Flutter|Flutter 扩展NestedScrollView （三）下拉刷新的解决
解决点之前的2个问题。开心的上项目试了下。完美。
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但是在使用官方的下拉刷新 RefreshIndicator 发现没法使用。
默默打开了源码，我们再来看一看。。
首先，我调试到这个，发现notification.depth不为0，其实也好理解，因为NestedScrollView里面有很多能滚动的东西。默认的RefreshIndicator要求的是必须是第一层的它才其效果。
/// A [ScrollNotificationPredicate] that checks whether
/// `notification.depth == 0`, which means that the notification did not bubble
/// through any intervening scrolling widgets.
bool defaultScrollNotificationPredicate(ScrollNotification notification) {
return notification.depth == 0;
}
复制代码那么我改成,再试试呢？
bool defaultScrollNotificationPredicate(ScrollNotification notification) {
return true;
return notification.depth == 0;
}
复制代码在_handleScrollNotification方法中，我们可以看到会有很多ScrollNotification进来，不同的，当你滑动在一个不能滚动的list里面的时候，获取的viewportDimension是为0.。这会覆盖掉之前有viewportDimension的值。
所以我做了以下改动
double maxContainerExtent = 0.0;
bool _handleScrollNotification(ScrollNotification notification) {
if (!widget.notificationPredicate(notification)) return false;
maxContainerExtent = math.max(
notification.metrics.viewportDimension, this.maxContainerExtent);
if (notification is ScrollStartNotification &&
notification.metrics.extentBefore == 0.0 &&
_mode == null &&
_start(notification.metrics.axisDirection)) {
setState(() {
_mode = _RefreshIndicatorMode.drag;
});
return false;
}
bool indicatorAtTopNow;
switch (notification.metrics.axisDirection) {
case AxisDirection.down:
indicatorAtTopNow = true;
break;
case AxisDirection.up:
indicatorAtTopNow = false;
break;
case AxisDirection.left:
case AxisDirection.right:
indicatorAtTopNow = null;
break;
}
if (indicatorAtTopNow != _isIndicatorAtTop) {
if (_mode == _RefreshIndicatorMode.drag ||
_mode == _RefreshIndicatorMode.armed)
_dismiss(_RefreshIndicatorMode.canceled);
} else if (notification is ScrollUpdateNotification) {
if (_mode == _RefreshIndicatorMode.drag ||
_mode == _RefreshIndicatorMode.armed) {
if (notification.metrics.extentBefore > 0.0) {
_dismiss(_RefreshIndicatorMode.canceled);
} else {
_dragOffset -= notification.scrollDelta;
_checkDragOffset(maxContainerExtent);
}
}
if (_mode == _RefreshIndicatorMode.armed &&
notification.dragDetails == null) {
// On iOS start the refresh when the Scrollable bounces back from the
// overscroll (ScrollNotification indicating this don't have dragDetails
// because the scroll activity is not directly triggered by a drag).
_show();
}
} else if (notification is OverscrollNotification) {
if (_mode == _RefreshIndicatorMode.drag ||
_mode == _RefreshIndicatorMode.armed) {
_dragOffset -= notification.overscroll / 2.0;
_checkDragOffset(maxContainerExtent);
}
} else if (notification is ScrollEndNotification) {
switch (_mode) {
case _RefreshIndicatorMode.armed:
_show();
break;
case _RefreshIndicatorMode.drag:
_dismiss(_RefreshIndicatorMode.canceled);
break;
default:
// do nothing
break;
}
}
return false;
}
复制代码对于NestedScrollView 来说。我们只需要关注最大能滚动viewportDimension，用这个来驱动整个下拉刷新.
Sample Code 用法跟官方一致
return NestedScrollViewRefreshIndicator(
onRefresh: onRefresh,
child: extended.NestedScrollView(
复制代码最后放上 Github extended_nested_scroll_view，如果你有更好的方式解决这个问题或者有什么不明白的地方，都请告诉我，由衷感谢。
【Flutter|Flutter 扩展NestedScrollView （三）下拉刷新的解决】
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