选择导航抽屉项时更改TextView

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;
        }