scrolling - Drag n drop on touch devices

I notice that touch apps rarely make use of the "drag n drop" (dnd) idiom, and instead dragging is almost always used for scrolling.

Is there a reason for this? Is it confusing or "wrong" to use dnd on touch? What about where scrolling is also required: can they be mixed effectively?

Answer

I think there are several reasons for it.

1. First and foremost, it is tricky to do if you already have scrolling implemented. It is possible to do, but it would require solutions like lists where you can scroll in one direction (say, vertical), and then use the other direction to 'detach' the item from the list, after which you can drag it in any direction. That is not a trivial action to do, to learn, or (off topic here) to implement.


2. Lots of touch interfaces have been geared towards small screens. Drag & drop often doesn't make sense on those screens, as it usually works by showing two or more containers of items you can drag & drop items between. However, these small screens are usually designed in a way that there only is one such container visible at any time. Still, on tablets or other larger-screen touch enabled systems, it could be used.