I am stuck on this and I would like a help from you you guys

Question

1.00/5 (1 vote)

See more:

when i run the code the debug shows me this:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.intskot, PID: 18308
    java.lang.NullPointerException
        at com.example.intskot.fragments.PostsDetailsFragment$retrievePosts$1.onDataChange(PostDetailsFragment.kt:68)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)
        at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
        at android.os.Handler.handleCallback(Handler.java:907)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7478)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:549)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:941)

the code to this is this:

package com.example.intskot.fragments

import android.content.Context
import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.intskot.adapter.PostAdapter
import com.example.intskot.Model.Post
import com.example.intskot.R
import com.google.firebase.database.DataSnapshot
import com.google.firebase.database.DatabaseError
import com.google.firebase.database.FirebaseDatabase
import com.google.firebase.database.ValueEventListener

class PostsDetailsFragment : Fragment() {

    private var postAdapter: PostAdapter? = null
    private var  postList: MutableList<Post>? = null
    private var postId: String = ""


    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        val view =  inflater.inflate(R.layout.fragment_post_details, container, false)

        val preferences = context?.getSharedPreferences("PREFS", Context.MODE_PRIVATE)
        if (preferences!= null)
        {
            postId = preferences.getString("PostId", "none")!!
        }

        var recyclerView: RecyclerView
        recyclerView = view.findViewById(R.id.recycler_view_post_details)
        recyclerView.setHasFixedSize(true)
        val linearLayoutManager = LinearLayoutManager(context)
        recyclerView.layoutManager = linearLayoutManager

        postList = ArrayList()
        postAdapter = context?.let { PostAdapter(it, postList as ArrayList<Post>) }
        recyclerView.adapter = postAdapter

        retrievePosts()

        return view
    }


    private fun retrievePosts() {
        val postsRef = FirebaseDatabase.getInstance().reference
            .child("Posts")
            .child(postId)

        postsRef.addValueEventListener(object : ValueEventListener
        {
            override fun onDataChange(p0: DataSnapshot)
            {
                postList?.clear()

                val post = p0.getValue(Post::class.java)

                postList!!.add(post!!)

                postAdapter!!.notifyDataSetChanged()
            }

            override fun onCancelled(p0: DatabaseError) {

            }
        })
    }
}

any help?

What I have tried:

the problem is at the nullpointerExeption of

postList!!.add(post!!)

but when i ran the code the app crash

Posted 6-Oct-20 22:17pm

Orestis Tsanakas

Updated 7-Oct-20 0:40am

Add a Solution

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Accepted Answer · 2020-10-06T22:52:00

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

Sandeep Mewara · Accepted Answer · 2020-10-07T00:41:00

You know the line and the error.

Quote:
postList!!.add(post!!)

You use !! operator. !! will throw NullPointerException if the value is null.

With !!, if postList is null OR post is null, it will raise the error.

Look at the reason, handle the same. Given you used operator !!, I am assuming you wrote it for a reason and want a NullPointerException to be raised. If you got this code from elsewhere and intention is to check for null, do that.

Reference: Null Safety - Kotlin Programming Language[^]

Quote:
the not-null assertion operator (!!) converts any value to a non-null type and throws an exception if the value is null. We can write b!!, and this will return a non-null value of b (e.g., a String in our example) or throw an NPE if b is null: val l = b!!.length

I am stuck on this and I would like a help from you you guys

2 solutions

Solution 1

Solution 2

Add your solution here

Preview 0