imitate Tumblr's menu, dragging animations look like a snake.

unexpected episode

I found another repository some time ago which implemments the same dragging effects. Besides, its unfold later-menu effects is much more consistent with original Tumblr effects. You can jump to this repository - here.

something irrelated

Several days ago, I installed the tumblr app into my genymotion device, and I was totally shocked by its amazing snake-menu animation which is quite smooth and fluent. Since I cannot clearly describe its visual effects, you’d better install this app and try it yourself.

Ok, I am always the one who would like to imitate beautiful things. And I was terribly curious about how its animation is implemented.

implement principle

So, at the first sight, do you have any idea about how this animation appears?

As you know, there are 6 imageviews: P1, P2, P3, P4, P5, P6, and P6 is the top-most imageview which is enabled to be dragged. You can easily figure it out that: P1 follows P2, P2 follows P3, P3 follows P4, P4 follows P5, P5 follows P6.

First of all, I used ViewDragHelper to make P6 draggable.

Then, ViewDragHelper.CallBack can tell us some information about P6’s status, such as dragging, released, and P6’s position change and so on. To lighten the parent ViewGroup’s job, I create a ViewTrackController to process P6’s status.

Afterwards, ViewTrackController is responsible for dealing with all the linkage animations: every time P6’s position changes, causes P5’s target position changes. Every time P5’s position change causes P4’s target position changes. The rest imageviews can be done in the same manner.

To make the animation pleasing to the eyes, facebook’s rebound sdk encounters with ViewTrackController. While reviewing the source code, you will find that each imageview has a SpringListener and a fllower-SpringListener. Obviously, P6’s follower is P5, P5’s follower is P4, P4’s follower is P3, etc… P6’s position change will notify P5’s follower-SpringListener, P5’s position change will notify P4’s follower-SpringListener, etc… That’s to say, P6’s position change leads the rest imageviews animate automatically.

Finally, the animated snake-menu is implemented by this way.