定位小部件导致子部件消失/异常

Question

我目前正在学习 Flutter，并尝试使用 Stack 中的 Positioned 小部件将轮播定位在屏幕底部。目前，堆栈是一张地图，轮播位于其顶部。当我使用定位的小部件将轮播移动到底部时，它消失了，我遇到了这个错误。

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I/flutter (19228): Another exception was thrown: \'package:flutter/src/rendering/object.dart\': Failed assertion: line 1578 pos 12: \'!_debugDoingThisLayout\': is not true.\n    I/flutter (19228): Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#51ed3 relayoutBoundary=up4 NEEDS-LAYOUT NEEDS-PAINT\n    Restarted application in 1,970ms.\n    I/flutter (19228): \xe2\x95\x90\xe2\x95\x90\xe2\x95\xa1 EXCEPTION CAUGHT BY RENDERING LIBRARY \xe2\x95\x9e\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\n    I/flutter (19228): The following assertion was thrown during performResize():\n    I/flutter (19228): Horizontal viewport was given unbounded width.\n    I/flutter (19228): Viewports expand in the scrolling direction to fill their container.In this case, a horizontal\n    I/flutter (19228): viewport was given an unlimited amount of horizontal space in which to expand. This situation\n    I/flutter (19228): typically happens when a scrollable widget is nested inside another scrollable widget.\n    I/flutter (19228): If this widget is always nested in a scrollable widget there is no need to use a viewport because\n    I/flutter (19228): there will always be enough horizontal space for the children. In this case, consider using a Row\n    I/flutter (19228): instead. Otherwise, consider using the "shrinkWrap" property (or a ShrinkWrappingViewport) to size\n    I/flutter (19228): the width of the viewport to the sum of the widths of its children.\n    I/flutter (19228): \n    I/flutter (19228): When the exception was thrown, this was the stack:\n    I/flutter (19228): #0      RenderViewport.performResize.<anonymous closure> (package:flutter/src/rendering/viewport.dart:1155:15)\n    I/flutter (19228): #1      RenderViewport.performResize (package:flutter/src/rendering/viewport.dart:1182:6)\n    I/flutter (19228): #2      RenderObject.layout (package:flutter/src/rendering/object.dart:1619:9)\n    I/flutter (19228): #3      _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #4      RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #5      _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #6      RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #7      _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #8      RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #9      _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #10     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #11     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #12     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #13     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #14     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #15     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #16     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #17     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #18     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #19     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #20     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #21     RenderConstrainedBox.performLayout (package:flutter/src/rendering/proxy_box.dart:258:13)\n    I/flutter (19228): #22     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #23     RenderStack.performLayout (package:flutter/src/rendering/stack.dart:549:15)\n    I/flutter (19228): #24     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #25     MultiChildLayoutDelegate.layoutChild (package:flutter/src/rendering/custom_layout.dart:142:11)\n    I/flutter (19228): #26     _ScaffoldLayout.performLayout (package:flutter/src/material/scaffold.dart:339:7)\n    I/flutter (19228): #27     MultiChildLayoutDelegate._callPerformLayout (package:flutter/src/rendering/custom_layout.dart:212:7)\n    I/flutter (19228): #28     RenderCustomMultiChildLayoutBox.performLayout (package:flutter/src/rendering/custom_layout.dart:356:14)\n    I/flutter (19228): #29     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #30     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #31     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #32     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #33     _RenderCustomClip.performLayout (package:flutter/src/rendering/proxy_box.dart:1188:11)\n    I/flutter (19228): #34     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #35     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #36     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #37     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #38     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #39     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #40     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #41     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #42     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #43     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #44     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #45     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #46     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #47     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #48     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #49     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #50     RenderOffstage.performLayout (package:flutter/src/rendering/proxy_box.dart:2881:13)\n    I/flutter (19228): #51     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #52     RenderStack.performLayout (package:flutter/src/rendering/stack.dart:510:15)\n    I/flutter (19228): #53     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #54     __RenderTheatre&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #55     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #56     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #57     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #58     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #59     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #60     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #61     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #62     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #63     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #64     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #65     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #66     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #67     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #68     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #69     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #70     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #71     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #72     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #73     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #74     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #75     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #76     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #77     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #78     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #79     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #80     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #81     RenderOffstage.performLayout (package:flutter/src/rendering/proxy_box.dart:2881:13)\n    I/flutter (19228): #82     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #83     RenderStack.performLayout (package:flutter/src/rendering/stack.dart:510:15)\n    I/flutter (19228): #84     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #85     __RenderTheatre&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #86     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #87     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #88     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #89     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #90     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #91     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #92     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #93     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #94     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #95     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)\n    I/flutter (19228): #96     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)\n    I/flutter (19228): #97     RenderView.performLayout (package:flutter/src/rendering/view.dart:147:13)\n    I/flutter (19228): #98     RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:1509:7)\n    I/flutter (19228): #99     PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:768:18)\n    I/flutter (19228): #100    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:281:19)\n    I/flutter (19228): #101    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:677:13)\n    I/flutter (19228): #102    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:219:5)\n    I/flutter (19228): #103    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)\n    I/flutter (19228): #104    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)\n    I/flutter (19228): #105    _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:751:7)\n    I/flutter (19228): #107    _Timer._runTimers (dart:isolate/runtime/libtimer_impl.dart:382:19)\n    I/flutter (19228): #108    _Timer._handleMessage (dart:isolate/runtime/libtimer_impl.dart:416:5)\n    I/flutter (19228): #109    _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)\n    I/flutter (19228): (elided one frame from package dart:async)\n    I/flutter (19228): \n    I/flutter (19228): The following RenderObject was being processed when the exception was fired:\n    I/flutter (19228):   RenderViewport#90797 NEEDS-LAYOUT NEEDS-PAINT\n    I/flutter (19228):   creator: Viewport \xe2\x86\x90 _ScrollableScope \xe2\x86\x90 IgnorePointer-[GlobalKey#3c2b1] \xe2\x86\x90 Semantics \xe2\x86\x90 Listener \xe2\x86\x90\n    I/flutter (19228):   _GestureSemantics \xe2\x86\x90 RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#cd194] \xe2\x86\x90\n    I/flutter (19228):   _ScrollSemantics-[GlobalKey#45621] \xe2\x86\x90 RepaintBoundary \xe2\x86\x90 CustomPaint \xe2\x86\x90 RepaintBoundary \xe2\x86\x90\n    I/flutter (19228):   NotificationListener<ScrollNotification> \xe2\x86\x90 \xe2\x8b\xaf\n    I/flutter (19228):   parentData: <none> (can use size)\n    I/flutter (19228):   constraints: BoxConstraints(0.0<=w<=Infinity, h=180.0)\n    I/flutter (19228):   size: MISSING\n    I/flutter (19228):   axisDirection: right\n    I/flutter (19228):   crossAxisDirection: down\n    I/flutter (19228):   offset: _PagePosition#6c97d(offset: null, range: null..null, viewport: null, ScrollableState,\n    I/flutter (19228):   PageScrollPhysics -> ClampingScrollPhysics, IdleScrollActivity#73c09, ScrollDirection.idle)\n    I/flutter (19228):   anchor: 0.0\n    I/flutter (19228): This RenderObject had the following child:\n    I/flutter (19228):   RenderSliverFillViewport#ce224 NEEDS-LAYOUT NEEDS-PAINT\n    I/flutter (19228): \xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe2\x95\x90\xe

    

Answer 1

正如您的日志所解释的：

“约束：BoxConstraints(0.0<=w<=无穷大，h=180.0)”

您必须定义 的宽度，它Container是您的父级Swiper。您还必须使用行和列来组织堆栈中未定位的项目，以保持其布局在不同屏幕上保持一致。

添加这一行在你的Container：

 width: MediaQuery.of(context).size.width,

这将使您Swiper填满屏幕width，您可以将其修改为任何其他值以适合您的设计。