Change TextView when Navigation Drawer Item is selected

Question

I'm trying to make three different options in my navigation drawer use the same fragment but with different values in the TextView in that fragment.

I created a standard Navigation Drawer Activity with Android Studio and tried to use setText in the same method that changes the title, see below:

public void onSectionAttached(int number) {
        switch (number) {
            case 1:
                mTitle = getString(R.string.title_section1);
                Namn.setText("Item 1");
                break;
            case 2:
                mTitle = getString(R.string.title_section2);
                Namn.setText("Item 2");
                break;
            case 3:
                mTitle = getString(R.string.title_section3);
                Namn.setText("Item 3");
                break;
        }
    }

When I try to run the app it force closes instantly and I get this error:

Process: com.test.je.test, PID: 22605
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.test.je.test/com.test.je.test.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2187)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2236)
            at android.app.ActivityThread.access$800(ActivityThread.java:138)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1199)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5034)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:611)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.test.je.test.MainActivity.onSectionAttached(MainActivity.java:68)
            at com.test.je.test.MainActivity$PlaceholderFragment.onAttach(MainActivity.java:153)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:903)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
            at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:548)
            at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
            at android.app.Activity.performStart(Activity.java:5251)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2160)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2236)
            at android.app.ActivityThread.access$800(ActivityThread.java:138)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1199)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5034)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:611)
            at dalvik.system.NativeStart.main(Native Method)

I have declared the TextView with TextView Namn; and Namn = (TextView)findViewById(R.id.twnamn);

What am I doing wrong here?

Answer 1

So user @feresr helped me understand what was wrong with his comment.

I created an if statement in the onCreateView() method instead and it solved the problem.

I had to declare the textview after the fragment had been created also.

Here is the code:

public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView;
            Bundle args = getArguments();
            int currentView = getArguments().getInt(ARG_SECTION_NUMBER);

            if(currentView == 1){
                rootView = inflater.inflate(R.layout.fragment_main, container, false);
                TextView Namn = (TextView) rootView.findViewById(R.id.twnamn);
                Namn.setText("Val 1");
            }else if(currentView == 2){
                rootView = inflater.inflate(R.layout.fragment_main, container, false);
                TextView Namn = (TextView) rootView.findViewById(R.id.twnamn);
                Namn.setText("Val 2");
            }else if(currentView == 3){
                rootView = inflater.inflate(R.layout.fragment_main, container, false);
                TextView Namn = (TextView) rootView.findViewById(R.id.twnamn);
                Namn.setText("Val 3");
            }else {
                rootView = inflater.inflate(R.layout.fragment_main, container, false);
            }


            return rootView;
        }