My Android App consists of a Main Activity which switches through various Fragements. When I try to find 9 buttons from the layout file by id in order to add them to an Button Array and later give them an onClickEventListener, I get an exception, that the found buttons are null even though I have defined those id's
// Java code of the Main Activity
public class MainActivity extends AppCompatActivity implements Welcome.OnFragmentInteractionListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Welcome welcomeFragment = Welcome.newInstance("", "");
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.add(R.id.parent_layout, welcomeFragment);
fragmentTransaction.commit();
}
@Override
public void onChangeToMode() {
replaceFragment(Mode.newInstance("", ""), "MODE");
}
public void onPvpButtonClicked(View view) {
replaceFragment(Pvp.newInstance("", ""), "PVP");
}
public void onPvcButtonClicked(View view) {
replaceFragment(Welcome.newInstance("", ""), "WELCOME");
}
public void onPvc2ButtonClicked(View view) {
replaceFragment(Welcome.newInstance("", ""), "WELCOME");
}
private void replaceFragment(Fragment fragment, String tag) {
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.parent_layout, fragment);
fragmentTransaction.addToBackStack(tag);
fragmentTransaction.commit();
}
}
// Layout of the Tic Tac Toe fragment
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1">
<Button
android:id="@+id/button_00"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:textSize="60sp"/>
<Button
android:id="@+id/button_01"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:textSize="60sp"/>
<Button
android:id="@+id/button_02"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:textSize="60sp"/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1">
<Button
android:id="@+id/button_10"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:textSize="60sp"/>
<Button
android:id="@+id/button_11"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:textSize="60sp"/>
<Button
android:id="@+id/button_12"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:textSize="60sp"/>
</LinearLayout>
//etc.
</LinearLayout>
</LinearLayout>
// Java Code of the Tic Tac Toe fragment
public class Pvp extends Fragment implements View.OnClickListener {
// UI deklarieren
private Button[][] buttons = new Button[3][3];
private boolean player1Turn = true;
private int roundCount;
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
public Pvp() {
// Required empty public constructor
}
// TODO: Rename and change types and number of parameters
public static Pvp newInstance(String param1, String param2) {
Pvp fragment = new Pvp();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
String buttonID = "button_" + i + j;
int resID = getActivity().getResources().getIdentifier(buttonID, "id", getActivity().getPackageName());
buttons[i][j] = getActivity().findViewById(resID);
buttons[i][j].setOnClickListener(this);
}
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.map3x3, container, false);
return view;
}
This is the error message I get
2019-10-25 00:29:31.898 23036-23036/? E/ample.tictacto: Unknown bits set in runtime_flags: 0x8000
2019-10-25 00:29:32.991 23036-23069/com.example.tictactoe E/eglCodecCommon: glUtilsParamSize: unknow param 0x000082da
2019-10-25 00:29:32.991 23036-23069/com.example.tictactoe E/eglCodecCommon: glUtilsParamSize: unknow param 0x000082da
2019-10-25 00:29:38.063 23036-23036/com.example.tictactoe E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.tictactoe, PID: 23036
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.example.tictactoe.Pvp.onCreate(Pvp.java:61)
at androidx.fragment.app.Fragment.performCreate(Fragment.java:2414)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManager.java:1418)
at androidx.fragment.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1195)
at androidx.fragment.app.FragmentTransition.calculateFragments(FragmentTransition.java:1078)
at androidx.fragment.app.FragmentTransition.startTransitions(FragmentTransition.java:117)
at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2408)
at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2366)
at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2273)
at androidx.fragment.app.FragmentManagerImpl$1.run(FragmentManager.java:733)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
