I'm making app that has 3 fragment and 1 activity.
And I want
if Button at fragment named 'FragmentOper" is clicked,
two buttons in Activity named 'FragmentMain' is disabled.
I have been searched on the internet and found i simple way.
FragmentMain.java
public class FragmentMain extends AppCompatActivity {
public static Button BtnInit, btnOper, btnGraph;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
btnInit = (Button) findViewById(R.id.button1);
btnOper = (Button) findViewById(R.id.button2);
btnGraph = (Button) findViewById(R.id.button3);
setContentView(R.layout.activity_fragment); // added
FragmentMain.context = FragmentMain.this; // added
}
// added to stack Overflow codes
public void changeFragment(View view){
int id = view.getId();
Fragment fragment = null;
switch (id){
case R.id.button1:
fragment = new FragmentInit();
break;
case R.id.button2:
fragment = new FragmentOper();
break;
case R.id.button3:
fragment = new FragmentGraph();
break;
}
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.fragment, fragment);
fragmentTransaction.commit();
}
public void changeState(boolean state){
FragmentMain.btnGraph.setEnabled(state);
FragmentMain.btnInit.setEnabled(state);
}
}
FragmentOper.java
public class FragmentOper extends Fragment{
public Button mStartBtn;
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
@Nullable Bundle savedInstanceState) {
View myView = inflater.inflate(R.layout.fragment_oper, container, false);
mStartBtn = (Button) myView.findViewById(R.id.startBtn);
mStartBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View myView) {
if (isTimerRunning) // STOP
{
mStartBtn.setText("START");
isTimerRunning = false;
timerHandler.removeCallbacks(timerRunnable);
((FragmentMain)getActivity()).changeState(true);
} else {
mStartBtn.setText("PAUSE"); // Working
startTimer();
((FragmentMain)getActivity()).changeState(false);
}
}
});
return myView;
}
But There is java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setEnabled(boolean)' on a null object reference error in changeState in 'FragmentMain'
When this app is started, I pressed btnINIT and btnGRAPH and it is worked.
And before I add ((FragmentMain)getActivity()).changeState(true); in onclicklistener, it works fine.
So i don't understand why there is an NullPointerException.
I have never declared Buttons in any other place.
How can it fixed?
