Question

我有一个使用RefreshIndicator的布局。它的孩子是CustomScrollView。但是，当调用onRefresh处理程序时，它会抛出异常

[ERROR:../../lib/tonic/logging/dart_error.cc(16)] Unhandled exception:
E/flutter (21060): NoSuchMethodError: The method 'call' was called on null.
E/flutter (21060): Receiver: null
E/flutter (21060): Tried calling: call()

E/flutter (21060): #0      Object._noSuchMethod (dart:core-patch/object_patch.dart:43)
E/flutter (21060): #1      Object.noSuchMethod (dart:core-patch/object_patch.dart:47)
E/flutter (21060): #2      new Future.sync (dart:async/future.dart:222)
E/flutter (21060): #3      MyHomePageState.handleRefresh (file:///home/swav/Git/flutter/status-app/lib/state/state.dart:49)
E/flutter (21060): #4      RefreshIndicatorState._show.<anonymous closure> (package:flutter/src/material/refresh_indicator.dart:319)
E/flutter (21060): #5      _RootZone.runUnary (dart:async/zone.dart:1371)
E/flutter (21060): #6      _FutureListener.handleValue (dart:async/future_impl.dart:129)
E/flutter (21060): #7      _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:636)
E/flutter (21060): #8      _Future._propagateToListeners (dart:async/future_impl.dart:665)
E/flutter (21060): #9      _Future._completeWithValue (dart:async/future_impl.dart:478)
E/flutter (21060): #10     _Future._asyncComplete.<anonymous closure> (dart:async/future_impl.dart:510)
E/flutter (21060): #11     _microtaskLoop (dart:async/schedule_microtask.dart:41)
E/flutter (21060): #12     _startMicrotaskLoop (dart:async/schedule_microtask.dart:50)

有趣的是onRefresh成功完成。

此外，当RefreshIndicator的直接孩子是Flex时，它没有抱怨。

Answer 1

很难调试你的问题，因为你没有提供你的代码，但是从堆栈跟踪中我可以看到，在handleRefresh方法中，在state.dart的第49行，你正在调用{{1试图调用new Future.sync(null)作为函数。

当您需要值null的已完成new Future.value(null)时，请尝试使用Future。但是当返回的Future立即完成时，null并没有做太多。您可能需要查看此example，了解如何使用RefreshIndicator。

当孩子是RefreshIndicator时，可能没有抱怨，因为Flex不会滚动。

关于RefreshIndicator的NoSuchMethod

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