existing stuff in the position service!

[wesleycho]

Also the position service has support for auto placement - it should work similarly to how the tooltip/popover placement works.