我只是在探索新的Firebase Firestore，它包含一个称为引用的数据类型。我不清楚这是干什么的。

它像外键吗? 它可以用来指向位于其他地方的集合吗? 如果引用是一个实际的引用，我可以使用它查询吗?例如，我是否可以有一个直接指向用户的引用，而不是将userId存储在文本字段中?我可以使用这个用户引用进行查询吗?

{
  "movies": {
    "movie1": {
      "genre": "comedy",
      "name": "As good as it gets",
      "lead": "Jack Nicholson"
    },
    "movie2": {
      "genre": "Horror",
      "name": "The Shining",
      "lead": "Jack Nicholson"
    },
    "movie3": {
      "genre": "comedy",
      "name": "The Mask",
      "lead": "Jim Carrey"
    }
  }
}

我是Firebase的新手。我如何从上面的数据中检索一个结果类型= '喜剧'和领导= '杰克尼克尔森'?

我有什么选择?

我得到了错误

gettingdocuments.com.google.firebase.firestore.FirebaseFirestoreException: PERMISSION_DENIED:缺少或权限不足。

对于下面关于else语句的代码

db.collection("users")
    .get()
    .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
             if (task.isSuccessful()) {
                 for (DocumentSnapshot document : task.getResult()) {
                     s(document.getId() + " => " + document.getData());
                 }
             } else {
                 s("Error getting documents."+ task.getException());
             }
         }
     });

是否可以使用新的Firebase数据库Cloud Firestore来计算一个集合有多少项?

如果是，我该怎么做?

我正在使用Firebase并测试在应用程序处于后台时从服务器发送通知到我的应用程序。通知发送成功，它甚至出现在设备的通知中心，但当通知出现或即使我点击它，我的FCMessagingService中的onmessagerreceived方法永远不会被调用。

当我测试这个，而我的应用程序是在前台，onmessagerreceived方法被调用，一切工作正常。问题发生在应用程序在后台运行时。

这是我有意为之的行为吗，或者我有办法解决这个问题吗?

这是我的FBMessagingService:

import android.util.Log;

import com.google.firebase.messaging.FirebaseMessagingService;
import com.google.firebase.messaging.RemoteMessage;

public class FBMessagingService extends FirebaseMessagingService {

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        Log.i("PVL", "MESSAGE RECEIVED!!");
        if (remoteMessage.getNotification().getBody() != null) {
            Log.i("PVL", "RECEIVED MESSAGE: " + remoteMessage.getNotification().getBody());
        } else {
            Log.i("PVL", "RECEIVED MESSAGE: " + remoteMessage.getData().get("message"));
        }
    }
}

使用Android Studio 3.3 Canary 11和gradle插件版本3.3.0-alpha11。当尝试同步gradle时，它会抛出以下错误

WARNING: API 'variant.getExternalNativeBuildTasks()' is obsolete and has been 
replaced with 'variant.getExternalNativeBuildProviders()'.
It will be removed at the end of 2019.
For more information, see https://d.android.com/r/tools/task-configuration- 
avoidance
Affected Modules: app

单击错误将我引导到gradle文件中的这一行

applicationVariants.all { variant ->
            variant.outputs.all {
                outputFileName = "${variant.name}-${variant.versionName}.apk"
            }
        }

我到底需要改变什么?

项目build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
        mavenCentral() // jcenter() works as well because it pulls from Maven Central
        maven { url "https://maven.google.com" }
        google()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.3.0-alpha11'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
        classpath "io.realm:realm-gradle-plugin:4.1.1"
        classpath 'com.google.gms:google-services:3.2.1'
        classpath 'com.google.firebase:firebase-plugins:1.1.5'
    }
}

allprojects {
    repositories {
        jcenter()
        maven { url "https://maven.google.com" }
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

// Define versions in a single place
ext {
    // Sdk and tools
    minSdkVersion = 21
    targetSdkVersion = 27
    compileSdkVersion = 27
    buildToolsVersion = '27.0.3'

    // App dependencies
    supportLibraryVersion = '27.1.1'
    appCompactLibraryVersion = '27.1.1'
    playServicesVersion = '15.0.1'
    firebaseVersionCore = '16.0.1'
    firebaseVersionPerf = '16.0.0'
    firebaseVersionMessaging = '17.1.0'

    //lottie
    lottieVersion = '2.5.0'
}

应用build.gradle

buildscript {
    repositories {
        maven { url 'https://maven.fabric.io/public' }
    }

    dependencies {
        classpath 'io.fabric.tools:gradle:1.25.4'
    }
    buildscript {
        repositories {
            maven { url "https://maven.google.com" }
            maven { url 'https://maven.fabric.io/public' }
            mavenCentral()

        }

        dependencies {
            // These docs use an open ended version so that our plugin
            // can be updated quickly in response to Android tooling updates

            // We recommend changing it to the latest version from our changelog:
            // https://docs.fabric.io/android/changelog.html#fabric-gradle-plugin
            classpath 'io.fabric.tools:gradle:'
        }
    }
}
apply plugin: 'com.android.application'
apply plugin: 'com.google.firebase.firebase-perf'
repositories {
    maven { url 'https://maven.fabric.io/public' }
}

apply plugin: 'io.fabric'
apply plugin: 'realm-android'

android {

    realm {
        syncEnabled = false
    }

    dexOptions {
        javaMaxHeapSize "4g"
    }

    compileSdkVersion rootProject.ext.compileSdkVersion

    defaultConfig {
        applicationId "example.com"
        minSdkVersion rootProject.ext.minSdkVersion
        multiDexEnabled true
        versionCode mVersionCode
        versionName mVersionName
        vectorDrawables.useSupportLibrary = true

    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

    buildTypes {

        applicationVariants.all { variant ->
            variant.outputs.all {
                outputFileName = "${variant.name}-${variant.versionName}.apk"
            }
        }

        release {
            shrinkResources true
            minifyEnabled true
            useProguard true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'

            lintOptions {
                disable 'MissingTranslation'
            }

            applicationVariants.all { variant ->
                variant.outputs.all {
                    outputFileName = "${variant.name}-${variant.versionName}.apk"
                }
            }

        }
        debug {
            shrinkResources true
            minifyEnabled true
            useProguard true
            debuggable true
            versionNameSuffix '-DEBUG'
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'debug-proguard-rules.pro'

            ext.enableCrashlytics = false
            crunchPngs false

        }
    }

    flavorDimensions "default"

    lintOptions {

        checkReleaseBuilds false

    }

    packagingOptions {
        exclude 'META-INF/DEPENDENCIES.txt'
        exclude 'META-INF/LICENSE.txt'
        exclude 'META-INF/NOTICE.txt'
        exclude 'META-INF/NOTICE'
        exclude 'META-INF/LICENSE'
        exclude 'META-INF/DEPENDENCIES'
        exclude 'META-INF/notice.txt'
        exclude 'META-INF/license.txt'
        exclude 'META-INF/dependencies.txt'
        exclude 'META-INF/LGPL2.1'
    }
    buildToolsVersion '28.0.2'
}

configurations {
    implementation.exclude group: "org.apache.httpcomponents", module: "httpclient"
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')

    implementation "com.android.support:appcompat-v7:$rootProject.appCompactLibraryVersion"
    implementation "com.android.support:support-compat:$rootProject.supportLibraryVersion"
    implementation "com.android.support:mediarouter-v7:$rootProject.supportLibraryVersion"
    implementation "com.android.support:cardview-v7:$rootProject.supportLibraryVersion"
    implementation "com.android.support:design:$rootProject.supportLibraryVersion"


    api 'com.squareup.retrofit2:retrofit:2.4.0'
    api 'com.squareup.okhttp3:okhttp:3.11.0'
    api 'com.squareup.okhttp3:logging-interceptor:3.10.0'
    implementation 'com.google.code.gson:gson:2.8.2'
    implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
    implementation 'com.squareup.picasso:picasso:2.5.2'
    implementation 'com.squareup.retrofit2:adapter-rxjava:2.3.0'
    implementation 'com.android.support:multidex:1.0.3'
    implementation 'com.daimajia.easing:library:2.0@aar'
    implementation 'com.daimajia.androidanimations:library:2.3@aar'

    implementation 'com.akexorcist:googledirectionlibrary:1.0.5'
    implementation 'io.reactivex:rxandroid:1.2.1'
    implementation 'io.reactivex:rxjava:1.3.0'
    // Wifi hotspot library
    implementation 'cc.mvdan.accesspoint:library:0.2.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'org.jsoup:jsoup:1.10.3'
    api "com.airbnb.android:lottie:$rootProject.lottieVersion"
    implementation 'com.android.support:support-v4:27.1.1'
    implementation 'com.android.support:recyclerview-v7:27.1.1'
    testImplementation 'junit:junit:4.12'
    implementation 'com.jakewharton:butterknife:8.8.1'

    debugImplementation 'com.squareup.leakcanary:leakcanary-android:1.5.4'
    releaseImplementation 'com.squareup.leakcanary:leakcanary-android-no-op:1.5.4'

    implementation 'com.googlecode.libphonenumber:libphonenumber:8.2.0'

    implementation "com.google.android.gms:play-services-base:$rootProject.playServicesVersion"
    implementation "com.google.android.gms:play-services-cast-framework:$rootProject.playServicesVersion"
    implementation "com.google.android.gms:play-services-auth:$rootProject.playServicesVersion"
    implementation "com.google.android.gms:play-services-identity:$rootProject.playServicesVersion"
    implementation "com.google.android.gms:play-services-awareness:$rootProject.playServicesVersion"
    implementation "com.google.android.gms:play-services-cast:$rootProject.playServicesVersion"
    implementation "com.google.android.gms:play-services-drive:$rootProject.playServicesVersion"
    implementation "com.google.android.gms:play-services-location:$rootProject.playServicesVersion"
    implementation "com.google.android.gms:play-services-maps:$rootProject.playServicesVersion"

    implementation "com.google.firebase:firebase-core:$rootProject.firebaseVersionCore"
    implementation "com.google.firebase:firebase-perf:$rootProject.firebaseVersionPerf"
    implementation "com.google.firebase:firebase-messaging:$rootProject.firebaseVersionMessaging"
    implementation "com.google.firebase:firebase-analytics:$rootProject.firebaseVersionCore"


    api('com.crashlytics.sdk.android:crashlytics:2.8.0@aar') {
        transitive = true
    }
    api('com.crashlytics.sdk.android:answers:1.4.1@aar') {
        transitive = true
    }
    annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1'
    api project(path: ':libraryBTHelper')
    api project(':bkk_rush')

    debugApi 'com.amitshekhar.android:debug-db:1.0.3'
    api "org.jdeferred:jdeferred-android-aar:1.2.6"
    implementation 'com.android.support:gridlayout-v7:27.1.1'
}

apply plugin: 'com.google.gms.google-services'

我已经跳过了app/build中的一些常量和其他敏感信息。gradle文件。

我正试着理清思路。我喜欢可观察对象解决开发和可读性问题的方式。正如我读到的，好处是巨大的。

HTTP和集合上的可观察对象似乎很直接。我怎么把这样的东西转换成可观察的模式。

这来自我的服务组件，用于提供身份验证。我希望它能像Angular2中的其他HTTP服务一样工作——支持数据、错误和完成处理程序。

firebase.auth().createUserWithEmailAndPassword(email, password)
  .then(function(firebaseUser) {
    // do something to update your UI component
    // pass user object to UI component
  })
  .catch(function(error) {
    // Handle Errors here.
    var errorCode = error.code;
    var errorMessage = error.message;
    // ...
  });

如果有任何帮助，我将不胜感激。我拥有的唯一替代解决方案是创建eventemitter。但我想在服务部门这样做是很糟糕的

谷歌刚刚发布了Cloud Firestore，这是他们针对应用程序的新文档数据库。

我一直在阅读文档，但我没有看到Firestore和Firebase DB之间有太多区别。

主要的一点是，Firestore使用文档和集合，与Firebase相比，它可以轻松使用查询，Firebase是一个传统的带有JSON基的noSQL数据库。

我想知道更多关于它们的区别或用法，或者Firestore是否只是来取代Firebase DB?

我正在构建一个Flutter应用程序，我已经集成了Firebase，但当我点击一个按钮注册，登录或注销时，我一直得到这个错误。我看到其他人也问过同样的问题，但似乎没有一个对我有用。我正在使用Flutter和Android Studio。我该如何解决这个问题?

这是我的代码的摘录

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.red,
      body: Center(
        child: Container(
          child: RaisedButton(
            onPressed: () {
              FirebaseAuth.instance.signOut().then((value) {
                Navigator.pushReplacement(
                    context,
                    MaterialPageRoute(
                        builder: (context) =>
                            LoginScreen()));
              });
            },
            child: Text("Logout"),
          )
        )
      )
    );
  }
}

下面是抛出的异常

══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
The following FirebaseException was thrown while handling a gesture:
[core/no-app] No Firebase App '[DEFAULT]' has been created - call Firebase.initializeApp()

When the exception was thrown, this was the stack:

#0      MethodChannelFirebase.app (package:firebase_core_platform_interface/src/method_channel/method_channel_firebase.dart:118:5)
#1      Firebase.app (package:firebase_core/src/firebase.dart:52:41)
#2      FirebaseAuth.instance (package:firebase_auth/src/firebase_auth.dart:37:47)
#3      _HomeScreenState.build.<anonymous closure> (package:cosytok/screens/home.dart:20:28)
#4      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:992:19)
#5      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:1098:38)
#6      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:184:24)
#7      TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:524:11)
#8      BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:284:5)
#9      BaseTapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:219:7)
#10     PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:477:9)
#11     PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:78:12)
#12     PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:124:9)
#13     _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:377:8)
#14     PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:122:18)
#15     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:108:7)
#16     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:220:19)
#17     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:200:22)
#18     GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:158:7)
#19     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:104:7)
#20     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:88:7)
#24     _invoke1 (dart:ui/hooks.dart:267:10)
#25     _dispatchPointerDataPacket (dart:ui/hooks.dart:176:5)
(elided 3 frames from dart:async)

Handler: "onTap"
Recognizer:
  TapGestureRecognizer#f0104
════════════════════════════════════════════════════════════════════════════════════════════════════

════════ Exception caught by gesture ═══════════════════════════════════════════════════════════════
The following FirebaseException was thrown while handling a gesture:
[core/no-app] No Firebase App '[DEFAULT]' has been created - call Firebase.initializeApp()

这是我的舱单:

<service android:name=".fcm.PshycoFirebaseMessagingServices">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT" />
    </intent-filter>
</service>

<service android:name=".fcm.PshycoFirebaseInstanceIDService">
    <intent-filter>
        <action android:name="com.google.firebase.INSTANCE_ID_EVENT" />
    </intent-filter>
</service>

当应用程序在后台和通知到达，然后默认通知来，不运行我的onmessagerreceived代码。

这是我的onMessageReceived代码。如果我的应用程序在前台运行，而不是在后台运行，就会调用这个函数。我怎么能运行这段代码时，应用程序是在后台太?

// [START receive_message]
@Override
public void onMessageReceived(RemoteMessage remoteMessage) {
    // TODO(developer): Handle FCM messages here.
    // If the application is in the foreground handle both data and notification messages here.
    // Also if you intend on generating your own notifications as a result of a received FCM
    // message, here is where that should be initiated. See sendNotification method below.
    data = remoteMessage.getData();
    String title = remoteMessage.getNotification().getTitle();
    String message = remoteMessage.getNotification().getBody();
    String imageUrl = (String) data.get("image");
    String action = (String) data.get("action");
    Log.i(TAG, "onMessageReceived: title : "+title);
    Log.i(TAG, "onMessageReceived: message : "+message);
    Log.i(TAG, "onMessageReceived: imageUrl : "+imageUrl);
    Log.i(TAG, "onMessageReceived: action : "+action);

    if (imageUrl == null) {
        sendNotification(title,message,action);
    } else {
        new BigPictureNotification(this,title,message,imageUrl,action);
    }
}
// [END receive_message]