Question

我正在尝试设置var json，但最后得到空指针。任何想法如何解决这一问题？还是Android新手

class Requester(activity: Activity) {
    ...
    var json : Info?  = null
    ...

    fun getData (counter : Int) {
        println("frist attemp"+json)// here it is null as it should be
        var show = 5*counter
        var url = "https://reqres.in/api/users?page=1&per_page=$show"
        var request = Request.Builder().url(url).build()
        val client = OkHttpClient()

        client.newCall(request).enqueue(object: Callback {
            override fun onResponse(call: Call?, response: Response?) {
                val body = response?.body()?.string()
                val gson = GsonBuilder().create()
                json = gson.fromJson(body,Info::class.java)//it should be init here

                activity.runOnUiThread {
                    dataSize = json!!.total
                    val adapter = UsersAdapter(activity ,json!!,activity)
                    if(activity is MainActivity)
                    activity.recycler_View.adapter = adapter

                }
                isLoading=false
                toast.cancel()


            }
            override fun onFailure(call: Call?, e: IOException?) {
                activity.runOnUiThread {
                    val adapter = UsersAdapter(activity ,Info(0,0,0,0,
                            listOf(Data(0,"NO CONECTION","",""))),activity)
                    activity.recycler_View.adapter = adapter
                    Toast.makeText(activity,"Failed to connect", Toast.LENGTH_SHORT).show()
                    toast.cancel()
                }

                isLoading=false


            }

        })
        println("end "+json)// here i get NULL any ideas why ?
    }

}

课程信息：

class Info(val page: Int,
           val per_page: Int,
           val total: Int,
           val total_pages: Int,
           val data: List<Data>)

班级数据：

class Data(val id: Int,
           val first_name: String,
           val last_name: String,
           val avatar: String)

UserActivity类：

class UserActivity : AppCompatActivity(){
var id : Int =0
val requester : Requester = Requester(this)
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_user)
     id = intent.getIntExtra("id",0)
    display()

}

private fun display() {
    textView_ID_DEFINED.setText("$id")
    requester.getData(id/3+1)
    var info : Info? = requester.json
    println("requester="+requester)
    println("requester.info= "+requester.json)

    if (info !=null){
        for (i in 0..info.data.size){
            if (id == info.data[i].id){
                println("ahoj")
            }
        }
    }
}

}

Stacktrace：

I /时间轴：时间轴：Activity_launch_request ID：com.example.android.zadanie时间：197846234 I / System.out：requester=com.example.android.zadanie.Requester@127852b requester.info = null I /时间轴：时间轴：Activity_idle ID：android.os.BinderProxy@5994e58时间：197846419 I / System.out：com.example.android.zadanie.Info@e380f1b中部

Answer 1

当HTTP请求完成时，应该初始化json变量（即fun onResponse）的初始化位置。这意味着getData在回调被实际调用之前之前结束，这就是为什么您得到null的原因。

为什么您的回调被异步调用？好的，这就是enqueue的实现方式，它的主要优点是它在一个单独的线程中运行HTTP请求，因此您的UI不会冻结。但是，在使用异步回调时，您必须考虑到您的代码可以在任何时间执行，即使您的应用程序不再处于前台（设想在应用程序运行时用户接听电话的情况）

OkHttp client.newcall（request）.enqueue ...获取空指针

1 个答案: