在null上调用了方法'[]‘。Receiver:空，尝试调用：[]("pictures")

Question

你好吗？我需要我的代码.No的帮助，无论我如何寻找问题，我找不到原因。我使用futureBuilder从firebase收集数据，并将其显示在应用程序中。当我执行我说的代码时:方法'[]‘在null上被调用。接收者:空，已尝试调用：。

代码

Container(
                    child: FutureBuilder(
                      future: roomProduct.RoomData.doc().get(),
                      builder: (context, snap) {
                        if (snap.connectionState ==
                            ConnectionState.done) {
                          Map<String, dynamic> docs = snap.data.data();
                          return ListView(
                            shrinkWrap: true,
                            children: [
                              Padding(
                                padding: const EdgeInsets.all(6.0),
                                child: Container(
                                  decoration: BoxDecoration(
                                      color: Colors.white,
                                      borderRadius: BorderRadius.circular(10.0),
                                      boxShadow: [
                                        BoxShadow(
                                            color: Colors.grey,
                                            offset: Offset(-2,-1),
                                            blurRadius: 5
                                        )
                                      ]
                                  ),
                                  child: GestureDetector(

                                    child: Column(
                                      children: [
                                        Row(
                                          mainAxisAlignment: MainAxisAlignment.center,
                                          children: [
                                            ClipRRect(
                                                borderRadius: BorderRadius.circular(7.0),
                                                child: Image.network(

                                                  "${docs['pictures'][0]}",
                                                  height: 500,
                                                  width: 450,
                                                )
                                            ),
                                          ],
                                        ),
                                        Center(child: Text('${docs['name']} \n',style: 
                                       TextStyle(fontSize: 24.0,))),
                                        Center(child: Text('id:     ${docs['price']} \n',style: 
                                     TextStyle(fontSize: 24.0,))),
                                      ],
                                    ),
                                  ),
                                ),
                              )
                            ],
                          );
                        }
                        return Container();
                      },

                    ),
                  )

错误

The following NoSuchMethodError was thrown building FutureBuilder<DocumentSnapshot>(dirty, state: 
_FutureBuilderState<DocumentSnapshot>#59eb3):
 The method '[]' was called on null.
  Receiver: null
 Tried calling: []("pictures")

 The relevant error-causing widget was: 
   FutureBuilder<DocumentSnapshot> 
   
   When the exception was thrown, this was the stack: 
   #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
    #1      _IncorpoBidPageState.build.<anonymous closure>.<anonymous closure> 
   (package:MerchantIsland/bidPages/roomPage.dart:122:62)
   #2      _FutureBuilderState.build (package:flutter/src/widgets/async.dart:773:55)
   #3      StatefulElement.build (package:flutter/src/widgets/framework.dart:4612:27)
   #4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4495:15)
   ...
 ====================================================================================================
  /DynamiteModule( 4330): Local module descriptor class for providerinstaller not found.
  I/DynamiteModule( 4330): Considering local module providerinstaller:0 and remote module 
   providerinstaller:0
   W/ProviderInstaller( 4330): Failed to load providerinstaller module: No acceptable module found. 
  Local version is 0 and remote version is 0.
  W/DynamiteModule( 4330): Local module descriptor class for providerinstaller not found.
  I/DynamiteModule( 4330): Considering local module providerinstaller:0 and remote module 
  providerinstaller:0
  W/ProviderInstaller( 4330): Failed to load providerinstaller module: No acceptable module found. 
  Local version is 0 and remote version is 0.
  I/FirebaseAuth( 4330): [FirebaseAuth:] Preparing to create service connection to fallback 
   implementation
   W/System  ( 4330): Ignoring header X-Firebase-Locale because its value was null.

Answer 1

这是因为您正在尝试调用docs['pictures']，而您在这里发布的代码片段中没有声明docs。这就是为什么它会给出一个空值错误，因为该变量对于编译器来说是未知的，所以它将其视为空值。因此，您不能访问null变量的'pictures‘属性。

尝试预先声明docs变量，在使用它之前，只需执行null检查该值是否为null或其他值。