Flutter开发遇NoSuchMethodError：null对象调用placeName getter如何修复？

报错为典型的空指针调用异常：构建SearchScreen组件时，代码直接访问了AppData状态中存储的下车地址对象的placeName属性，但此时该地址对象尚未初始化，值为null，触发调用失败。

• 检查SearchScreen的build方法中所有引用placeName的代码，添加空安全处理
  所有类似Provider.of<AppData>(context).dropOffLocationAddress.placeName的写法，替换为：

  Provider.of<AppData>(context).dropOffLocationAddress?.placeName ?? "请选择下车地址"
  

• 初始化AppData时给下车地址属性赋初始空对象，避免为null
  在AppData类中修改属性定义：

  // 原来如果是 Address? dropOffLocationAddress; 改成下面的写法
  Address dropOffLocationAddress = Address();
  

  同时给Address类的所有属性设置默认值：

  class Address {
    String placeName = "";
    String placeId = "";
    double latitude = 0.0;
    double longitude = 0.0;
  }
  

• 给主页面的跳转回调添加非空校验，避免未拿到地址就执行导航逻辑
  修改main.dart第206行附近的代码：

  GestureDetector(
    onTap: () async {
      var res = await Navigator.push(context, MaterialPageRoute(builder: (context)=>SearchScreen()));
      if(res == "obtainDirection"){
        final appData = Provider.of<AppData>(context, listen: false);
        // 校验地址信息完整再执行路径规划
        if(appData.dropOffLocationAddress.placeName.isNotEmpty) {
          await getPlaceDirection();
        }
      }
    },
  )
  

• 优化地址查询接口的字段判空逻辑，避免接口返回异常导致赋值失败
  修改searchScreen.dart中的getPlaceAddressDetails方法：

  void getPlaceAddressDetails(String placeId, context) async{
    showDialog(context: context,
        builder: (BuildContext context) => ProgressDialog(message: "Setting DropOff, Please wait ...",)
    );
    String placeDetailsUrl = "https://maps.googleapis.com/maps/api/place/details/json?place_id=$placeId&key=$mapKey";
    var res = await RequestAssistant.getRequest(Uri.parse(placeDetailsUrl));
    Navigator.pop(context);
    if(res == "failed"){
      return;
    }
    if(res["status"] == "OK") {
      final result = res["result"];
      final geometry = result?["geometry"];
      final location = geometry?["location"];
      // 校验必填字段非空再赋值
      if(result != null && location != null) {
        Address address = Address();
        address.placeName = result["name"] ?? "";
        address.placeId = placeId;
        address.latitude = location["lat"]?.toDouble() ?? 0.0;
        address.longitude = location["lng"]?.toDouble() ?? 0.0;
        Provider.of<AppData>(context, listen: false).updateDropOffLocationAddress(address);
        print("This is Drop Off Location ::");
        print(address.placeName);
        Navigator.pop(context, "obtainDirection");
      }
    }
  }
  

内容的提问来源于stack exchange，提问作者Julían Meneses