Android :Unable to instantiate activity ComponentInfo

Unable to instantiate activity ComponentInfo

You may be trying to find the view before onCreate() which is incorrect.

public class MainActivity extends Activity {

  ImageView mainImage = (ImageView) findViewById(R.id.imageViewMain); //incorrect

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