所以我只是尝试使用Firebase从实时数据库更新活动的工具栏标签。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)
即使我在调用数据库实例上的任何其他方法之前使用setPersistenceEnabled（），我仍然会收到此错误。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) {
}
});
// ---------------------------------------------------------------------------
导致崩溃的原因。我在其他两项活动中使用完全相同的代码段...
答案 0 :(得分：4)
此部分mFirebaseInstance.setPersistenceEnabled(true);应该只在第一个Activity中。不应该多次调用它。
更好的解决方案是将该行放在Application类的onCreate方法中。您可以阅读更多相关信息here。
答案 1 :(得分：0)
从mFirebaseInstance.setPersistenceEnabled(true);课程中删除RegisterActivity行。
创建一个自定义类，它应该扩展Application并将其写在那里。
示例：
public class JustExample extends Application {
@Override
public void onCreate() {
super.onCreate();
if (!FirebaseApp.getApps(this).isEmpty())
{
FirebaseDatabase.getInstance().setPersistenceEnabled(true);
}
}
}
答案 2 :(得分：0)
boolean flag = true; //before onCreate() method
//inside onStart() Method
if(flag)
{
firebaseDatabase.setPersistenceEnabled(true);
flag = false;
}
答案 3 :(得分：0)
您可以使用Model类并在其中使用Method，如下所述。
public class DatabaseUtility {
private static FirebaseDatabase database;
public static FirebaseDatabase getDatabase(){
if(database==null){
database=FirebaseDatabase.getInstance();
database.setPersistenceEnabled(true);
}
return database;
}
}
这将返回数据库实例，您可以使用database.getReference();方法获取Root引用。如果数据库对象已存在，这也将节省一些时间。
答案 4 :(得分：0)
您只需卸载以前安装的应用即可。并让它安装新的应用程序。它将解决问题。