no errors but still app force closes in android studio

Question

I am trying to make an app to take an image when the button is clicked and then take that image and place it in the image view field. The given code is fine with no errors, i have checked many times. Still i get this error of runtime exception even when i have instanciated the activity in the manifest file.

here is xml code:

<LinearLayout 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"
    android:orientation="vertical"
    android:weightSum="10"
    tools:context="com.example.android.tryingcamera.MainActivity">
<ImageView
    android:id="@+id/imageView"
    android:layout_width="wrap_content"
    android:layout_height="fill_parent"
    android:layout_weight="9"/>
<Button
    android:id="@+id/btnCamera"
    android:layout_weight="1"
    android:text="Tap To Open Camera"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="btncameraClicked"/>

here is java code:

public class MainActivity extends AppCompatActivity {

private ImageView imageview=(ImageView)findViewById(R.id.imageView);
private Button btncamera = (Button) findViewById(R.id.btnCamera);
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}



public void btncameraClicked(View view){
    Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    startActivityForResult(intent,0);
}

@Override
protected void onActivityResult(int requestCode,int resultCode,Intent data ){
    super.onActivityResult(requestCode,resultCode,data);
    Bitmap bitmap=(Bitmap)data.getExtras().get("data");
    imageview.setImageBitmap(bitmap);
}

}

The logcat show this:

Process: com.example.android.tryingcamera, PID: 27769
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.tryingcamera/com.example.android.tryingcamera.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2567)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6119)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:117)
    at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:149)
    at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:29)
    at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:54)
    at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:31)
    at android.support.v7.app.AppCompatDelegateImplN.<init>(AppCompatDelegateImplN.java:31)
    at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:198)
    at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:183)
    at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
    at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
    at com.example.android.tryingcamera.MainActivity.<init>(MainActivity.java:14)
    at java.lang.Class.newInstance(Native Method)
    at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2557)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6119) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at 

com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

you can't call `findViewById` before calling `setContentView` — Vladyslav Matviienko, May 04 '18 at 08:46
Required run time permission if u using Android marshmallow or later versions.. — NagarjunaReddy, May 04 '18 at 08:50

AskNilesh · Answer 1 · 2018-05-04T08:55:57.400

Check your code You need to Do findViewById() inside your onCreate() method after setContentView()

Try this Change your code like below code

 public class MainActivity extends AppCompatActivity {

    private ImageView;
    private Button ;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        imageview=(ImageView)findViewById(R.id.imageView);
        btncamera = (Button) findViewById(R.id.btnCamera);
    }



    public void btncameraClicked(View view){
        Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        startActivityForResult(intent,0);
    }

    @Override
    protected void onActivityResult(int requestCode,int resultCode,Intent data ){
        super.onActivityResult(requestCode,resultCode,data);
        Bitmap bitmap=(Bitmap)data.getExtras().get("data");
        imageview.setImageBitmap(bitmap);
    }

}

Thanks, it worked. But also u could explain why the code before this didnt work as expected?? — Shiv Mistry, May 04 '18 at 09:15
@ShivMistry yopu need to do findViewById() inside your onCreate() method after setContentView() — AskNilesh, May 04 '18 at 09:16

score 0 · Answer 2 · answered May 04 '18 at 08:52

When you declare imageview and btnamera as class variables and assign it all using findViewById, the findViewById method called when the instance of MainActivity class created, but the view not ready.

you can assign the variables after the view already set.

private ImageView imageview;
private Button btncamera;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    imageview=(ImageView)findViewById(R.id.imageView);
    btncamera = (Button) findViewById(R.id.btnCamera);
}

no errors but still app force closes in android studio

2 Answers2