AppMenuDragHelper.java 文件源码

AppMenuDragHelper(Activity activity, AppMenu appMenu, int itemRowHeight) {
    mActivity = activity;
    mAppMenu = appMenu;
    mItemRowHeight = itemRowHeight;
    Resources res = mActivity.getResources();
    mAutoScrollFullVelocity = res.getDimensionPixelSize(R.dimen.auto_scroll_full_velocity);
    // If user is dragging and the popup ListView is too big to display at once,
    // mDragScrolling animator scrolls mPopup.getListView() automatically depending on
    // the user's touch position.
    mDragScrolling.setTimeListener(new TimeAnimator.TimeListener() {
        @Override
        public void onTimeUpdate(TimeAnimator animation, long totalTime, long deltaTime) {
            ListPopupWindow popup = mAppMenu.getPopup();
            if (popup == null || popup.getListView() == null) return;

            // We keep both mDragScrollOffset and mDragScrollOffsetRounded because
            // the actual scrolling is by the rounded value but at the same time we also
            // want to keep the precise scroll value in float.
            mDragScrollOffset += (deltaTime * 0.001f) * mDragScrollingVelocity;
            int diff = Math.round(mDragScrollOffset - mDragScrollOffsetRounded);
            mDragScrollOffsetRounded += diff;
            popup.getListView().smoothScrollBy(diff, 0);

            // Force touch move event to highlight items correctly for the scrolled position.
            if (!Float.isNaN(mLastTouchX) && !Float.isNaN(mLastTouchY)) {
                menuItemAction(Math.round(mLastTouchX), Math.round(mLastTouchY),
                        ITEM_ACTION_HIGHLIGHT);
            }
        }
    });

    // We use medium timeout, the average of tap and long press timeouts. This is consistent
    // with ListPopupWindow#ForwardingListener implementation.
    mTapTimeout =
            (ViewConfiguration.getTapTimeout() + ViewConfiguration.getLongPressTimeout()) / 2;
    mScaledTouchSlop = ViewConfiguration.get(activity).getScaledTouchSlop();
}