How to implement Android listview opening gesture

Question

This is an open question about Android ListViews, Gestures and Animations. I'm really not familiar with the gestures in Android, so I'm just looking for ideas and grey matter on this.

Here's two screenshot and a video examples of the effect on what I'm trying to cogitate. Consider taking a look at the video, it's really worth it.

The screenshots are from an iOS open source project found here.

The question is, how would you implement a "listview opening" gesture like the one I see more and more often in iPhone/iPad apps, but for Android ?

Edit 1, idea 1:

Okay first idea, AFAIK the Pinch gesture is somehow like a dragging gesture, so I guess we can get the X and Y coordinates of the two fingers on the screen?

Next, the answer to this question may help, the basic idea is:

Get the index position of the first visible item in the list

Get the index position of the last visible item in the list

Iterate from the first index to the last with the getChildAt function

For each child, call the getLocationOnScreen method to get coordinates of the current iterated item

After that, some comparison between the pinch gesture coordinates and each item coordinates might be done inside the loop to get the two items between which the new row must me inserted.

Performances considerations appart I think it could work, but maybe there's a simpler way to get those two items(?).

Who's next? :)

Update:

Thanks for the tip @rhlnair, I take this occasion to tell everybody that I started to work on this on my spare time and you are more then welcome to help on this.

The project is at https://github.com/arnaudbos/Android-GestureListView. I started two different implementations on two different branches, and would enjoy anybody to create a new branch.

I have something really encouraging in branch "attemp-via-scale-gesture-detector" but some side effects from the ListView.

Come on folks!

Answer 1

seems to be a challenging idea..

i think some of the effect in clear app like dragging a selected row up/down can be taken from

https://github.com/commonsguy/cwac-touchlist

Answer 2

When doing a pinch gesture you have two fingers on the screen and therefore a point in the middle of those two points. That is simple euclidean arithmetic to find that middle point.

Then find as you say the element in the list that this point is above. You mention performance and I do not think this will be a problem. You are iteration a loop a few times and asking for coordinates. I have done much worse on touch events.

If the point between the pinch is above the middle of the list item you create the item above, and vice versa below.

See the section at the bottom where they use a scale listener: http://android-developers.blogspot.com/2010/06/making-sense-of-multitouch.html

Using the scale listener you can use the scale to find out if you create a new element. If the scale is above (you are "zooming" out) a threshold you create a new element and let the view repopulate from the list adapter.