Singleton-Methode gibt Fehler in OnResum (Android)

Question

Ich habe ein Problem, dass ich nicht verstehen konnte, warum es passiert.

Ich habe ein Fragment, und in dem Fragment Ich habe das bei der Wiederaufnahme Methode wie folgt:

@Override 
public void onResume(){ 
    super.onResume(); 

    System.out.println("number 1"); 

    int s = ((StarterApplication) this.getActivity().getApplication()).getRefreshNotificationVar(); 

    System.out.println("number 2"); 
    s = s + 1; 

    System.out.println("number 3"); 
    ((StarterApplication) this.getActivity().getApplication()).setRefreshNotificationVar(s); 

    System.out.println("number 4"); 
    System.out.println(s); 


} 

Und meine Singletons sind wie folgt:

private int refreshNotificationVar; 

public int getRefreshNotificationVar() { 

    System.out.println("check out here"); 
    return refreshNotificationVar; 
} 

public void setRefreshNotificationVar(int refreshNotificationVar) { 
    this.refreshNotificationVar = refreshNotificationVar; 
    System.out.println(refreshNotificationVar+" is my number"); 

} 

Und ich nenne das Fragment einmal in das Erstellen der Aktivität wie unten, was gut funktioniert. Die Singleton-Methoden und sonst.

newsFeedFragment fragment2 = new newsFeedFragment(); 
android.support.v4.app.FragmentTransaction fragmentTransaction2 = getSupportFragmentManager().beginTransaction(); 
fragmentTransaction2.add(R.id.fragment_container, fragment2, "news_feed_fragment"); 
fragmentTransaction2.addToBackStack(null); 
fragmentTransaction2.commit(); 

Und ich nenne dieses Fragment wieder mit einer Schaltfläche wie folgt. Allerdings beginne ich hier den Fehler zu bekommen, wenn die Singleton-Methode startet.

newsFeedFragment fragment = new newsFeedFragment(); 
android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction(); 
fragmentTransaction.hide(getSupportFragmentManager().findFragmentById(R.id.fragment_container)); 
fragmentTransaction.hide(getSupportFragmentManager().findFragmentByTag("notifications_fragment")); 
fragmentTransaction.show(getSupportFragmentManager().findFragmentByTag("news_feed_fragment")); 
fragmentTransaction.addToBackStack(null); 
fragmentTransaction.commit(); 
fragment.onResume(); 

Wenn das Fragment lädt zum ersten Mal, es funktioniert gut, aber wenn ich manuell das Fragment und starten Sie die onResume Methode zeigen, beginne ich, wie unten um den Fehler zu erhalten:

E/AndroidRuntime: FATAL EXCEPTION: main 
java.lang.IllegalStateException: Could not execute method for android:onClick 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293) 
    at android.view.View.performClick(View.java:3511) 
    at android.view.View$PerformClick.run(View.java:14105) 
    at android.os.Handler.handleCallback(Handler.java:605) 
    at android.os.Handler.dispatchMessage(Handler.java:92) 
    at android.os.Looper.loop(Looper.java:137) 
    at android.app.ActivityThread.main(ActivityThread.java:4424) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:511) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
    at dalvik.system.NativeStart.main(Native Method) 
Caused by: java.lang.reflect.InvocationTargetException 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:511) 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
    at android.view.View.performClick(View.java:3511) 
    at android.view.View$PerformClick.run(View.java:14105) 
    at android.os.Handler.handleCallback(Handler.java:605) 
    at android.os.Handler.dispatchMessage(Handler.java:92) 
    at android.os.Looper.loop(Looper.java:137) 
    at android.app.ActivityThread.main(ActivityThread.java:4424) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:511) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
    at dalvik.system.NativeStart.main(Native Method) 
Caused by: java.lang.NullPointerException 
    at com.my_last.mylast.newsFeedFragment.onResume(newsFeedFragment.java:223) 
    at com.my_last.mylast.MainActivity.go_to_main_view(MainActivity.java:565) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:511) 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
    at android.view.View.performClick(View.java:3511) 
    at android.view.View$PerformClick.run(View.java:14105) 
    at android.os.Handler.handleCallback(Handler.java:605) 
    at android.os.Handler.dispatchMessage(Handler.java:92) 
    at android.os.Looper.loop(Looper.java:137) 
    at android.app.ActivityThread.main(ActivityThread.java:4424) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:511) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
    at dalvik.system.NativeStart.main(Native Method) 

Does Hat jemand eine Ahnung davon?

Answer 1

@Override 
    public void onActivityCreated(@Nullable Bundle savedInstanceState) { 
     super.onActivityCreated(savedInstanceState); 
     System.out.println("number 1"); 
     int s = ((MainApplication) this.getActivity().getApplication()).getRefreshNotificationVar(); 
     System.out.println("number 2"); 
     s = s + 1; 
     System.out.println("number 3"); 
     ((MainApplication) this.getActivity().getApplication()).setRefreshNotificationVar(s); 
     System.out.println("number 4"); 
     System.out.println(s); 
    } 

Sieht aus wie Aktivitätsinstanz ist null. Anstatt onresume die gleiche Operation auf OnActivityCreated-Methode. Bitte beachten Sie den obigen Code.