I am working on a project and stuck on this for 3 days now. The project reads a json, using an adapter, and fragments.
json: https://opendata.visitflanders.org/accessibility/activities/sport_v2.json
fragment_list_of_sports.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ListOfSportsFragment">
<!-- TODO: Update blank fragment layout -->
<TextView
android:id="@ id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="List of sports and locations"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.022" />
<androidx.recyclerview.widget.RecyclerView
android:id="@ id/rvSportList"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<Button
android:id="@ id/btnBack"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Back"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.049"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.976" />
</androidx.constraintlayout.widget.ConstraintLayout>
ListOfSportsFragment.kt:
package vives.be.bedoerikproject
import SportsAdapter
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.core.view.get
import androidx.fragment.app.Fragment
import androidx.recyclerview.widget.LinearLayoutManager
import kotlinx.android.synthetic.main.fragment_list_of_sports.*
import kotlinx.android.synthetic.main.fragment_list_of_sports.view.*
import org.json.JSONException
import org.json.JSONObject
class ListOfSportsFragment : Fragment() {
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
val view = inflater.inflate(R.layout.fragment_list_of_sports, container, false)
val sportList: ArrayList<SportModelClass> = ArrayList()
try {
// As we have JSON object, so we are getting the object
//Here we are calling a Method which is returning the JSON object
val obj = JSONObject("Sports.json")
// fetch JSONArray named users by using getJSONArray
val sportsArray = obj.getJSONArray("sports")
// Get the users data using for loop i.e. id, name, email and so on
for (i in 0 until sportsArray.length()) {
// Create a JSONObject for fetching single User's Data
val sport = sportsArray.getJSONObject(i)
// Fetch id store it in variable
val id = sport.getInt("business_product_id")
val name = sport.getString("name")
val city_name = sport.getString("city_name")
val postal_code = sport.getInt("postal_code")
val website = sport.getString("website")
val phone = sport.getString("phone1")
val email = sport.getString("email")
// Now add all the variables to the data model class and the data model class to the array list.
val sportDetails =
SportModelClass(id, name, postal_code, city_name, phone, email, website)
// add the details in the list
sportList.add(sportDetails)
}
} catch (e: JSONException) {
//exception
e.printStackTrace()
}
// Set the LayoutManager that this RecyclerView will use.
rvSportList.layoutManager = LinearLayoutManager(activity) //rv = reciycleview
// Adapter class is initialized and list is passed in the param.
val itemAdapter = SportsAdapter(requireContext(), sportList)
// adapter instance is set to the recyclerview to inflate the items.
rvSportList.adapter = itemAdapter
return view
}
}
SportsAdapter:
import vives.be.bedoerikproject.SportModelClass
import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import vives.be.bedoerikproject.R
import kotlinx.android.synthetic.main.sport_model_layout.view.*
class SportsAdapter(val context: Context, val items: ArrayList<SportModelClass>) :
RecyclerView.Adapter<SportsAdapter.ViewHolder>() {
/**
* Inflates the item views which is designed in xml layout file
*
* create a new
* {@link ViewHolder} and initializes some private fields to be used by RecyclerView.
*/
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
return ViewHolder(
LayoutInflater.from(context).inflate(
R.layout.sport_model_layout,
parent,
false
)
)
}
/**
* Binds each item in the ArrayList to a view
*
* Called when RecyclerView needs a new {@link ViewHolder} of the given type to represent
* an item.
*
* This new ViewHolder should be constructed with a new View that can represent the items
* of the given type. You can either create a new View manually or inflate it from an XML
* layout file.
*/
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val item = items.get(position)
holder.name.text = item.name
holder.city_name.text = item.city_name
holder.postal_code.text = item.postal_code.toString()
holder.website.text = item.website
holder.phone1.text = item.phone1
holder.email.text = item.email
}
/**
* Gets the number of items in the list
*/
override fun getItemCount(): Int {
return items.size
}
/**
* A ViewHolder describes an item view and metadata about its place within the RecyclerView.
*/
class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
// Holds the TextView that will add each item to
val name = view.name
val city_name = view.city_name
val postal_code = view.postal_code
val website = view.website
val phone1 = view.phone1
val email = view.email
}
}
SportModelClass.kt:
package vives.be.bedoerikproject
class SportModelClass (
val business_product_id : Int,
val name : String,
val postal_code : Int,
val city_name : String,
val phone1 : String,
val email : String,
val website : String
)
And I get an error in ListOfSportsFragment in line 60, this one:
E/AndroidRuntime: FATAL EXCEPTION: main Process: vives.be.bedoerikproject, PID: 7302 java.lang.NullPointerException: Attempt to invoke virtual method 'androidx.recyclerview.widget.RecyclerView$LayoutManager androidx.recyclerview.widget.RecyclerView.getLayoutManager()' on a null object reference at vives.be.bedoerikproject.ListOfSportsFragment.onCreateView(ListOfSportsFragment.kt:60) at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2995) at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:523) at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:261) at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1840) at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1764) at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1701) at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:488) at android.os.Handler.handleCallback(Handler.java:938) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:223) at android.app.ActivityThread.main(ActivityThread.java:7656) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) Disconnected from the target VM, address: 'localhost:52495', transport: 'socket'
CodePudding user response：
Use requireActivity() like this:
rvSportList.layoutManager = LinearLayoutManager(requireActivity())
CodePudding user response：
Could you try move your codes from onCreateView to onViewCreated fun on your fragment and use 'context' instead of 'requireContext()'. Hope it hepls.
CodePudding user response：
You can use synthetic view binding like this only after your fragment onCreateView() has returned.
Move the view setup code using synthetics such as rvSportList.layoutManager = LinearLayoutManager(activity) //rv = reciycleview to e.g. onViewCreated().
Also worth noting that the kotlin-android-extensions plugin that provides synthetic view binding is deprecated. Consider using view binding instead.
CodePudding user response：
This is your error:
java.lang.NullPointerException: Attempt to invoke virtual method
'androidx.recyclerview.widget.RecyclerView$LayoutManager
androidx.recyclerview.widget.RecyclerView.getLayoutManager()'
on a null object reference at
vives.be.bedoerikproject.ListOfSportsFragment.onCreateView(ListOfSportsFragment.kt:60)
It's trying to call a method (getLayoutManager()) on something that's supposed to be a RecyclerView, but it's not - it's null. Can't call a method on a null object, so you get the NullPointerException
This is line 60, where the log tells you the error is happening:
rvSportList.layoutManager = LinearLayoutManager(activity) //rv = reciycleview
So if the problem is calling methods on a null RecyclerView, and it's happening on that line, then rvSportList isn't a RecyclerView, it's null.
You're getting that magic rvSportList variable from the Kotlin synthetic extensions you're using, which have been deprecated for a long time. You should use View Binding instead - but in the meantime, try this - the basic way to find a view:
val rvSportList = view.findViewById<RecyclerView>(R.id.rvSportList)
rvSportList.layoutManager = LinearLayoutManager(requireContext())
// etc