Android Firebase - setPersistenceEnabled(true) 使应用程序崩溃

Question

所以我只是尝试使用 Firebase 来更新实时数据库中活动的工具栏标签。我收到以下错误：

12-21 00:25:19.890 10295-10295/com.xlr8labs.FirebaseAuth E/AndroidRuntime: FATAL EXCEPTION: main
                                                                       Process: com.xlr8labs.FirebaseAuth, PID: 10295
                                                                       java.lang.RuntimeException: Unable to start activity ComponentInfo{com.xlr8labs.FirebaseAuth/com.xlr8labs.FirebaseAuth.RegisterActivity}: com.google.firebase.database.DatabaseException: Calls to setPersistenceEnabled() must be made before any other usage of FirebaseDatabase instance.
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2341)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2393)
                                                                           at android.app.ActivityThread.access$800(ActivityThread.java:151)
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1324)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:110)
                                                                           at android.os.Looper.loop(Looper.java:193)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5295)
                                                                           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:828)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:644)
                                                                           at dalvik.system.NativeStart.main(Native Method)
                                                                        Caused by: com.google.firebase.database.DatabaseException: Calls to setPersistenceEnabled() must be made before any other usage of FirebaseDatabase instance.
                                                                           at com.google.firebase.database.FirebaseDatabase.zzhM(Unknown Source)
                                                                           at com.google.firebase.database.FirebaseDatabase.setPersistenceEnabled(Unknown Source)
                                                                           at com.xlr8labs.FirebaseAuth.RegisterActivity.onCreate(RegisterActivity.java:35)
                                                                           at android.app.Activity.performCreate(Activity.java:5264)
                                                                           at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2393) 
                                                                           at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1324) 
                                                                           at android.os.Handler.dispatchMessage(Handler.java:110) 
                                                                           at android.os.Looper.loop(Looper.java:193) 
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5295) 
                                                                           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:828) 
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:644) 
                                                                           at dalvik.system.NativeStart.main(Native Method) 

即使我在我的数据库实例上调用任何其他方法之前使用 setPersistenceEnabled()，我仍然收到此错误。这是我的 Activity.java 代码：

public class RegisterActivity extends AppCompatActivity {
 private FirebaseDatabase mFirebaseInstance;
 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);
        // ------------------ Update activity label from database in realtime ------
        mFirebaseInstance = FirebaseDatabase.getInstance();
        mFirebaseInstance.setPersistenceEnabled(true);
        mFirebaseInstance.getReference("RegisterLabel").keepSynced(true);
        mFirebaseInstance.getReference("RegisterLabel").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                Log.e(LOG_TAG,"Register label changed");
                String appTitle = dataSnapshot.getValue().toString();
                getSupportActionBar().setTitle(appTitle);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
        // ---------------------------------------------------------------------------

是什么导致崩溃。我在另外两个活动中使用完全相同的代码片段......

Answer 1

这部分mFirebaseInstance.setPersistenceEnabled(true);应该只是在第一个活动中。它不应被多次调用。

更好的解决方案是将该行放在 Application 类的 onCreate 方法中。您可以在此处阅读更多相关信息。