我正在构建我的第一个Flutter应用程序，但遇到了我无法解决的问题。
该应用从Firebase实时数据库中检索数据，将所有条目添加到列表中，并在PageView的第一页中显示所有条目。
当我以调试模式启动应用程序时，出现以下错误：
I/flutter ( 7901): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter ( 7901): The following NoSuchMethodError was thrown during performLayout():
I/flutter ( 7901): The getter 'key' was called on null.
I/flutter ( 7901): Receiver: null
I/flutter ( 7901): Tried calling: key
I/flutter ( 7901): User-created ancestor of the error-causing widget was:
I/flutter ( 7901): PageView-[#62d48] file:///home/amedeo/AndroidStudioProjects/pastore_app/lib/main.dart:241:17
I/flutter ( 7901): When the exception was thrown, this was the stack:
I/flutter ( 7901): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
I/flutter ( 7901): #1 SliverChildListDelegate.build (package:flutter/src/widgets/sliver.dart:672:27)
I/flutter ( 7901): #2 SliverMultiBoxAdaptorElement._build.<anonymous closure> (package:flutter/src/widgets/sliver.dart:1153:67)
I/flutter ( 7901): #3 _HashMap.putIfAbsent (dart:collection-patch/collection_patch.dart:137:29)
I/flutter ( 7901): #4 SliverMultiBoxAdaptorElement._build (package:flutter/src/widgets/sliver.dart:1153:26)
I/flutter ( 7901): #5 SliverMultiBoxAdaptorElement.createChild.<anonymous closure> (package:flutter/src/widgets/sliver.dart:1166:55)
I/flutter ( 7901): #6 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2328:19)
I/flutter ( 7901): #7 SliverMultiBoxAdaptorElement.createChild (package:flutter/src/widgets/sliver.dart:1159:11)
I/flutter ( 7901): #8 RenderSliverMultiBoxAdaptor._createOrObtainChild.<anonymous closure> (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:354:23)
I/flutter ( 7901): #9 RenderObject.invokeLayoutCallback.<anonymous closure> (package:flutter/src/rendering/object.dart:1797:58)
I/flutter ( 7901): #10 PipelineOwner._enableMutationsToDirtySubtrees (package:flutter/src/rendering/object.dart:875:15)
I/flutter ( 7901): #11 RenderObject.invokeLayoutCallback (package:flutter/src/rendering/object.dart:1797:13)
I/flutter ( 7901): #12 RenderSliverMultiBoxAdaptor._createOrObtainChild (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:343:5)
I/flutter ( 7901): #13 RenderSliverMultiBoxAdaptor.addInitialChild (package:flutter/src/rendering/sliver_multi_box_adaptor.dart:427:5)
I/flutter ( 7901): #14 RenderSliverFixedExtentBoxAdaptor.performLayout (package:flutter/src/rendering/sliver_fixed_extent_list.dart:196:12)
I/flutter ( 7901): #15 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #16 RenderViewportBase.layoutChildSequence (package:flutter/src/rendering/viewport.dart:406:13)
I/flutter ( 7901): #17 RenderViewport._attemptLayout (package:flutter/src/rendering/viewport.dart:1352:12)
I/flutter ( 7901): #18 RenderViewport.performLayout (package:flutter/src/rendering/viewport.dart:1270:20)
I/flutter ( 7901): #19 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #20 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #21 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #22 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #23 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #24 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #25 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #26 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #27 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #28 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #29 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #30 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #31 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #32 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #33 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #34 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #35 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #36 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #37 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #38 MultiChildLayoutDelegate.layoutChild (package:flutter/src/rendering/custom_layout.dart:142:11)
I/flutter ( 7901): #39 _ScaffoldLayout.performLayout (package:flutter/src/material/scaffold.dart:444:7)
I/flutter ( 7901): #40 MultiChildLayoutDelegate._callPerformLayout (package:flutter/src/rendering/custom_layout.dart:212:7)
I/flutter ( 7901): #41 RenderCustomMultiChildLayoutBox.performLayout (package:flutter/src/rendering/custom_layout.dart:356:14)
I/flutter ( 7901): #42 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #43 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #44 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #45 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #46 _RenderCustomClip.performLayout (package:flutter/src/rendering/proxy_box.dart:1232:11)
I/flutter ( 7901): #47 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #48 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #49 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #50 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #51 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #52 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #53 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #54 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #55 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #56 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #57 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #58 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #59 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #60 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #61 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #62 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #63 RenderOffstage.performLayout (package:flutter/src/rendering/proxy_box.dart:3140:13)
I/flutter ( 7901): #64 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #65 RenderStack.performLayout (package:flutter/src/rendering/stack.dart:510:15)
I/flutter ( 7901): #66 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #67 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #68 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #69 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #70 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #71 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #72 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #73 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #74 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #75 RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter ( 7901): #76 RenderObject.layout (package:flutter/src/rendering/object.dart:1701:7)
I/flutter ( 7901): #77 RenderView.performLayout (package:flutter/src/rendering/view.dart:152:13)
I/flutter ( 7901): #78 RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:1578:7)
I/flutter ( 7901): #79 PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:844:18)
I/flutter ( 7901): #80 RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:341:19)
I/flutter ( 7901): #81 WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:761:13)
I/flutter ( 7901): #82 RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:280:5)
I/flutter ( 7901): #83 SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1033:15)
I/flutter ( 7901): #84 SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:975:9)
I/flutter ( 7901): #85 SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:784:7)
I/flutter ( 7901): #94 _Timer._runTimers (dart:isolate-patch/timer_impl.dart:382:19)
I/flutter ( 7901): #95 _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:416:5)
I/flutter ( 7901): #96 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:172:12)
I/flutter ( 7901): (elided 8 frames from package dart:async and package dart:async-patch)
I/flutter ( 7901): The following RenderObject was being processed when the exception was fired: RenderSliverFillViewport#d6420 relayoutBoundary=up1 NEEDS-LAYOUT NEEDS-PAINT:
I/flutter ( 7901): creator: SliverFillViewport ← Viewport ← IgnorePointer-[GlobalKey#cec9a] ← Semantics ←
I/flutter ( 7901): _PointerListener ← Listener ← _GestureSemantics ←
I/flutter ( 7901): RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#9d04a] ← _PointerListener ← Listener
I/flutter ( 7901): ← _ScrollableScope ← _ScrollSemantics-[GlobalKey#04774] ← ⋯
I/flutter ( 7901): parentData: paintOffset=Offset(0.0, 0.0) (can use size)
I/flutter ( 7901): constraints: SliverConstraints(AxisDirection.right, GrowthDirection.forward, ScrollDirection.idle,
I/flutter ( 7901): scrollOffset: 0.0, remainingPaintExtent: 600.9, crossAxisExtent: 802.7, crossAxisDirection:
I/flutter ( 7901): AxisDirection.down, viewportMainAxisExtent: 600.9, remainingCacheExtent: 600.9 cacheOrigin: 0.0 )
I/flutter ( 7901): geometry: null
I/flutter ( 7901): no children current live
I/flutter ( 7901): This RenderObject has no descendants.
I/flutter ( 7901): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter ( 7901): Another exception was thrown: NoSuchMethodError: The method 'debugAssertIsValid' was called on null.
I/flutter ( 7901): Another exception was thrown: NoSuchMethodError: The getter 'visible' was called on null.
我尝试将GlobalKey添加到PageView键值中，但是没有用。
也许问题出在_onEntryChanged函数中，但我对此进行了评论，问题仍然存在。 这里是代码片段：
_onEntryChanged(Event event) {
var oldEntry = carList.singleWhere((entry) {
return entry.key == event.snapshot.key;
});
setState(() {
carList[carList.indexOf(oldEntry)] = Car.fromSnapshot(event.snapshot);
});
}
这是github存储库中所有文件的链接。 GitHub Repository
非常感谢您能为我提供帮助。
答案 0 :(得分：0)
请提供您认为会引发此错误的代码段
答案 1 :(得分：0)
只需将窗口小部件转换为 StatefulWidget
答案 2 :(得分：0)
我猜您的代码没有在应有的位置返回任何Widget。检查您是否在要调用要在屏幕上渲染的内容的地方添加了“ return”。我在通过调用映射列表的每个对象时忘记做一次，但没有在调用前添加“ return”。在那里，我得到了类似的错误日志。