Null pointer exception in Android caused by a button

Question

My Activity class looks like that:

public class FullscreenActivity extends AppCompatActivity {
    private Button btnTakePhoto = new Button(this);
    private Button btnRecordVideo = new Button(this);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fullscreen);

        btnTakePhoto = (Button) findViewById(R.id.btnTakePhoto);
        btnTakePhoto.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                helloWorldKamera();
            }
        });
    }

    public void helloWorldKamera() {
        System.out.println("Kamera");
    }

}

My activity_fullscreen.xml file looks like that:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffffff">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <Button
            android:text="Foto"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="0.5"
            android:id="@+id/btnTakePhoto" />

        <Button
            android:text="Video"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="0.5"
            android:id="@+id/btnRecordVideo"
            />
    </LinearLayout>
</FrameLayout>

Now I get the following error:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference.
Do you know how to fix the null pointer exception? I don't know why my button is null.
Is it right how I initialize the button or is the error caused by findViewById?

score 0 · Answer 1 · answered Oct 24 '16 at 15:40

0

Replace

  private Button btnTakePhoto = new Button(this);

by

private Button btnTakePhoto;

answered Oct 24 '16 at 15:40

Ganesh Pokale

1,538
1
14
28

Will Evers · Answer 2 · 2016-10-24T15:45:14.283

0

You you can't set you buttons to new Button(this). It will likely always be null, if not incorrect. I would define your button in the onCreate method only, then set it to the necessary id.

To answer your question specifically, the findViewById part of your code is correct. You just messed up the definition of your Button variables

edited Oct 24 '16 at 15:45

answered Oct 24 '16 at 15:43

Will Evers

934
9
17

but removing the `new Button(this)` also doesn't work – mafioso Oct 24 '16 at 15:44
you should define you button in the method. – Will Evers Oct 24 '16 at 15:46
I'd guess its a different null pointer caused by two lines above your super.onCreate() – Will Evers Oct 24 '16 at 15:48

Null pointer exception in Android caused by a button

2 Answers2