I am new to android development. I have only been doing it for about a month now so I apologize if this is a simple question. I am keep getting the following error when trying to run my app
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.swiperefreshlayout.widget.SwipeRefreshLayout.setOnRefreshListener(androidx.swiperefreshlayout.widget.SwipeRefreshLayout$OnRefreshListener)' on a null object reference
at edu.cogswell.tn.prism.MainActivity.onCreate(MainActivity.kt:54)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Here is my code
package (package name)
import android.app.AlertDialog
import android.os.Bundle
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.navigation.findNavController
import androidx.navigation.ui.AppBarConfiguration
import androidx.navigation.ui.setupActionBarWithNavController
import androidx.navigation.ui.setupWithNavController
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.swiperefreshlayout.widget.SwipeRefreshLayout
import com.google.android.material.bottomnavigation.BottomNavigationView
import com.google.gson.Gson
import edu.cogswell.tn.prism.`interface`.NewsService
import edu.cogswell.tn.prism.adapter.viewHolder.ListSourceAdapter
import edu.cogswell.tn.prism.common.Common
import edu.cogswell.tn.prism.modle.WebSite
import io.paperdb.Paper
import kotlinx.android.synthetic.main.fragment_central.*
import retrofit2.Call
import retrofit2.Response
import javax.security.auth.callback.Callback
class MainActivity : AppCompatActivity() {
lateinit var layoutManager: LinearLayoutManager
lateinit var myService: NewsService
lateinit var adapter: ListSourceAdapter
lateinit var dialog: AlertDialog
var mSwipeRefreshLayout: SwipeRefreshLayout? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottomNaigationView)
val navController = findNavController(R.id.fragment)
val appBarConfiguration = AppBarConfiguration(
setOf(
R.id.central,
R.id.leftWing,
R.id.rightWing
)
)
setupActionBarWithNavController(navController, appBarConfiguration)
bottomNavigationView.setupWithNavController(navController)
Paper.init(this)
myService = Common.newsService
swipe_to_refresh_centreal.setOnRefreshListener {
loadWebSiteSource(true)
}
recycler_view_source_news_central.setHasFixedSize(true)
layoutManager = LinearLayoutManager(this)
recycler_view_source_news_central.layoutManager = layoutManager
//dialog = SpotsDialog.Builder().setContext(this).build()
loadWebSiteSource(false)
}
private fun loadWebSiteSource(isRefresh: Boolean) {
if(!isRefresh){
val cache = Paper.book().read<String>("cache")
if(cache != null && !cache.isBlank() && cache != "null"){
val website = Gson().fromJson<WebSite>(cache, WebSite::class.java)
adapter = ListSourceAdapter(baseContext, website)
adapter.notifyDataSetChanged()
recycler_view_source_news_central.adapter = adapter
}
else{
dialog.show()
myService.sources.enqueue(object:retrofit2.Callback<WebSite>{
override fun onResponse(call: Call<WebSite>, response: Response<WebSite>) {
adapter = ListSourceAdapter(baseContext,response!!.body()!!)
adapter.notifyDataSetChanged()
recycler_view_source_news_central.adapter = adapter
Paper.book().write("cache", Gson().toJson(response!!.body()!!))
dialog.dismiss()
}
override fun onFailure(call: Call<WebSite>, t: Throwable) {
Toast.makeText(baseContext,"Failed",Toast.LENGTH_SHORT).show()
}
})
}
}
else{
swipe_to_refresh_centreal.isRefreshing = true
myService.sources.enqueue(object:retrofit2.Callback<WebSite>{
override fun onResponse(call: Call<WebSite>, response: Response<WebSite>) {
adapter = ListSourceAdapter(baseContext,response!!.body()!!)
adapter.notifyDataSetChanged()
recycler_view_source_news_central.adapter = adapter
Paper.book().write("cache", Gson().toJson(response!!.body()!!))
swipe_to_refresh_centreal.isRefreshing=false
}
override fun onFailure(call: Call<WebSite>, t: Throwable) {
Toast.makeText(baseContext,"Failed",Toast.LENGTH_SHORT).show()
}
})
}
}
}
Here is the xml code
<?xml version="1.0" encoding="utf-8"?>
<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
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:id="@+id/swipe_to_refresh_centreal"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".Central">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recycler_view_source_news_central"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="10dp" />
</RelativeLayout>
</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>
Not too sure why I keep getting this error. I am using this tutorial https://www.youtube.com/watch?v=mvVcqzJYAbY For reference.
Thank you in advance.
