What do they utilize to build android apps with custom graphics and controls ?

Question

What I mean to say while you're just getting started with the development and say you add a slider theres a predefined skin for that and you can place it somewhere on the screen, but in some apps there are things like a knob in a place of slider which you can rotate to do the same stuff what the slider does . How do they do that, does it require openGL or something I am not asking for a complete tutorial or something just curious on what stuff goes into building such thing

Answer 1

Mostly, if something is not provided out of the box, you will have to build your own control.

For example, you mention a Knob. That isn't available in the Android SDK. Such a control could prove to be useful.

Here is a tutorial to build such a custom Control: http://go-lambda.blogspot.in/2012/02/rotary-knob-widget-on-android.html

This is an image of the final result from the tutorial linked above:

Here is an example of a custom slider / seek bar: http://permadi.com/blog/2011/11/android-sdk-custom-slider-bar-seekbar/

This should give you a rough idea on how to go about creating your own custom views.

And finally, what I personally find the best possible resource for keeping track of almost all good Custom Views is here: http://www.androidviews.net/

The androidviews.net website has shut down. Android Arsenal is a new website that lists several third party Android libraries.