scrollByPageView method

void scrollByPageView(Size tabCenterSize, List<Size>? sizeList, ScrollController? scrollController, PageController pageController,)

根据pageController来设置偏移量

Implementation

void scrollByPageView(Size tabCenterSize, List<Size>? sizeList,
    ScrollController? scrollController, PageController pageController) {
  if (scrollController == null) return;
  var index = pageController.page!.ceil();
  var preIndex = pageController.page!.floor();
  var offsetPercent = pageController.page! % 1;
  var currentIndexHalfSize = sizeList![index] / 2;
  var preIndexHalfSize = sizeList[preIndex] / 2;

  var totalSize = Size(currentIndexHalfSize.width + preIndexHalfSize.width,
      currentIndexHalfSize.height + preIndexHalfSize.height);

  var startOffset = getTargetItemScrollStartOffset(sizeList, preIndex);
  var endSize = sizeList[preIndex] / 2 + startOffset;

  var contentInsertSize = getTabBarSize(sizeList);

  bool isVisible =
      isItemVisible(scrollController, index, sizeList, tabCenterSize * 2);

  var offset = 0.0;
  if (direction == Axis.horizontal) {
    if (isVisible) {
      if (endSize.width + totalSize.width > tabCenterSize.width) {
        if (endSize.width > tabCenterSize.width) {
          offset = endSize.width -
              tabCenterSize.width +
              offsetPercent * totalSize.width;
        } else {
          offset = offsetPercent *
              (totalSize.width + endSize.width - tabCenterSize.width);
        }
        if (contentInsertSize.width - offset - tabCenterSize.width >
            tabCenterSize.width) {
          scrollController.jumpTo(offset);
        }
      }
    } else {
      offset = startOffset.dx - tabCenterSize.width;
      scrollController.jumpTo(offset < 0 ? 0 : offset);
    }
  } else {
    //竖直方向
    if (isVisible) {
      if (endSize.height + totalSize.height > tabCenterSize.height) {
        if (endSize.height > tabCenterSize.height) {
          offset = endSize.height -
              tabCenterSize.height +
              offsetPercent * totalSize.height;
        } else {
          offset = offsetPercent *
              (totalSize.height + endSize.height - tabCenterSize.height);
        }

        if (contentInsertSize.height - offset - tabCenterSize.height >
            tabCenterSize.height) {
          scrollController.jumpTo(offset);
        }
      }
    } else {
      offset = startOffset.dy - tabCenterSize.height;
      scrollController.jumpTo(offset < 0 ? 0 : offset);
    }
  }
}