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我试图用可重复的图像制作一个水平滚动的 ListView,让它看起来像是一个永远滚动的长图像(就像在 2d 平台游戏中一样)。
但是,当我将图像添加到 ListView.build(...) 方法时,我无法让它们正确缩放。我希望图像为 .fitHeight
,在尝试了所有我能想到的小部件之后,我得到了两种结果之一。
完整代码如下:
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
home: Scaffold(
body: MyHomePage(),
),
);
}
}
class MyHomePage extends StatefulWidget {
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
@override
Widget build(BuildContext context) {
/// Freezes app and prevents it from hot reload/rebuild until app is manually terminated.
Widget image = Image.asset('assets/repeatable-forest.jpg', fit: BoxFit.fitHeight);
/// Wrapping Image in a FittedBox works, but with a lot of exceptions/warnings
Widget fittedWrappedImage =
FittedBox(child: Image.asset('assets/repeatable-forest.jpg'), fit: BoxFit.fitHeight);
return ListView.builder(
scrollDirection: Axis.horizontal,
controller: ScrollController(),
itemBuilder: (BuildContext context, int index) {
return image; //fittedWrappedImage; <-- choose which one to test.
},
);
}
}
如果您想尝试使用示例图片(实际上看起来不错),您可以在此处下载“完整”存储库: https://github.com/joelbrostrom/infinite_listview_image_freeze_example
正如您在代码注释中看到的那样,Image.asset()
卡住应用程序并将其包装在 FittedBox
中,使其可运行但有异常(exception)。
在我的主要项目中,第二种方法在调试配置中出现异常,但在发布时卡住。也许这是一个线索?
这是我在 FittedBox
中包装图像时遇到的异常:
I/flutter (27099): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter (27099): The following assertion was thrown during performLayout():
I/flutter (27099): 'package:flutter/src/rendering/box.dart': Failed assertion: line 307 pos 12: 'width > 0.0': is not
I/flutter (27099): true.
I/flutter (27099):
I/flutter (27099): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter (27099): more information in this error message to help you determine and fix the underlying cause.
I/flutter (27099): In either case, please report this assertion by filing a bug on GitHub:
I/flutter (27099): https://github.com/flutter/flutter/issues/new?template=BUG.md
I/flutter (27099):
I/flutter (27099): When the exception was thrown, this was the stack:
I/flutter (27099): #2 BoxConstraints.constrainSizeAndAttemptToPreserveAspectRatio (package:flutter/src/rendering/box.dart:307:12)
I/flutter (27099): #3 RenderFittedBox.performLayout (package:flutter/src/rendering/proxy_box.dart:2288:26)
I/flutter (27099): #4 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #5 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #6 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #7 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #8 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #9 RenderSliverList.performLayout (package:flutter/src/rendering/sliver_list.dart:164:27)
I/flutter (27099): #10 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #11 RenderSliverPadding.performLayout (package:flutter/src/rendering/sliver_padding.dart:182:11)
I/flutter (27099): #12 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #13 RenderViewportBase.layoutChildSequence (package:flutter/src/rendering/viewport.dart:407:13)
I/flutter (27099): #14 RenderViewport._attemptLayout (package:flutter/src/rendering/viewport.dart:1322:12)
I/flutter (27099): #15 RenderViewport.performLayout (package:flutter/src/rendering/viewport.dart:1240:20)
I/flutter (27099): #16 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #17 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #18 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #19 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #20 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #21 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #22 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #23 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #24 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #25 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #26 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #27 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #28 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #29 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #30 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #31 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #32 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #33 MultiChildLayoutDelegate.layoutChild (package:flutter/src/rendering/custom_layout.dart:142:11)
I/flutter (27099): #34 _ScaffoldLayout.performLayout (package:flutter/src/material/scaffold.dart:350:7)
I/flutter (27099): #35 MultiChildLayoutDelegate._callPerformLayout (package:flutter/src/rendering/custom_layout.dart:212:7)
I/flutter (27099): #36 RenderCustomMultiChildLayoutBox.performLayout (package:flutter/src/rendering/custom_layout.dart:356:14)
I/flutter (27099): #37 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #38 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #39 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #40 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #41 _RenderCustomClip.performLayout (package:flutter/src/rendering/proxy_box.dart:1206:11)
I/flutter (27099): #42 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #43 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #44 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #45 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #46 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #47 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #48 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #49 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #50 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #51 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #52 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #53 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #54 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #55 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #56 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #57 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #58 RenderOffstage.performLayout (package:flutter/src/rendering/proxy_box.dart:3032:13)
I/flutter (27099): #59 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #60 RenderStack.performLayout (package:flutter/src/rendering/stack.dart:510:15)
I/flutter (27099): #61 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #62 __RenderTheatre&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #63 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #64 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #65 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #66 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #67 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #68 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #69 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #70 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #71 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #72 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13)
I/flutter (27099): #73 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7)
I/flutter (27099): #74 RenderView.performLayout (package:flutter/src/rendering/view.dart:151:13)
I/flutter (27099): #75 RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:1507:7)
I/flutter (27099): #76 PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:766:18)
I/flutter (27099): #77 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:329:19)
I/flutter (27099): #78 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:701:13)
I/flutter (27099): #79 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:268:5)
I/flutter (27099): #80 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:988:15)
I/flutter (27099): #81 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:928:9)
I/flutter (27099): #82 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:749:7)
I/flutter (27099): #91 _Timer._runTimers (dart:isolate/runtime/libtimer_impl.dart:382:19)
I/flutter (27099): #92 _Timer._handleMessage (dart:isolate/runtime/libtimer_impl.dart:416:5)
I/flutter (27099): #93 _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)
I/flutter (27099): (elided 10 frames from class _AssertionError and package dart:async)
I/flutter (27099):
I/flutter (27099): The following RenderObject was being processed when the exception was fired:
I/flutter (27099): RenderFittedBox#fc66f relayoutBoundary=up5 NEEDS-LAYOUT NEEDS-PAINT
I/flutter (27099): creator: FittedBox ← RepaintBoundary-[<0>] ← IndexedSemantics ←
I/flutter (27099): NotificationListener<KeepAliveNotification> ← KeepAlive ← AutomaticKeepAlive ← SliverList ←
I/flutter (27099): MediaQuery ← SliverPadding ← Viewport ← IgnorePointer-[GlobalKey#aa491] ← Semantics ← ⋯
I/flutter (27099): parentData: <none> (can use size)
I/flutter (27099): constraints: BoxConstraints(0.0<=w<=Infinity, h=1089.8)
I/flutter (27099): size: MISSING
I/flutter (27099): fit: fitHeight
I/flutter (27099): alignment: center
I/flutter (27099): textDirection: ltr
I/flutter (27099): This RenderObject had the following descendants (showing up to depth 5):
I/flutter (27099): RenderSemanticsAnnotations#bfe63 relayoutBoundary=up6 NEEDS-PAINT
I/flutter (27099): RenderImage#90dc8 relayoutBoundary=up7 NEEDS-PAINT
I/flutter (27099): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter (27099): Another exception was thrown: RenderBox was not laid out: RenderFittedBox#fc66f relayoutBoundary=up5 NEEDS-PAINT
I/flutter (27099): Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#4ba38 relayoutBoundary=up4 NEEDS-PAINT
I/flutter (27099): Another exception was thrown: 'package:flutter/src/rendering/sliver_multi_box_adaptor.dart': Failed assertion: line 467 pos 12: 'child.hasSize': is not true.
I/flutter (27099): Another exception was thrown: NoSuchMethodError: The getter 'scrollOffsetCorrection' was called on null.
I/flutter (27099): Another exception was thrown: NoSuchMethodError: The method 'debugAssertIsValid' was called on null.
I/flutter (27099): Another exception was thrown: NoSuchMethodError: The getter 'visible' was called on null.
I/flutter (27099): Another exception was thrown: NoSuchMethodError: The getter 'visible' was called on null.
D/libGLESv2(27099): STS_GLApi : DTS, ODTC are not allowed for Package : com.example.listview_image_scaling_issue
如有任何见解,我们将不胜感激!
最佳答案
嗯...文档说:
/// 2. The [ListView.builder] constructor takes an [IndexedWidgetBuilder], which
/// builds the children on demand. This constructor is appropriate for list views
/// with a large (or infinite) number of children because the builder is called
/// only for those children that are actually visible.
从理论上讲,这应该使您想做的事情成为可能。无论出于何种原因,您似乎都陷入了循环。 itemBuilder
不断被调用。我的猜测是,在 Assets 加载并实际呈现之前,无法确定它的尺寸。
您可以通过设置 itemCount: 1
来验证这一点,然后看到卡住消失了。此外,对 Image
的宽度设置初始约束有助于:
return ListView.builder(
scrollDirection: Axis.horizontal,
itemBuilder: (ctx, index) {
return ConstrainedBox(
constraints: BoxConstraints(
minWidth: MediaQuery.of(context).size.width,
maxWidth: double.infinity,
),
child: Image.asset(
'assets/repeatable-forest.jpg',
fit: BoxFit.fitHeight,
),
);
},
);
如果有人能深入了解为什么 itemBuilder
一直被调用,那就太棒了。
关于listview - 图像的无限 ListView 卡住应用程序或在布局期间抛出异常 [包括小应用程序],我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/56129410/
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