realm null object reference

问题

when i start my app with out network and call my data in my database app crash and this is my code

 public void getAllMovies() {
    findData = realm.where(MovieDb.class).findAll();
    movieArrayList = new ArrayList(findData);
    movieMethod();
}

and i make my conflagration in here

public class myApplication extends Application {

@Override
public void onCreate() {
    super.onCreate();
    RealmConfiguration configuration = new RealmConfiguration
            .Builder(this).name("Movie_database.realm").build();
    Realm.setDefaultConfiguration(configuration);}}

and moviedb is my realm object
my app crash in line

    findData = realm.where(MovieDb.class).findAll();

and this is my error

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.massive.movieapp, PID: 4222
              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.massive.movieapp/com.massive.movieapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'io.realm.RealmQuery io.realm.Realm.where(java.lang.Class)' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                  at android.app.ActivityThread.-wrap11(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:148)
                  at android.app.ActivityThread.main(ActivityThread.java:5417)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'io.realm.RealmQuery io.realm.Realm.where(java.lang.Class)' on a null object reference
                  at com.massive.movieapp.FragmentForActivity.getAllMovies(FragmentForActivity.java:143)
                  at com.massive.movieapp.FragmentForActivity.CallNetwork(FragmentForActivity.java:62)
                  at com.massive.movieapp.FragmentForActivity.onCreate(FragmentForActivity.java:55)
                  at android.app.Fragment.performCreate(Fragment.java:2198)
                  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:942)
                  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1148)
                  at android.app.BackStackRecord.run(BackStackRecord.java:793)
                  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1535)
                  at android.app.FragmentController.execPendingActions(FragmentController.java:325)
                  at android.app.Activity.performStart(Activity.java:6252)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                  at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                  at android.os.Looper.loop(Looper.java:148) 
                  at android.app.ActivityThread.main(ActivityThread.java:5417) 
                  at java.lang.reflect.Method.invoke(Native Method

回答1:

The exception happens because your realm variable is null when you call the getAllMovies method.

Remember to call realm = Realm.getDefaultInstance(); previously.

来源：https://stackoverflow.com/questions/40825065/realm-null-object-reference