FirebaseApp 由 ContentProvider 初始化，因此它在 onCreate() 时未初始化叫.

A FirebaseApp is initialized by a ContentProvider so it is not initialized at the time onCreate() is called.

像这样获取您的 FirebaseDatabase:

Get your FirebaseDatabase like this:

public class Utils {
    private static FirebaseDatabase mDatabase;

    public static FirebaseDatabase getDatabase() {
       if (mDatabase == null) {
          mDatabase = FirebaseDatabase.getInstance();
          mDatabase.setPersistenceEnabled(true);
       }
       return mDatabase;
    }

}

然后从您想要的任何活动中调用 Utils.getDatabase().

Then call Utils.getDatabase() from any activity you want.

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