Force Close "FATAL EXCEPTION" & "findViewById(com.google.…aterial.R.id.coordinator) must not be null" Kotlin

Question

I try to open new activity from bottomnavbar, but my app force close at first time when i open it, and this is the error message i get.

please someone help me, and thanks for your help.

Error Code

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.apps.test.fx, PID: 24187
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.apps.test.fx/com.apps.test.fx.Dashboard}:

java.lang.NullPointerException: findViewById(com.google.…aterial.R.id.coordinator) must not be null

Kotlin Code

private lateinit var chipNavigationBar: ChipNavigationBar
private lateinit var constraint: CoordinatorLayout


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


    val window = window
    window.decorView.systemUiVisibility = View.SYSTEM_UI_FLAG_FULLSCREEN
    constraint = findViewById(com.google.android.material.R.id.coordinator)

    chipNavigationBar = findViewById(R.id.chip_app_bar)
    chipNavigationBar.setItemSelected(R.id.home, true)
    supportFragmentManager.beginTransaction().replace(R.id.root_layout, home_fragment()).commit()

    constraint.setBackgroundColor(getColor(R.color.dk_purple))

    bottom_menu()}

    private fun bottom_menu() {
        chipNavigationBar.setOnItemSelectedListener({
            when(it){
                R.id.home ->{
                    constraint.setBackgroundColor(getColor(R.color.dk_purple))
                    supportFragmentManager.beginTransaction().replace(R.id.root_layout, home_fragment()).commit()
                }

                R.id.promo ->{
                    constraint.setBackgroundColor(getColor(R.color.sft_purple))
                    supportFragmentManager.beginTransaction().replace(R.id.root_layout, home_fragment()).commit()

                }

            }
        })
    }

fun floating_button(view: View){
    constraint.setBackgroundColor(getColor(R.color.purple_500))
    supportFragmentManager.beginTransaction().replace(R.id.root_layout, home_fragment()).commit()

    chipNavigationBar.setItemSelected(R.id.home, true)

    val int = Intent(this, floating_action::class.java)
    startActivity(int)
}

XMLCode

<com.google.android.material.floatingactionbutton.FloatingActionButton
    android:onClick="floating_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:maxImageSize="30dp"
    android:layout_marginBottom="40dp"
    android:backgroundTint="@color/white"
    app:layout_anchor="@id/bottom_app_bar"
    android:src="@drawable/ic_category" />

<com.google.android.material.bottomappbar.BottomAppBar
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/bottom_app_bar"
    android:layout_gravity="bottom"
    android:backgroundTint="@color/dk_green"
    style="@style/Widget.MaterialComponents.BottomNavigationView.Colored"
    app:fabCradleMargin="6dp"
    app:fabAlignmentMode="center"
    app:fabCradleRoundedCornerRadius="50dp">

    <com.ismaeldivita.chipnavigation.ChipNavigationBar
        android:id="@+id/chip_app_bar"
        android:layout_gravity="fill_horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@android:color/transparent"
        android:padding="10dp"
        app:cnb_iconSize="30dp"
        android:layout_marginEnd="16dp"
        app:cnb_menuResource="@menu/item_menu"
        app:cnb_unselectedColor="@color/white" />

</com.google.android.material.bottomappbar.BottomAppBar>

Answer 1

Here's the error in your stacktrace (each error is caused by the one below, so the last one is the source of the problem):

Caused by: java.lang.NullPointerException: findViewById(com.google.…aterial.R.id.coordinator) must not be null

It's saying that findViewById call is returning null, when it's not allowed to be null. It's not allowed because you're assigning it to constraint, which is defined as a non-null type:

private lateinit var constraint: CoordinatorLayout

If null was allowed it would be ConstraintLayout? instead. findViewById returns null if it can't find a view with the provided ID in the view hierarchy you're doing the lookup on, i.e. the activity's layout you're inflating in setContentView.

---

So R.layout.activity_dashboard doesn't have a CoordinatorLayout (or any View) with an ID of com.google.android.material.R.id.coordinator. And looking at your XML, that's true! So you need to add one:

    <androidx.coordinatorlayout.widget.CoordinatorLayout
            android:id="@+id/coordinator"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_constraintBottom_toBottomOf="parent">

That gives you a resource ID of R.id.coordinator. Any layouts you're creating should have IDs in the R.id. namespace, not android.anything.else.:

constraint = findViewById(R.id.coordinator)

You should only need to access android.R.id... if you're using system-provided layouts like android.R.layout.simple_list_item (or whatever it is) or components like the standard app bar (where the home button has an android.R.id. ID)