Flutter|Flutter 扩展NestedScrollView （三）下拉刷新的解决 Flutter扩展NestedScrollView（三）下

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