NoSuchMethod on RefreshIndicator

Question

I have a layout which is using RefreshIndicator. It's child is CustomScrollView. However when onRefresh handler is called it throws an exception

[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)

Interesting part is that onRefresh completes successfully.

Also when immediate child of RefreshIndicator was a Flex it wasn't complaining.

Answer 1

It's hard to debug your issue because you didn't provide your code, but from the stack trace I can see that in your handleRefresh method, on line 49 of state.dart, you are calling new Future.sync(null) , which is trying to invoke null as a function.

Try using new Future.value(null) instead when you need a completed Future with value null . But RefreshIndicator doesn't do much when the returned Future completes immediately. You might want to look at this example for inspiration on how to use RefreshIndicator .

It probably wasn't complaining when the child was a Flex because a Flex doesn't scroll.