question: public boolean step ( ) { long current = System . currentTimeMillis ( ) ; if ( mStart == 0 || ( current - mStart < 0 ) ) { mProgress = 0 ; } else if ( current - mStart > mDuration ) { if ( mLoop ) { mProgress = 0 ; start ( ) ; return true ; } mProgress = 1 ; return false ; } else { mProgress = ( current - mStart ) / ( double ) mDuration ; } return true ; }
target:  Step in the animation. Will compute the current progress as well.