package com.example.itunes_mysia
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView
import androidx.recyclerview.widget.GridLayoutManager
import androidx.recyclerview.widget.RecyclerView
import androidx.viewpager.widget.ViewPager
import com.example.itunes_mysia.databinding.ActivityMainBinding
import com.google.android.material.tabs.TabLayout
import java.io.IOException
import java.nio.charset.Charset
class MainActivity : AppCompatActivity() {
private lateinit var itunesToolbar: androidx.appcompat.widget.Toolbar
private lateinit var itunesTabs: TabLayout
private lateinit var itunesTitleText: TextView
private lateinit var itunesViewPager: ViewPager
private lateinit var itunesPagerAdapters: PagerAdapters
private var artistName: ArrayList<String> = ArrayList()
var songName: ArrayList<String> = ArrayList()
var previewUrl: ArrayList<String> = ArrayList()
var artworkUrl60: ArrayList<String> = ArrayList()
var trackPrice: ArrayList<String> = ArrayList()
private lateinit var binding: ActivityMainBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
populateMusic()
// ***GETTING ERROR HERE***
val recyclerView = findViewById<RecyclerView>(R.id.recycler_view)
val mainActivity = this
recyclerView.apply {
layoutManager = GridLayoutManager(applicationContext, 1)
adapter = CardAdapter(musicList)
}
/** title = "KotlinApp"
val recyclerView = findViewById<RecyclerView>(R.id.recycler_view)
val linearLayoutManager = LinearLayoutManager(applicationContext)
recyclerView.layoutManager = linearLayoutManager
try {
val obj = JSONObject(loadJSONFromAsset())
val userArray = obj.getJSONArray("results")
for (i in 0 until userArray.length()) {
val songDetail = userArray.getJSONObject(i)
artistName.add(songDetail.getString("Artist Name"))
songName.add(songDetail.getString("Song Name"))
previewUrl.add(songDetail.getString("Song URL"))
artworkUrl60.add(songDetail.getString("Album Cover"))
trackPrice.add(songDetail.getString("Track Price"))
}
} catch (e: JSONException)
{
e.printStackTrace()
}
val customAdapter =
CustomAdapter(this@MainActivity, artistName, songName, previewUrl, artworkUrl60, trackPrice)
recyclerView.adapter = customAdapter **/
// Set find ID
itunesToolbar = findViewById(R.id.itunesToolbar)
itunesTitleText = findViewById(R.id.itunesTitleText)
itunesTabs = findViewById(R.id.itunesTabs)
itunesViewPager = findViewById(R.id.itunesViewPager)
itunesPagerAdapters = PagerAdapters(supportFragmentManager)
// Set Toolbar
itunesToolbar.setTitle("")
itunesTitleText.setText(getString(R.string.itunes))
setSupportActionBar(findViewById(R.id.itunesToolbar))
// Set Fragment List
itunesPagerAdapters.addfragment(RockFragment(), "Rock")
itunesPagerAdapters.addfragment(ClassicFragment(), "Classic")
itunesPagerAdapters.addfragment(PopFragment(), "Pop")
// Set View Pager Adapter
itunesViewPager.adapter = itunesPagerAdapters
// Set Tab Layout with View Pager Adapter
itunesTabs.setupWithViewPager(itunesViewPager)
// Set Icons
itunesTabs.getTabAt(0)!!.setIcon(R.mipmap.music1)
itunesTabs.getTabAt(1)!!.setIcon(R.mipmap.music2)
itunesTabs.getTabAt(2)!!.setIcon(R.mipmap.music3)
itunesTabs!!.addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
override fun onTabSelected(tab: TabLayout.Tab) {
itunesViewPager!!.currentItem = tab.position
}
override fun onTabUnselected(tab: TabLayout.Tab) {
}
override fun onTabReselected(tab: TabLayout.Tab) {
}
})
}
private fun populateMusic() {
val song1 = Music(
"Journey",
"Don't Stop Believin'",
"https://audio-ssl.itunes.apple.com/itunes-assets/AudioPreview125/v4/e4/6c/ad/e46cad13-317a-3074-8d0f-a41af0bb2437/mzaf_5207796602846861401.plus.aac.p.m4a",
R.drawable.song1,
1.99
)
musicList.add(song1)
}
private fun loadJSONFromAsset(): String {
val json: String?
try {
val inputStream = assets.open("rock.json")
val size = inputStream.available()
val buffer = ByteArray(size)
val charset: Charset = Charsets.UTF_8
inputStream.read(buffer)
inputStream.close()
json = String(buffer, charset)
return json
} catch (ex: IOException) {
ex.printStackTrace()
return ""
}
}
}
ERROR: 2022-08-11 08:59:29.090 4804-4804/com.example.itunes_mysia E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.itunes_mysia, PID: 4804 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.itunes_mysia/com.example.itunes_mysia.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3835) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4011) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2325) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:246) at android.app.ActivityThread.main(ActivityThread.java:8633) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager)' on a null object reference at com.example.itunes_mysia.MainActivity.onCreate(MainActivity.kt:40) at android.app.Activity.performCreate(Activity.java:8207) at android.app.Activity.performCreate(Activity.java:8191) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3808) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4011) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2325) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:246) at android.app.ActivityThread.main(ActivityThread.java:8633) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130)
CodePudding user response：
Try this
val recyclerView = findViewById<RecyclerView>(R.id.recycler_view)
recyclerView.layoutManager = GridLayoutManager(this, 1, GridLayoutManager.YOUR_ORIENTATION, false)
The error is caused because the app seems not to find the recyclerview or the layoutmanager is not properly set.
EDIT
After better looking at your code I saw you are using binding so .findViewById is not perfect, try using binding.recycler_view also
CodePudding user response：
wrong code, you use binding, so to access your recycler view just use:
binding.recyclerView
no need to use findViewById