如何解决LayoutInflaters上的NullPointerException？

分类：编程问答

如何解决如何解决LayoutInflaters上的NullPointerException？

我已经在这个问题上停留了一段时间，并且已经浏览了有关该问题的其他问题。但是，我不完全了解他们的解决方案以及如何将其应用于我的案件。

Logcat 

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.realtimechat/com.example.realtimechat.chats.ChatActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.LayoutInflater android.view.Window.getLayoutInflater()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3022)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3259)
        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$H.handleMessage(ActivityThread.java:1950)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7073)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.LayoutInflater android.view.Window.getLayoutInflater()' on a null object reference
        at android.app.Activity.getLayoutInflater(Activity.java:4435)
        at com.example.realtimechat.chats.ChatActivity.<init>(ChatActivity.kt:66)
        at java.lang.Class.newInstance(Native Method)
        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:69)
        at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1215)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3010)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3259) 
        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$H.handleMessage(ActivityThread.java:1950) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7073) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965) 

聊天活动 

package com.example.realtimechat.chats

import android.app.Activity
import android.content.Context
import android.content.Intent
import android.content.Intent.ACTION_PICK
import android.content.pm.PackageManager
import android.graphics.Bitmap
import android.net.Uri
import android.os.Bundle
import android.provider.MediaStore
import android.provider.MediaStore.ACTION_IMAGE_CAPTURE
import android.view.View
import android.view.inputmethod.InputMethodManager
import android.widget.EditText
import android.widget.ImageView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.core.app.ActivityCompat
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import androidx.swiperefreshlayout.widget.SwipeRefreshLayout
import com.example.realtimechat.R
import com.example.realtimechat.common.Constants
import com.example.realtimechat.common.Extras
import com.example.realtimechat.common.NodeNames
import com.example.realtimechat.common.Utils
import com.google.android.material.bottomsheet.BottomSheetDialog
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.database.*
import com.google.firebase.storage.FirebaseStorage
import java.io.ByteArrayInputStream
import java.io.ByteArrayOutputStream


class ChatActivity : AppCompatActivity(),View.OnClickListener {

    private lateinit var etMessage: EditText
    private lateinit var ivSend: ImageView
    private lateinit var ivAttachment: ImageView

    private lateinit var mAuth: FirebaseAuth
    private lateinit var mRootRef: DatabaseReference

    private lateinit var currentUserId: String
    private lateinit var chatUserId: String

    private lateinit var rvMessages: RecyclerView
    private lateinit var srlMessages: SwipeRefreshLayout
    private lateinit var messagesAdapter: MessagesAdapter
    private lateinit var messagesList: MutableList<MessageModel>

    private var currentPage = 1
    companion object {
        private const val RECORD_PER_PAGE = 30
    }

    private val REQUEST_CODE_CAPTURE_IMAGE=102
    private val REQUEST_CODE_PICK_IMAGE=101
    private val REQUEST_CODE_PICK_VIDEO=103

    private lateinit var databaseReferenceMessages: DatabaseReference
    private lateinit var childEventListener: ChildEventListener

    private lateinit var bottomSheetDialog: BottomSheetDialog
    val view: View = layoutInflater.inflate(R.layout.chat_file_options,null)

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_chat)

        etMessage = findViewById(R.id.etMessage)
        ivSend = findViewById(R.id.ivSend)
        ivAttachment = findViewById(R.id.ivAttachment)

        ivSend.setOnClickListener(this)
        ivAttachment.setOnClickListener(this)

        mAuth = FirebaseAuth.getInstance()
        mRootRef = FirebaseDatabase.getInstance().reference

        currentUserId = mAuth.currentUser!!.uid

        if(intent.hasExtra(Extras.USER_KEY)){
            chatUserId = intent.getStringExtra(Extras.USER_KEY)!!
        }

        rvMessages = findViewById(R.id.rvMessages)
        srlMessages = findViewById(R.id.srlMessages)

        val layoutManager = LinearLayoutManager(applicationContext)
        layoutManager.orientation = RecyclerView.VERTICAL
        rvMessages.layoutManager = layoutManager
        rvMessages.setHasFixedSize(true)

        messagesList = ArrayList()
        messagesAdapter = MessagesAdapter(this,messagesList)
        rvMessages.adapter = messagesAdapter

        loadMessages()
        rvMessages.scrollToPosition(messagesList.size-1)

        srlMessages.setOnRefreshListener(object: SwipeRefreshLayout.OnRefreshListener{
            override fun onRefresh() {
                currentPage++
                loadMessages()
            }

        })

        bottomSheetDialog = BottomSheetDialog(this)
        view.findViewById<View>(R.id.llCamera).setOnClickListener(this)
        view.findViewById<View>(R.id.llGallery).setOnClickListener(this)
        view.findViewById<View>(R.id.llVideo).setOnClickListener(this)
        view.findViewById<View>(R.id.ivClose).setOnClickListener(this)
        bottomSheetDialog.setContentView(view)
    }

    //send messages
    private fun sendMessage(msg: String,msgType: String,pushId: String){
        try {
            if (msg != "") {
                val messageMap = HashMap<Any,Any>()
                messageMap[NodeNames.MESSAGE_ID] = pushId
                messageMap[NodeNames.MESSAGE] = msg
                messageMap[NodeNames.MESSAGE_TYPE] = msgType
                messageMap[NodeNames.MESSAGE_FROM] = currentUserId
                messageMap[NodeNames.MESSAGE_TIME] = ServerValue.TIMESTAMP

                val currentUserRef = NodeNames.MESSAGES + "/" + currentUserId + "/" + chatUserId
                val chatUserRef = NodeNames.MESSAGES + "/" + chatUserId + "/" + currentUserId

                val messageUserMap = mutableMapOf<String,Any>()
                messageUserMap["$currentUserRef/$pushId"] = messageMap
                messageUserMap["$chatUserRef/$pushId"] = messageMap

                etMessage.setText("")

                mRootRef.updateChildren(messageUserMap,object : DatabaseReference.CompletionListener {
                    override fun onComplete(databaseError: DatabaseError?,databaseReference: DatabaseReference) {
                        if (databaseError != null) {
                            Toast.makeText(applicationContext,"Failed to send message: ${databaseError.message}",Toast.LENGTH_SHORT).show()
                        }
                        run{
                            Toast.makeText(applicationContext,"Message sent successfully!",Toast.LENGTH_SHORT).show()
                        }
                    }
                })
            }
        } catch (e: Exception) {
            Toast.makeText(applicationContext,"Failed to send message: ${e.localizedMessage}",Toast.LENGTH_SHORT).show()
        }
    }

    private fun loadMessages(){
        messagesList.clear()
        databaseReferenceMessages = mRootRef.child(NodeNames.MESSAGES).child(currentUserId).child(chatUserId)

        val messageQuery: Query = databaseReferenceMessages.limitToLast(currentPage * RECORD_PER_PAGE)

        childEventListener = object: ChildEventListener{
            override fun onChildAdded(snapshot: DataSnapshot,previousChildName: String?) {
                val message: MessageModel = snapshot.getValue(MessageModel::class.java)!!

                messagesList.add(message)
                messagesAdapter.notifyDataSetChanged()

                rvMessages.scrollToPosition(messagesList.size-1)
                srlMessages.isRefreshing = false
            }

            override fun onChildChanged(snapshot: DataSnapshot,previousChildName: String?) {
            }

            override fun onChildRemoved(snapshot: DataSnapshot) {
            }

            override fun onChildMoved(snapshot: DataSnapshot,previousChildName: String?) {
            }

            override fun onCancelled(error: DatabaseError) {
                srlMessages.isRefreshing = false
            }
        }

        messageQuery.addChildEventListener(childEventListener)
    }

    private fun uploadFile(uri: Uri,messageType: String){
        val databaseReference = mRootRef.child(NodeNames.MESSAGES).child(currentUserId).child(chatUserId).push()
        val pushId = databaseReference.key!!

        val folderName =
            if (messageType == Constants.MESSAGE_TYPE_VIDEO) Constants.MESSAGE_VIDEOS else Constants.MESSAGE_IMAGES
        val fileName: String =
            if (messageType == Constants.MESSAGE_TYPE_VIDEO) "$pushId.mp4" else "$pushId.jpg"

        val storageReference = FirebaseStorage.getInstance().reference
        val fileReference = storageReference.child(folderName).child(fileName)
        fileReference.putFile(uri)
    }

    private fun uploadBytes(bytes: ByteArrayOutputStream,messageType: String){
        val databaseReference = mRootRef.child(NodeNames.MESSAGES).child(currentUserId).child(chatUserId).push()
        val pushId = databaseReference.key!!

        val folderName =
            if (messageType == Constants.MESSAGE_TYPE_VIDEO) Constants.MESSAGE_VIDEOS else Constants.MESSAGE_IMAGES
        val fileName: String =
            if (messageType == Constants.MESSAGE_TYPE_VIDEO) "$pushId.mp4" else "$pushId.jpg"

        val storageReference = FirebaseStorage.getInstance().reference
        val fileReference = storageReference.child(folderName).child(fileName)
        fileReference.putBytes(bytes.toByteArray())
    }

    //if any objects are clicked
    override fun onClick(v: View?) {
        when(v!!.id){
            R.id.ivSend -> {
                val utility = Utils()
                if(utility.connectionAvailable(this)) {
                    val message = etMessage.text.toString().trim()

                    val messageType = NodeNames.MESSAGE_TYPE_TEXT

                    val userMessagePush =
                        mRootRef.child(NodeNames.MESSAGES).child(currentUserId).child(chatUserId)
                            .push()
                    val pushId = userMessagePush.key

                    sendMessage(message,messageType,pushId!!)
                }else{
                    Toast.makeText(applicationContext,"No Internet connection available",Toast.LENGTH_SHORT).show()
                }
            }
            R.id.ivAttachment -> {
                if(ActivityCompat.checkSelfPermission(this,android.Manifest.permission.READ_EXTERNAL_STORAGE)==PackageManager.PERMISSION_GRANTED){
                    if(bottomSheetDialog!=null){
                        bottomSheetDialog.show()
                    }
                }else{
                    ActivityCompat.requestPermissions(this,arrayOf(android.Manifest.permission.READ_EXTERNAL_STORAGE),1)
                }

                val inputMethodManager = getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
                if(inputMethodManager!=null){
                    inputMethodManager.hideSoftInputFromWindow(view.windowToken,0)
                }
            }
            R.id.llCamera -> {
                bottomSheetDialog.dismiss()
                val intentCamera = Intent(ACTION_IMAGE_CAPTURE)
                startActivityForResult(intentCamera,REQUEST_CODE_CAPTURE_IMAGE)
            }
            R.id.llGallery -> {
                bottomSheetDialog.dismiss()
                val intentImage = Intent(ACTION_PICK,MediaStore.Images.Media.EXTERNAL_CONTENT_URI)
                startActivityForResult(intentImage,REQUEST_CODE_PICK_IMAGE)
            }
            R.id.llVideo -> {
                bottomSheetDialog.dismiss()
                val intentVideo = Intent(ACTION_PICK,MediaStore.Video.Media.EXTERNAL_CONTENT_URI)
                startActivityForResult(intentVideo,REQUEST_CODE_PICK_VIDEO)
            }
        }
    }

    override fun onActivityResult(requestCode: Int,resultCode: Int,data: Intent?) {
        super.onActivityResult(requestCode,resultCode,data)

        if(resultCode== Activity.RESULT_OK){
            if(requestCode==REQUEST_CODE_CAPTURE_IMAGE) {
                val bitMap = data!!.extras!!.get("data") as Bitmap

                val bytes = ByteArrayOutputStream()
                bitMap.compress(Bitmap.CompressFormat.JPEG,100,bytes)
                uploadBytes(bytes,Constants.MESSAGE_TYPE_IMAGE)
            }else if(requestCode==REQUEST_CODE_PICK_IMAGE){
                val uri = data!!.data!!
                uploadFile(uri,Constants.MESSAGE_TYPE_IMAGE)
            }else if(requestCode==REQUEST_CODE_PICK_VIDEO){
                val uri = data!!.data!!
                uploadFile(uri,Constants.MESSAGE_TYPE_VIDEO)
            }
        }
    }

    override fun onRequestPermissionsResult(requestCode: Int,permissions: Array<out String>,grantResults: IntArray) {
        super.onRequestPermissionsResult(requestCode,permissions,grantResults)
        if(requestCode==1){
            if(grantResults.size>1 && grantResults[0]==PackageManager.PERMISSION_GRANTED){
                if(bottomSheetDialog!=null){
                    bottomSheetDialog.show()
                }
            }else{
                Toast.makeText(this,"Permission needed",Toast.LENGTH_SHORT).show()
            }
        }
    }
}

如果任何人都可以（轻松地）解释如何解决和解决这些类型的问题以及如何解决我的情况，将不胜感激！

解决方法

layoutInflater尚未实例化。对视图执行任何操作时，您几乎必须等到onCreate方法。像这样：

var view: View? = null
// OR
lateinit var view: View

override fun onCreate(savedInstanceState: Bundle?) {
   super.onCreate(savedInstanceState)
   setContentView(R.layout.activity_chat)

   view = layoutInflater.inflate(R.layout.chat_file_options,null)
   ......
}

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