获取以下错误：
The method '[]' was called on null.
Receiver: null
Tried calling: []("uid")
The relevant error-causing widget was: Container file:///C:/Users/dkasa/Downloads/MICS%20Download/grocery_app/lib/screens/homeScreen.dart:28:14 When the exception was thrown, this was the stack:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
#1 _VendorCategoriesState.didChangeDependencies (package:grocery_app/widgets/categories_widget.dart:29:88)
#2 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4653:11)
#3 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4469:5)
下面的小部件categories_widget.dart在从vendor_home_screen调用时工作，但在从HomeScreen调用时出错。关于错误出现的原因，我看不出vendor_screen和HomeScreen之间有什么区别。
categories_widget
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:grocery_app/providers/store_provider.dart';
import 'package:grocery_app/services/product_services.dart';
import 'package:persistent_bottom_nav_bar/persistent-tab-view.dart';
import 'package:grocery_app/screens/product_list_screen.dart';
import 'package:provider/provider.dart';
class VendorCategories extends StatefulWidget {
@override
_VendorCategoriesState createState() => _VendorCategoriesState();
}
class _VendorCategoriesState extends State<VendorCategories> {
ProductServices _services = ProductServices();
List _catList = [];
@override
void didChangeDependencies() {
var _store = Provider.of<StoreProvider>(context);
FirebaseFirestore.instance
.collection('products').where('seller.sellerUid',isEqualTo: _store.storedetails['uid'])
.get()
.then((QuerySnapshot querySnapshot) => {
querySnapshot.docs.forEach((doc) {
//add all this in a list
setState(() {
_catList.add(doc['category']['mainCategory']);
});
}),
});
super.didChangeDependencies();
}
@override
Widget build(BuildContext context) {
var _storeProvider = Provider.of<StoreProvider>(context);
return FutureBuilder(
future: _services.category.get(),
builder: (BuildContext context,AsyncSnapshot<QuerySnapshot>snapshot){
if(snapshot.hasError){
return Center(child: Text('Something went wrong..'));
}
if(_catList.length==0){
return Center(child: CircularProgressIndicator(),);
}
if(!snapshot.hasData){
return Container();
}
return SingleChildScrollView(
child: Column(
children: [
Padding(
padding: const EdgeInsets.all(8.0),
child: Material(
elevation: 4,
borderRadius: BorderRadius.circular(6),
child: Container(
height: 60,
width: MediaQuery.of(context).size.width,
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(6),
image: DecorationImage(
fit: BoxFit.cover,
image: AssetImage('images/background.JPG')
)
),
child: Center(
child: Text('Shop by Category',style: TextStyle(
shadows: <Shadow>[
Shadow(
offset: Offset(2.0,2.0),
blurRadius: 3.0,
color: Colors.black
)
],
color: Colors.white,
fontWeight: FontWeight.bold,
fontSize: 30
),),
),
),
),
),
Wrap(
direction: Axis.horizontal,
children: snapshot.data.docs.map((DocumentSnapshot document){
return _catList.contains(document.data()['name']) ? //only if _catlList contain the category name from selected vendor
InkWell(
onTap: (){
_storeProvider.selectedCategory(document.data()['name']);
_storeProvider.selectedCategorySub(null);
pushNewScreenWithRouteSettings(
context,
settings: RouteSettings(name: ProductListScreen.id),
screen: ProductListScreen(),
withNavBar: true,
pageTransitionAnimation: PageTransitionAnimation.cupertino,
);
},
child: Container(
width: 120,height: 150,
child: Container(
decoration: BoxDecoration(
color: Colors.white,
border: Border.all(
color: Colors.grey,
width: .5
)
),
child: Column(
children: [
Center(
child: Image.network(document.data()['image']),
),
Padding(
padding: const EdgeInsets.only(left: 8,right: 8),
child: Text(document.data()['name'],textAlign: TextAlign.center,),
),
],
),
),
),
) : Text('');
}).toList(),
),
],
),
);
});
}
}
卖家主页屏幕
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:grocery_app/widgets/categories_widget.dart';
import 'package:grocery_app/widgets/vendor_appbar.dart';
import 'package:grocery_app/widgets/vendor_banner.dart';
import 'package:grocery_app/widgets/products/featured_products.dart';
import 'package:grocery_app/widgets/products/best_selling_product.dart';
import 'package:grocery_app/widgets/products/recently_added_products.dart';
class VendorHomeScreen extends StatelessWidget {
static const String id = 'vendor-screen';
@override
Widget build(BuildContext context) {
return Scaffold(
body: NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
return [
VendorAppBar(),
];
},
body: ListView(
physics: NeverScrollableScrollPhysics(),
shrinkWrap: true,
children: [
VendorBanner(),
VendorCategories(),
//Recently Added Products
//Best Selling Products
//Featured Products
RecentlyAddedProducts(),
FeaturedProducts(),
BestSellingProduct()
],
),
),
);
}
}
主屏幕
import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';
import 'package:grocery_app/providers/store_provider.dart';
import 'package:grocery_app/widgets/categories_widget.dart';
import 'package:grocery_app/widgets/image_slider.dart';
import 'package:grocery_app/widgets/my_appbar.dart';
import 'package:grocery_app/widgets/near_by_store.dart';
import 'package:grocery_app/widgets/top_pick_scree.dart';
import 'package:provider/provider.dart';
class HomeScreen extends StatelessWidget {
static const String id = 'home-screen';
@override
Widget build(BuildContext context) {
Provider.of<StoreProvider>(context,listen:false);
return Scaffold(
backgroundColor: Colors.grey[200],
body: NestedScrollView(
headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled){
return [
MyAppBar()
];
},
body: ListView(
shrinkWrap: true,
padding: EdgeInsets.only(top: 0.0),
children: [
ImageSlider(),
Container(
color: Colors.white,
child: VendorCategories(),
),
Container(
color: Colors.white,
child: TopPickStore(),
),
Padding(
padding: const EdgeInsets.only(top: 6),
child: NearByStores(),
),
],
),
),
);
}
}
由于Home已经有一个列表，所以当添加另一个列表时会出现问题：
body: ListView(
ShrinkWrap: true,
padding: EdgeInsets.only(top: 0.0),
children: [
ImageSlider(),
Container(
color: Colors.white,
child: VendorCategories(),
),
添加sinkWrap :true在你的主页上，然后再试一次，希望这能解决你的问题。