question: private void reflectMemberVariablesInLeftButton ( ) { final boolean lastPageReached = ( viewPager . getCurrentItem ( ) + 1 ) == pages . size ( ) ; final boolean buttonShouldBeInvisible = ( lastPageReached && disableLeftButtonOnLastPage ) || leftButtonDisabled ; final boolean buttonIsCurrentlyInvisible = leftButton . getVisibility ( ) == View . INVISIBLE ; final boolean shouldUpdateButton = buttonShouldBeInvisible != buttonIsCurrentlyInvisible ; if ( shouldUpdateButton ) { final Animator buttonAnimator = buttonShouldBeInvisible ? buttonAnimatorFactory . newLeftButtonDisappearAnimator ( leftButton ) : buttonAnimatorFactory . newLeftButtonAppearAnimator ( leftButton ) ; if ( buttonShouldBeInvisible ) { disableButton ( buttonAnimator , leftButton ) ; } else { enableButton ( buttonAnimator , leftButton ) ; } } }
target:  Enables or disables the left button, so that it matches the current member variables.