我用 Python 创建了一个游戏，我想在 Flutter 中重新创建。它有一个 4 x 3 的网格布局板，如下图所示:
我想我想使用 Material 和子 Ink.image 来显示棋盘。
我的代码:
/*- Main method --------------------------------------------------- */
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text("Cat Attack"),
),
body: new Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
new Expanded(
child: new GridView.builder(
padding: const EdgeInsets.all(10.0),
gridDelegate: new SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: 4, // 4 columns of board buttons
childAspectRatio: 1.0,
crossAxisSpacing: 9.0,
mainAxisSpacing: 9.0),
itemCount: buttonsList.length,
itemBuilder: (context, i) => new SizedBox(
width: 100.0,
height: 100.0,
child: new Material(
elevation: 4.0,
shape: CircleBorder(),
color: Colors.transparent,
child: new Ink.image(
image: AssetImage('assets/animals/cat_blue_128.png'),
fit: BoxFit.cover,
width: 64.0,
height: 64.0,
),
),
),
),
),
new RaisedButton(
child: new Text(
"Reset",
style: new TextStyle(color: Colors.white, fontSize: 20.0),
),
color: Colors.red,
padding: const EdgeInsets.all(20.0),
onPressed: resetGame,
)
],
));
}
但是我收到了很多错误信息:
Performing hot reload... Syncing files to device Android SDK built for x86... I/flutter ( 5390): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ I/flutter ( 5390): The following assertion was thrown building LayoutBuilder: I/flutter ( 5390): A build function returned null. I/flutter ( 5390): The offending widget is: LayoutBuilder I/flutter ( 5390): Build functions must never return null. To return an empty space that causes the building widget to I/flutter ( 5390): fill available room, return "new Container()". To return an empty space that takes as little room as I/flutter ( 5390): possible, return "new Container(width: 0.0, height: 0.0)". I/flutter ( 5390): I/flutter ( 5390): When the exception was thrown, this was the stack: I/flutter ( 5390): #0 debugWidgetBuilderValue.<anonymous closure> (package:flutter/src/widgets/debug.dart:270:7) I/flutter ( 5390): #1 debugWidgetBuilderValue (package:flutter/src/widgets/debug.dart:287:4) I/flutter ( 5390): #2 _LayoutBuilderElement._layout.<anonymous closure> (package:flutter/src/widgets/layout_builder.dart:112:11) I/flutter ( 5390): #3 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2257:19) I/flutter ( 5390): #4 _LayoutBuilderElement._layout (package:flutter/src/widgets/layout_builder.dart:107:11) I/flutter ( 5390): #5 RenderObject.invokeLayoutCallback.<anonymous closure> (package:flutter/src/rendering/object.dart:1728:58) I/flutter ( 5390):
#6 PipelineOwner._enableMutationsToDirtySubtrees (package:flutter/src/rendering/object.dart:797:15) I/flutter ( 5390):
#7 RenderObject.invokeLayoutCallback (package:flutter/src/rendering/object.dart:1728:13) I/flutter ( 5390):
#8 _RenderLayoutBuilder.performLayout (package:flutter/src/widgets/layout_builder.dart:205:5) I/flutter ( 5390): #9 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#10 RenderConstrainedBox.performLayout (package:flutter/src/rendering/proxy_box.dart:259:13) I/flutter ( 5390): #11 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#12 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #13 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#14 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #15 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#16 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #17 _RenderCustomClip.performLayout (package:flutter/src/rendering/proxy_box.dart:1206:11) I/flutter ( 5390): #18 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#19 RenderConstrainedBox.performLayout (package:flutter/src/rendering/proxy_box.dart:259:13) I/flutter ( 5390): #20 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#21 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #22 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#23 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #24 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#25 RenderSliverGrid.performLayout (package:flutter/src/rendering/sliver_grid.dart:571:18) I/flutter ( 5390): #26 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#27 RenderSliverPadding.performLayout (package:flutter/src/rendering/sliver_padding.dart:182:11) I/flutter ( 5390): #28 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#29 RenderViewportBase.layoutChildSequence (package:flutter/src/rendering/viewport.dart:407:13) I/flutter ( 5390): #30 RenderViewport._attemptLayout (package:flutter/src/rendering/viewport.dart:1322:12) I/flutter ( 5390): #31 RenderViewport.performLayout (package:flutter/src/rendering/viewport.dart:1240:20) I/flutter ( 5390): #32 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#33 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #34 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#35 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #36 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#37 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #38 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#39 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #40 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#41 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #42 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#43 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #44 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#45 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #46 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#47 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #48 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#49 RenderFlex.performLayout (package:flutter/src/rendering/flex.dart:798:17) I/flutter ( 5390):
#50 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#51 MultiChildLayoutDelegate.layoutChild (package:flutter/src/rendering/custom_layout.dart:142:11) I/flutter ( 5390): #52 _ScaffoldLayout.performLayout (package:flutter/src/material/scaffold.dart:431:7) I/flutter ( 5390):
#53 MultiChildLayoutDelegate._callPerformLayout (package:flutter/src/rendering/custom_layout.dart:212:7) I/flutter ( 5390): #54 RenderCustomMultiChildLayoutBox.performLayout (package:flutter/src/rendering/custom_layout.dart:356:14) I/flutter ( 5390): #55 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#56 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #57 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#58 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #59 _RenderCustomClip.performLayout (package:flutter/src/rendering/proxy_box.dart:1206:11) I/flutter ( 5390): #60 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#61 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #62 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#63 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #64 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#65 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #66 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#67 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #68 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#69 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #70 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#71 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #72 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#73 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #74 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#75 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #76 RenderOffstage.performLayout (package:flutter/src/rendering/proxy_box.dart:3032:13) I/flutter ( 5390): #77 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#78 RenderStack.performLayout (package:flutter/src/rendering/stack.dart:510:15) I/flutter ( 5390):
#79 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#80 __RenderTheatre&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #81 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#82 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #83 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#84 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #85 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#86 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #87 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#88 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #89 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#90 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:105:13) I/flutter ( 5390): #91 RenderObject.layout (package:flutter/src/rendering/object.dart:1632:7) I/flutter ( 5390):
#92 RenderView.performLayout (package:flutter/src/rendering/view.dart:151:13) I/flutter ( 5390):
#93 RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:1507:7) I/flutter ( 5390):
#94 PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:766:18) I/flutter ( 5390):
#95 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:336:19) I/flutter ( 5390):
#96 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:701:13) I/flutter ( 5390):
#97 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:275:5) I/flutter ( 5390):
#98 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15) I/flutter ( 5390):
#99 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9) I/flutter ( 5390):
#100 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:751:7) I/flutter ( 5390): #102 _Timer._runTimers (dart:isolate/runtime/lib/timer_impl.dart:382:19) I/flutter ( 5390):
#103 _Timer._handleMessage (dart:isolate/runtime/lib/timer_impl.dart:416:5) I/flutter ( 5390):
#104 _RawReceivePortImpl._handleMessage (dart:isolate/runtime/lib/isolate_patch.dart:171:12) I/flutter ( 5390): (elided one frame from package dart:async) I/flutter ( 5390): ════════════════════════════════════════════════════════════════════════════════════════════════════ I/flutter ( 5390): Another exception was thrown: A build function returned null. I/chatty ( 5390): uid=10089(one.askit.cat_attack) Thread-2 identical 4 lines I/flutter ( 5390): Another exception was thrown: A build function returned null. Reloaded 2 of 438 libraries in 1 627ms. I/flutter ( 5390): Another exception was thrown: A build function returned null. I/chatty ( 5390): uid=10089(one.askit.cat_attack) Thread-2 identical 3 lines I/flutter ( 5390): Another exception was thrown: A build function returned null. I/flutter ( 5390): Another exception was thrown: Unable to load asset: assets/animals/cat_blue_128.png
我有动物图片，所以我不确定为什么会出现错误。
最佳答案
您需要在 pubspec.yaml 文件中定义要使用的资源。
来自文档-
Flutter uses the pubspec.yaml file, located at the root of your project, to identify assets required by an app.
像这样添加-
flutter:
assets:
- animals/cat_blue_128.png
此外，您可以删除 new 关键字来创建实例，因为 Dart 2 不需要它。
关于Flutter 创建游戏板，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/55430758/
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