当我尝试访问JSON数据元素时出现Flutter:TypeError [英] Flutter: TypeError when I try to access elements of JSON data

问题描述

我正在尝试在动态列表视图上显示JSON数据的各个元素.但是，我不断收到类型'int'不是类型'String'的子类型"错误，我也不知道为什么.

I am trying to display individual elements of a JSON data on a dynamic listview. However, I keep getting "type 'int' is not a subtype of type 'String'" error and I have no idea why.

如果我在buildFlightsColumn函数的Row下的小部件中仅包含left()函数，则该代码有效.但是，一旦我包含了middle()和right()函数，我就会得到错误.

The code works if I include just the left() function in the widget located under the Row in the buildFlightsColumn function. But once I include the middle() and right() functions, I get the error.

Widget buildListView() {
    print(data);
    return ListView.builder(
      itemCount: data == null ? 0 : data.length,
      itemBuilder:  (context, index) {
        return buildFlightsColumn(data[index]); 
      }
    );
  }


  Widget buildFlightsColumn(dynamic item) => Container( 
    height: 150.0, 
    decoration: BoxDecoration(
    ),
    child: new Row( 
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      children: <Widget>[ 
        left(item['PlaceId']),
        middle(item['IataCode']),
        right()
      ],
    ),
  );

  Container left(dynamic item) {
    return new Container (
      child: Text(   
        item,
        textAlign: TextAlign.left,
        style: TextStyle(
          fontSize: 25.0,
          color: Colors.red,
        )
      ),
    );
  }

  Container middle(dynamic item) {
    return new Container( 
      child: Text(   
        item,
        textAlign: TextAlign.left,
        style: TextStyle(
          fontSize: 25.0,
          color: Colors.red,
        )
      ),
    );
  }

  Container right() {
    return new Container(
      child: RaisedButton( 
        onPressed: () { 
        },
        child: Text('Book Flights'),
      )
    );
  }

传递到buildFlightsColumn函数的数据是API请求返回的JSON数据:

The data passed into the buildFlightsColumn function is JSON data returned by the API request:

[{PlaceId: 65368, IataCode: LAX, Name: Los Angeles International, Type: Station, SkyscannerCode: LAX, CityName: Los Angeles, CityId: LAXA, CountryName: United States}, {PlaceId: 81727, IataCode: SFO, Name: San Francisco International, Type: Station, SkyscannerCode: SFO, CityName: San Francisco, CityId: SFOA, CountryName: United States}]

推荐答案

我认为问题在于PlaceId的类型为int，但是您尝试将其用作字符串.

I think the problem is that PlaceId is of type int but you try to use it as a String.

像这样更改代码:

Container left(dynamic item) {
return new Container (
  child: Text(   
    item.toString(), //change the type here
    textAlign: TextAlign.left,
    style: TextStyle(
      fontSize: 25.0,
      color: Colors.red,
    )
  ),
);
}

或者像这样:

 Widget buildFlightsColumn(dynamic item) => Container( 
height: 150.0, 
decoration: BoxDecoration(
),
child: new Row( 
  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
  children: <Widget>[ 
    left(item['PlaceId'].toString()) // convert item['placeId'] to String
    middle(item['IataCode']),
    right()
  ],
),

);

这篇关于当我尝试访问JSON数据元素时出现Flutter:TypeError的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！