如何在flutter普通类中获取本地JSON

Question

服务-> math_logic.dart 它只是数学计算页面，所以我不用于 StateFul 小部件我得到的错误是 Futur 不是 String 的子类型 future is not a type Strint As cast...

import 'package:flutter/services.dart';

class Logic {
//Get JSON
  final response =
      rootBundle.loadString('assets/file/Data.json').then((value) => value);
  
//Vehicle Age Method
  vehicleAge(DateTime doPurchase, DateTime doRenewel) {
    var vAge = doPurchase.difference(doRenewel).abs().inDays.toInt();
    return vAge;
  }

 

// below Five Years Method

  belowFiveYear(int age, int fiveyear, int getInt, String zone,
      String odBasicRate, int basicTP) {
    response.then((value) => {print(value)});

    if (age <= fiveyear && getInt == 76150 && zone == 'Zone A') {
      odBasicRate = response[0]['Zone A']; //Error Here, don't get a json Data
      basicTP = 752;
      return [odBasicRate, basicTP];
    }
    
    
  }
}

下面给出我的 json Data Data.json

[
  
  {
    "Product no": 1,
    "Type of Vehicle": "Two Wheeler",
    "Vehicle Age": "Vehicle Age <= 5 years",
    "CC": "Upto 150 CC",
    "Zone A": "1.708",
    "Zone B": "1.676",
    "Zone C": "NA",
    "TP Premium": "-",
    "Per passenger": "-",
    "LT TP Premium": "-",
    "Option 1": "-",
    "Option 2": "-",
    "Discount": "-",
    "Rate percentage": "-"

  }etc..

[My code page is below][1]
  
]

Answer 1

loadString是一个异步方法，因此返回一个Future<String> 。 Future<T>.then()方法也返回一个 Future，所以你的response变量实际上是Future<String>类型

简而言之，您需要一个在某处定义为async的方法来await该方法完成。 此线程提供了一些有关初始化依赖于异步调用的实例成员的见解和示例。