draw a elastic line in uiviewcontroller from touchbegin to touch move

i am implementing an application where i need to draw a lin开发者_C百科e on UIViewController.

line should straight and behave elastically, likethis Image, you can take reference to my question from this app.

i have gone through lot of tutorial, where i found this and implement too, but out put is like : line is not straight and also not behaves elastically.

if anyone know how can i implement such line, please guide me.

thanks.