Is there a way of knowing how a view is null, even though it was declared and called?

Question

EDIT Ok guys, I was literally trying to call the FAB which is inside the fragment_home, in another fragment, my mistake, I should've called inside the Homefragment, I just changed it and it works now, thank you to everyone that help.

TO ANYONE THAT GETS THE SAME ERROR -Check if you declared the ID of the view well -Check if you are inside that activity class (activity_main.xml -> MainActivity.kt) -Call the view correctly. IF that doesn't solve it, you will find great answers down below, good luck.

I have this fab, declared here:

<?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=".BaseFragment"
    android:background="@color/darkBlack">

    <TextView
        android:id="@+id/my_notes"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:fontFamily="sans-serif-black"
        android:text="@string/notes"
        android:textColor="@color/white"
        android:textSize="@dimen/_20sdp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


    <androidx.appcompat.widget.SearchView
        android:id="@+id/search_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:searchIcon="@drawable/ic_search"
        android:background="@drawable/background"
        app:queryHint="Search..."
        app:defaultQueryHint="Search..."
        android:theme="@style/ThemeOverlay.search"
        android:iconifiedByDefault="false"
        app:layout_constraintTop_toBottomOf="@+id/my_notes"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_margin="10dp"
        />


    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/_10sdp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/search_view" />

    <LinearLayout
        android:id="@+id/linearLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/darkBlack"
        android:orientation="horizontal"
        android:padding="@dimen/_10sdp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent">

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/ic_baseline_check_24"
            app:tint="@color/white" />

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="@dimen/_10sdp"
            android:src="@drawable/ic_image"
            app:tint="@color/white" />

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="@dimen/_10sdp"
            android:src="@drawable/ic_baseline_insert_link_24"
            app:tint="@color/white" />

    </LinearLayout>


    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@color/yellow"
        android:id="@+id/fabBtnCreateNote"
        android:tint="@color/yellow"
        android:layout_marginEnd="@dimen/_20sdp"
        android:layout_marginBottom="@dimen/_20sdp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:src="@drawable/ic_add"
        android:contentDescription="Fab" />

</androidx.constraintlayout.widget.ConstraintLayout>

I am calling it here:

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import com.google.android.material.floatingactionbutton.FloatingActionButton
import kotlinx.android.synthetic.main.fragment_home.*
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.Job
import kotlin.coroutines.CoroutineContext

abstract class BaseFragment() : Fragment(), CoroutineScope {

    private lateinit var job: Job
    override val coroutineContext: CoroutineContext
        get() = job +Dispatchers.Main

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.fragment_home, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        var fab = view.findViewById<FloatingActionButton>(R.id.fabBtnCreateNote)

        //Line throwing the error ->
        fab.setOnClickListener{
            replaceFragment(CreateNoteFragment.newInstance(), true)
        }
    }


    open fun replaceFragment(fragment: Fragment, istransition:Boolean) {
        val fragmentTransition = activity!!.supportFragmentManager.beginTransaction()

        if(istransition) {
            fragmentTransition.setCustomAnimations(android.R.anim.slide_out_right, android.R.anim.slide_in_left)
        }

        fragmentTransition.add(R.id.frame_layout, fragment).addToBackStack(fragment.javaClass.simpleName).commit()
    }
}

I have declared it and am know calling it (I have android-kotlin-extensions) but it is throwing me a null object error:

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.floatingactionbutton.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

It is pointing to the fabBtnCreateNote.setOnClickListener{} line.

I am not understanding what this means, could anyone help me out?

Answer 1

Try using the "findViewById" function like in this answer:

Android setOnClickListener method - How does it work?

I haven't done this stuff in a while, but I think the @id attribute only creates a string id which you have to access through R. and use to return the actual view.

EDIT: responding to your edit: You have to do:

var fabBtnCreateNote = view.findViewById<FloatingActionButton>(R.id.fabBtnCreateNote)

Answer 2

var fab = fabBtnCreateNote.findViewById<FloatingActionButton>(R.id.fabBtnCreateNote)

This is getting closer. However, you probably still get a NPE because fabBtnCreateNote is null. Instead, try this:

var fabBtnCreateNote = view.findViewById<FloatingActionButton>(R.id.fabBtnCreateNote)

Note that you need to call findViewById() with view because this is the parent which contains the FAB.

Now that fabBtnCreateNote has a valid reference to the FAB view object, you can call methods on it, such as setOnClickListener().

Answer 3

If you specifically want to use synthetics, you can consider this:

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    return inflater.inflate(R.layout.your_fragment, container, false)
}

then use

  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        yourButton.whatever
    }

---

because onCreateView occurs before onViewCreated, so inside onViewCreated you can access your button

Answer 4

ANSWER

Ok guys, I was literally trying to call the FAB which is inside the fragment_home, in another fragment, my mistake, I should've called inside the Homefragment, I just changed it and it works now, thank you to everyone that help.

TO ANYONE THAT GETS THE SAME ERROR

• Check if you declared the ID of the view well
• Check if you are inside that activity class (activity_main.xml -> MainActivity.kt)
• Call the view correctly.

IF that doesn't solve it, you will find great answers down below, good luck.

Consider reading:

Android setOnClickListener method - How does it work?