RadioButton setChecked NullPointerException

Question

I don't get this to work and I don't see why.

 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RadioButton.setChecked(boolean)' on a null object reference
        at eu.twenty1media.snakeplus.fragment.MainFragment.onCreateView(MainFragment.java:48)

    String lastlevel = msettings.getLevel();
    Log.d("MainFragment.java", "Last level from Database: radio"+lastlevel);

    RadioGroup rLevelGroup = (RadioGroup) getActivity().findViewById(R.id.radioLevel);
    int resourceId = this.getResources().getIdentifier("radio"+lastlevel, "id", getActivity().getPackageName());

    //rLevelGroup.check(R.id.radioextreme); //Nullpointer!

    //RadioButton levelbtn = (RadioButton) getActivity().findViewById(R.id.radioextreme); //NULLPOINTER
    //levelbtn.setChecked(true);

I tried both methods at the bottom, but none of them seems to work, I always get a NPE. I tried using the resourceId String but as you can see a normal resource id aswell.

    <RadioGroup
    android:id="@+id/radioLevel"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:orientation="horizontal"
    android:layout_marginBottom="16dp"
    android:gravity="center">
    <RadioButton
        android:layout_width="90dp"
        android:layout_height="wrap_content"
        android:id="@+id/radionormal"
        android:text="@string/level_normal"
        android:background="@drawable/radiolevel"
        android:button="@android:color/transparent"
        android:paddingLeft="8dp"
        android:paddingRight="8dp"
        android:paddingTop="4dp"
        android:paddingBottom="4dp"
        android:layout_marginRight="2dp"
        android:layout_marginLeft="2dp"

        android:gravity="center"
        android:textColor="@color/orange_1"
        android:textStyle="bold"
        />
    <RadioButton
        android:layout_width="90dp"
        android:layout_height="wrap_content"
        android:id="@+id/radiohard"
        android:background="@drawable/radiolevel"
        android:button="@android:color/transparent"
        android:text="@string/level_hard"
        android:paddingLeft="8dp"
        android:paddingRight="8dp"
        android:paddingTop="4dp"
        android:paddingBottom="4dp"
        android:layout_marginRight="2dp"
        android:layout_marginLeft="2dp"
        android:gravity="center"
        android:textColor="@color/orange_1"
        android:textStyle="bold"
        />
    <RadioButton
        android:layout_width="90dp"
        android:layout_height="wrap_content"
        android:id="@+id/radioextreme"
        android:background="@drawable/radiolevel"
        android:button="@android:color/transparent"
        android:text="@string/level_extreme"
        android:paddingLeft="8dp"
        android:paddingRight="8dp"
        android:paddingTop="4dp"
        android:paddingBottom="4dp"
        android:layout_marginRight="2dp"
        android:layout_marginLeft="2dp"
        android:gravity="center"
        android:textColor="@color/orange_1"
        android:textStyle="bold"
        />
    </RadioGroup>

Thanks for the help.

EDIT1: With commenting the Lines below i don't get a Nullpointer Exception.

Answer 1

If it is an an activity:

RadioButton levelbtn = (RadioButton) findViewById(R.id.radioextreme); 
levelbtn.setChecked(true);

If it is in a fragment.

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.page_two, container, false);
    RadioButton levelbtn = (RadioButton) v.findViewById(R.id.radioextreme); 
    levelbtn.setChecked(true);
    return v;
}

You can also set a radio button checked within the XML

<RadioButton
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:checked="true"
    android:id="@+id/radioButton" />