JSON中的动态未知字段

Posted 2023-03-16

【中文标题】JSON中的动态未知字段

【英文标题】：Dynamic unknow field in JSON

【发布时间】：2020-02-29 12:54:13

【问题描述】：

我正在尝试从以下 URL 构建正确的类：

https://api.nasa.gov/neo/rest/v1/feed?start_date=2020-01-01&end_date=2020-01-08&api_key=DEMO_KEY

此时，我的结构如下：

data class NearEarthObject (val asteroidObjects : Map<String, DateSelected>)

data class DateSelected (val date: ArrayList<Asteroid>) 

 data class Asteroid(
    val id: Long,
    val codename: String,
    val closeApproachDate: String,
    val absoluteMagnitude: Double,
    val estimatedDiameter: Double,
    val relativeVelocity: Double,
    val distanceFromEarth: Double,
    val isPotentiallyHazardous: Boolean
)

这是我的 Java 代码：

class MainActivity : AppCompatActivity() 

    val URLAPI = Constants.BASE_URL

    override fun onCreate(savedInstanceState: Bundle?) 
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        asteroidActivityRv.layoutManager = LinearLayoutManager(this)
        asteroidActivityRv.adapter = null

        val retrofitAsteroids = Retrofit.Builder()
            .baseUrl(URLAPI)
            .addConverterFactory(GsonConverterFactory.create())
            .build()

        val apiAsteroid = retrofitAsteroids.create(ApiAsteroids::class.java)
        val callAsteroid = apiAsteroid.getAsteroids()
        callAsteroid.enqueue(object : Callback<NearEarthObject> 
            override fun onFailure(call: Call<NearEarthObject>?, t: Throwable?) 
                Log.e("TAG fail", t.toString())
            

            override fun onResponse(
                call: Call<NearEarthObject>,
                response: Response<NearEarthObject>
            ) 
                for (res in response.body().asteroidObjects) 
                    // Log.e("TAG result", res.value.date)
                
            

        )
    

但我不断收到以下错误：

 java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Set java.util.Map.entrySet()' on a null object reference
        at com.example.nasanwsproject.MainActivity$onCreate$1.onResponse(MainActivity.kt:44)
        at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68)

有人知道我做错了什么吗？

非常感谢您的帮助！

【参考方案1】：

看起来 response.body().asteroidObjects==null

我认为这个问题是因为你无法收到使用地图的响应。 它需要一个明确的类（包括字段和值。）