出现类似“String不是index的int类型的子类型”的错误

`[
    {
      "id": "1",
      "name": "Deva",
      "age": "20",
      "address": {
        "streetname": "Park street",
        "area": "Jjnagar",
        "place": "Pollachi",
        "pincode": "642001"
    },
      "phonenumber": "8877665544"
    }
] `

**这是我的json数据

我需要在代码中解析**

`body: FutureBuilder(
            future:
                DefaultAssetBundle.of(context).loadString("assets/data.json"),
            builder: (context, snapshot) {
              var mydata = json.decode(snapshot.data.toString());
              return Center(
                child: Text(
                  mydata['name'],
                  style: const TextStyle(
                    color: Colors.deepPurple,
                    fontWeight: FontWeight.bold,
                    fontSize: 25,
                  ),
                ),
              );
            }));`

**这是密码

如何解决**