如何访问片段视图中的findViewById-Kotlin

Question

我试图显示来自服务器json文件的数据列表。

当我尝试按Id选择视图时，它会抛出错误。

import android.os.AsyncTask
import android.os.Bundle
import android.util.Log
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ListView
import android.widget.ProgressBar
import kotlinx.android.synthetic.*
import org.json.JSONObject
import java.net.URL
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"
/**
* A simple [Fragment] subclass.
* Use the [HomeFragment.newInstance] factory method to
* create an instance of this fragment.
*/
class HomeFragment : Fragment() {
// TODO: Rename and change types of parameters
private var param1: String? = null
private var param2: String? = null
var dataList = ArrayList<HashMap<String, String>>()
private var res: View? = null ;

override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
arguments?.let {
param1 = it.getString(ARG_PARAM1)
param2 = it.getString(ARG_PARAM2)
}
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
this.res  = inflater.inflate(R.layout.fragment_home, container, false);
return res;
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
fetchJsonData().execute()
}
companion object {
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment HomeFragment.
*/
// TODO: Rename and change types and number of parameters
@JvmStatic
fun newInstance(param1: String, param2: String) =
HomeFragment().apply {
arguments = Bundle().apply {
putString(ARG_PARAM1, param1)
putString(ARG_PARAM2, param2)
}
}
}
/**
* Asyntask for getting list view
* from and point
*/
inner class fetchJsonData() : AsyncTask<String, Void, String>() {
override fun onPreExecute() {
super.onPreExecute()
}
override fun doInBackground(vararg params: String?): String? {
return URL("https://www.androdocs.com/files/uploads/original/sample-json-data-1567767983.txt").readText(
Charsets.UTF_8
)
}
override fun onPostExecute(result: String?) {
super.onPostExecute(result)
super.res.findViewById<ProgressBar>(R.id.loader).visibility = View.GONE
val jsonObj = JSONObject(result)
val usersArr = jsonObj.getJSONArray("users")
for (i in 0 until usersArr.length()) {
val singleUser = usersArr.getJSONObject(i)
val map = HashMap<String, String>()
map["name"] = singleUser.getString("name")
map["age"] = singleUser.getString("age")
map["city"] = singleUser.getString("city")
map["image"] = singleUser.getString("image")
dataList.add(map)
}
findViewById<ListView>(R.id.listView).adapter =
CustomAdapter(this@HomeFragment, dataList)
}
}
}

以下是我的代码。

在AsynTask中获取Json之后，我需要停止加载程序并传递加载的数据。这就是它投球失误的地方。

Answer 1

您可以尝试这种方法。

lateinit var progressBar: ProgressBar // Global declare

然后

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
progressBar = view.findViewById(R.id.loader)
// You can declare your listview here
fetchJsonData().execute()    
}

然后

override fun onPostExecute(result: String?) {
super.onPostExecute(result)
progressBar.visibility = View.GONE