失败的断言：第 1696 行 pos 12：'center!.parent == this'：不是真的

Question

I don't know Why I can't run my app. The previous times I built successfully, I don't change anything but at this time I can't build an app. Please help my fix this problem.

======== Exception caught by scheduler library =====================================================
The following assertion was thrown during a scheduler callback:
'package:flutter/src/rendering/viewport.dart': Failed assertion: line 1696 pos 12: 'center!.parent == this': is not true.


Either the assertion indicates an error in the framework itself, or we should provide substantially more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
  https://github.com/flutter/flutter/issues/new?template=2_bug.md

When the exception was thrown, this was the stack: 
#2      RenderViewport.indexOfFirstChild (package:flutter/src/rendering/viewport.dart:1696:12)
#3      RenderViewportBase.debugDescribeChildren (package:flutter/src/rendering/viewport.dart:968:17)
#4      DiagnosticableTreeNode.getChildren (package:flutter/src/foundation/diagnostics.dart:2994:48)
#5      DiagnosticsNode.toJsonMap.<anonymous closure> (package:flutter/src/foundation/diagnostics.dart:1567:32)
#6      DiagnosticsNode.toJsonMap (package:flutter/src/foundation/diagnostics.dart:1608:6)
...
====================================================================================================
E/flutter ( 8936): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: 'package:flutter/src/rendering/box.dart': Failed assertion: line 1938 pos 13: 'debugDoingThisResize || debugDoingThisLayout || _computingThisDryLayout ||
E/flutter ( 8936):               (RenderObject.debugActiveLayout == parent && _size._canBeUsedByParent)': RenderBox.size accessed beyond the scope of resize, layout, or permitted parent access. RenderBox can always access its own size, otherwise, the only object that is allowed to read RenderBox.size is its parent, if they have said they will. It you hit this assert trying to access a child's size, pass "parentUsesSize: true" to that child's layout().
E/flutter ( 8936): #0      _AssertionError._doThrowNew (dart:core-patch/errors_patch.dart:46:39)
E/flutter ( 8936): #1      _AssertionError._throwNew (dart:core-patch/errors_patch.dart:36:5)
E/flutter ( 8936): #2      RenderBox.size.<anonymous closure> (package:flutter/src/rendering/box.dart:1938:13)
E/flutter ( 8936): #3      RenderBox.size (package:flutter/src/rendering/box.dart:1951:6)
E/flutter ( 8936): #4      RenderProxyBoxWithHitTestBehavior.hitTest (package:flutter/src/rendering/proxy_box.dart:177:9)
E/flutter ( 8936): #5      RenderView.hitTest (package:flutter/src/rendering/view.dart:173:14)
E/flutter ( 8936): #6      RenderView.hitTestMouseTrackers (package:flutter/src/rendering/view.dart:190:5)
E/flutter ( 8936): #7      RendererBinding.dispatchEvent.<anonymous closure> (package:flutter/src/rendering/binding.dart:285:79)
E/flutter ( 8936): #8      MouseTracker.updateWithEvent (package:flutter/src/rendering/mouse_tracker.dart:297:92)
E/flutter ( 8936): #9      RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:285:22)
E/flutter ( 8936): #10     GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:374:7)
E/flutter ( 8936): #11     GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:338:5)
E/flutter ( 8936): #12     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:296:7)
E/flutter ( 8936): #13     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:279:7)
E/flutter ( 8936): #14     _rootRunUnary (dart:async/zone.dart:1370:13)
E/flutter ( 8936): #15     _CustomZone.runUnary (dart:async/zone.dart:1265:19)
E/flutter ( 8936): #16     _CustomZone.runUnaryGuarded (dart:async/zone.dart:1170:7)
E/flutter ( 8936): #17     _invoke1 (dart:ui/hooks.dart:182:10)
E/flutter ( 8936): #18     PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:282:7)
E/flutter ( 8936): #19     _dispatchPointerDataPacket (dart:ui/hooks.dart:96:31)
E/flutter ( 8936): 
E/flutter ( 8936): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: 'package:flutter/src/rendering/box.dart': Failed assertion: line 1938 pos 13: 'debugDoingThisResize || debugDoingThisLayout || _computingThisDryLayout ||
E/flutter ( 8936):               (RenderObject.debugActiveLayout == parent && _size._canBeUsedByParent)': RenderBox.size accessed beyond the scope of resize, layout, or permitted parent access. RenderBox can always access its own size, otherwise, the only object that is allowed to read RenderBox.size is its parent, if they have said they will. It you hit this assert trying to access a child's size, pass "parentUsesSize: true" to that child's layout().
E/flutter ( 8936): #0      _AssertionError._doThrowNew (dart:core-patch/errors_patch.dart:46:39)
E/flutter ( 8936): #1      _AssertionError._throwNew (dart:core-patch/errors_patch.dart:36:5)
E/flutter ( 8936): #2      RenderBox.size.<anonymous closure> (package:flutter/src/rendering/box.dart:1938:13)
E/flutter ( 8936): #3      RenderBox.size (package:flutter/src/rendering/box.dart:1951:6)
E/flutter ( 8936): #4      RenderProxyBoxWithHitTestBehavior.hitTest (package:flutter/src/rendering/proxy_box.dart:177:9)
E/flutter ( 8936): #5      RenderView.hitTest (package:flutter/src/rendering/view.dart:173:14)
E/flutter ( 8936): #6      RendererBinding.hitTest (package:flutter/src/rendering/binding.dart:490:16)
E/flutter ( 8936): #7      GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:346:7)
E/flutter ( 8936): #8      GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:338:5)
E/flutter ( 8936): #9      GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:296:7)
E/flutter ( 8936): #10     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:279:7)
E/flutter ( 8936): #11     _rootRunUnary (dart:async/zone.dart:1370:13)
E/flutter ( 8936): #12     _CustomZone.runUnary (dart:async/zone.dart:1265:19)
E/flutter ( 8936): #13     _CustomZone.runUnaryGuarded (dart:async/zone.dart:1170:7)
E/flutter ( 8936): #14     _invoke1 (dart:ui/hooks.dart:182:10)
E/flutter ( 8936): #15     PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:282:7)
E/flutter ( 8936): #16     _dispatchPointerDataPacket (dart:ui/hooks.dart:96:31)
E/flutter ( 8936): 

===============================================================================

Answer 1

If you are using Slivers, A workaround to this is pretty simple. But this is an issue in Flutter. But we can get a temp fix like this

CustomScrollView(
          slivers: <Widget>[
            SliverToBoxAdapter(
              child: SizedBox(),
            ),
            _feedListDelegate,])