Kotlin array of buttons are all null

Question

Creating an array of buttons

    val buttons = arrayOf(spot0, spot1, spot2, spot3, spot4, spot5, spot6)
    Log.v("array", "spot0=" + buttons[0])

    images.shuffle()
    val randomnumber = (0..5).random()

    buttons[0].setBackgroundResource(images[randomnumber])

Gets this error message:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageButton.setBackgroundResource(int)' on a null object reference

and this log output:

V/array: spot0=null

This is Kotlin so I shouldn't have to call findViewById from what I can tell.

apply plugin: 'kotlin-android-extensions' is added to my build.gradle

Button is setup in xml:

<ImageButton
    android:id="@+id/spot0"
    android:text="zero"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="131dp"
    android:layout_marginLeft="131dp"
    android:layout_marginTop="16dp"
    android:layout_marginEnd="131dp"
    android:layout_marginRight="131dp"
    android:background="@drawable/heart"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.565"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

I'm attempting to randomize my button images and attempting to do it via an array. How can I go about this?

Make sure your code is inside onCreate method. If you try to initialize the buttons array before onCreate then it will cause some problem.. — towhid
– towhid, Commented Jun 11, 2020 at 19:53
The first usage of the array in my code is what is above, but it didn't copy paste over all the text. I am not initializing it anywhere else. It is in onCreate. The full text is: val buttons :Array<ImageButton!> = arrayOf(spot0, spot1, spot2, spot3, spot4, spot5, spot6) — Siobhan S
– Siobhan S, Commented Jun 11, 2020 at 20:00
val buttons = arrayOf(spot0, spot1, spot2, spot3, spot4, spot5, spot6) buttons[0] = spot0 Log.v("array", "spot0=" + buttons[0]) That still outputs a null in the log. — Siobhan S
– Siobhan S, Commented Jun 11, 2020 at 20:04
Do you call setContentView(R.id.your_layout) method before initializing the array? — Sergio
– Sergio, Commented Jun 11, 2020 at 20:06

Sergio · Accepted Answer · 2020-06-11 20:13:52Z

1

If you are in `Activity`:

You should call setContentView(R.id.your_layout) method in Activity's onCreate() method before accessing the views and initializing the array.

If you are in `Fragment`:

Try to access the views and initialize the array in onViewCreated() method.

edited Jun 11, 2020 at 20:13

answered Jun 11, 2020 at 20:09

Sergio

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4 Comments

Siobhan S Over a year ago

I'm in onCreate(). setContentView returns the error: "Unresolved reference: setContentView" setContentView works fine in the MainActivity.kt but it isn't working in this fragment class that I'm working in.

Sergio Over a year ago

@SiobhanS I've edited my answer. Try to do your things in onViewCreated() method.

Siobhan S Over a year ago

Yes! This worked! Thank you!!! I moved the code to onViewCreated() and it worked perfectly.

Sergio Over a year ago

great. that's because in Fragment's onCreate method the layout is not set and views are not initialized yet.

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