robotoaster robotoaster - 1 year ago 67
Dart Question

NoSuchMethod on RefreshIndicator

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/] 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 Source

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.

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