我使用Future构建器从json文件中获取数据，但是在运行应用程序时出现错误消息，列表正常运行，但该消息仍然出现。我希望知道问题的解决方案 我在另一个文件中使用了将来的构建器，但是错误涉及到此类
错误消息是=>调用getter'length'为null。
错误消息=>
I/flutter (24488): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (24488): The following NoSuchMethodError was thrown building FutureBuilder<String>(dirty, state:
I/flutter (24488): _FutureBuilderState<String>#10ff6):
I/flutter (24488): The getter 'length' was called on null.
I/flutter (24488): Receiver: null
I/flutter (24488): Tried calling: length
I/flutter (24488): Widget creation tracking is currently disabled. Enabling it enables improved error messages. It can
I/flutter (24488): be enabled by passing `--track-widget-creation` to `flutter run` or `flutter test`.
I/flutter (24488): When the exception was thrown, this was the stack:
I/flutter (24488): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
I/flutter (24488): #1 _parseJson (dart:convert-patch/convert_patch.dart:28:28)
I/flutter (24488): #2 JsonDecoder.convert (dart:convert/json.dart:493:36)
I/flutter (24488): #3 JsonCodec.decode (dart:convert/json.dart:151:41)
I/flutter (24488): #4 CateogryState.build.<anonymous closure> (package:e_menu/content/cateogry_list.dart:23:33)
I/flutter (24488): #5 _FutureBuilderState.build (package:flutter/src/widgets/async.dart)
I/flutter (24488): #6 StatefulElement.build (package:flutter/src/widgets/framework.dart:4047:27)
I/flutter (24488): #7 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3941:15)
I/flutter (24488): #8 Element.rebuild (package:flutter/src/widgets/framework.dart:3738:5)
I/flutter (24488): #9 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3924:5)
I/flutter (24488): #10 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4088:11)
I/flutter (24488): #11 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3919:5)
代码=>
child: FutureBuilder(
future: recipeList.getMethod(),
builder: (BuildContext context, AsyncSnapshot snapshot) {
List snap = snapshot.data;
List temp = [];
if (snapshot.connectionState == ConnectionState.waiting) {
return Center(
child: CircularProgressIndicator(),
);
}
if (snapshot.hasError) {
return Center(
child: new Text('Error ${snapshot.error}'),
);
}
if (widget.currentcatelog == 'All') {
temp = snap;
} else {
snap.asMap().forEach((index, value) {
if (snap[index]['catelog'] == widget.currentcatelog) {
temp.add(value);
}
});
}
return Padding(
padding: const EdgeInsets.all(12.0),
child: (temp.length == 0)
? Center(child: Text('No file for it'))
: GridView.builder(
gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: MediaQuery.of(context).orientation ==
Orientation.portrait
? 2
: 3,
childAspectRatio: (1 / 1.2),
),
physics: BouncingScrollPhysics(),
itemCount: temp.length,
scrollDirection: Axis.vertical,
itemBuilder: (BuildContext context, int index) {
if (! counter.containsKey(index)) {
counter[index] = 0;
print( counter[index]);
}
return Padding(
padding: const EdgeInsets.all(12),
child: GestureDetector(
onTap: () {
showDialog(
context: context,
builder: (context) {
return Item(list: snap,
index: index);
});
},
child: Hero(
tag: '${snap[index]['catelog']}${widget.name}',
child: SizedBox(
width: 70,
child: Card(
color: Colors.transparent,
elevation: 10.0,
child: Row(
children: <Widget>[
Expanded(
child: ClipRRect(
borderRadius:
BorderRadius.circular(20.0),
child: Stack(
fit: StackFit.expand,
children: <Widget>[
Container(
width: double.infinity,
child: Image.asset(
snap[index]['pic'],
fit: BoxFit.cover,
),
),
Align(
alignment:
Alignment.bottomCenter,
child: Container(
padding: EdgeInsets.symmetric(vertical: 10,horizontal: 30),
color: Colors.black38,
width:
MediaQuery.of(context)
.size
.width,
height: MediaQuery.of(context)
.size
.width/8.5,
child: Column(
mainAxisAlignment:
MainAxisAlignment
.start,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
snap[index]
['name'],
style: TextStyle(
color: Colors
.white,
fontSize:
18)),
Text(
'${snap[index]['price']} BHD',
style: TextStyle(
color: Colors
.white,
fontSize:
18)),
],
),
))
],
),
),
),
],
),
),
),
),
),
);
},
),
);
})),```