确保首先调用FirebaseApp.initializeApp（Context）

Question

其他问题可能已经完全相同，但是我真的不知道这里有什么问题。在此先感谢您的帮助。

build.gradle（项目）

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

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.3'
        classpath 'com.google.gms:google-services:3.1.0'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
        maven {
            url "https://maven.google.com" // Google's Maven repository
        }
    }
}

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

build.gradle（模块）

    apply plugin: 'com.android.application'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.3"
    defaultConfig {
        applicationId "com.bustracker.usc.myapplication"
        minSdkVersion 21
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.3.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha7'
    compile 'com.google.android.gms:play-services-maps:10.2.6'
    compile 'com.google.android.gms:play-services-location:10.2.6'
    compile 'com.google.firebase:firebase-database:10.2.6'
    testCompile 'junit:junit:4.12'
}

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

MainActivity.java

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        FirebaseApp.initializeApp(this);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        firebaseDatabase = FirebaseDatabase.getInstance();
        mRootReference = firebaseDatabase.getReference();
        mheadingReference = mRootReference.child("users");

错误：

FATAL EXCEPTION: main
                                                 Process: com.bustracker.sample.myapplication, PID: 2658
                                                 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bustracker.sample.myapplication/com.bustracker.sample.myapplication.MainActivity}: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.bustracker.sample.myapplication. Make sure to call FirebaseApp.initializeApp(Context) first.
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                     at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                     at android.os.Handler.dispatchMessage(Handler.java:102)
                                                     at android.os.Looper.loop(Looper.java:154)
                                                     at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                  Caused by: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.bustracker.sample.myapplication. Make sure to call FirebaseApp.initializeApp(Context) first.
                                                     at com.google.firebase.FirebaseApp.getInstance(Unknown Source)
                                                     at com.google.firebase.database.FirebaseDatabase.getInstance(Unknown Source)
                                                     at com.bustracker.sample.myapplication.MainActivity.onCreate(MainActivity.java:53)
                                                     at android.app.Activity.performCreate(Activity.java:6679)
                                                     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
                                                     at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
                                                     at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                     at android.os.Looper.loop(Looper.java:154) 
                                                     at android.app.ActivityThread.main(ActivityThread.java:6119) 
                                                     at java.lang.reflect.Method.invoke(Native Method) 
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

其他问题可能已经完全相同，但是我真的不知道这里有什么问题。在此先感谢您的帮助。

Answer 1

根据文档：

如文档中所述：

任何FirebaseApp初始化必须仅在应用程序的主要过程中发生。不支持在主流程以外的其他流程中使用Firebase，这可能会导致与资源争用相关的问题。

您无需在活动中初始化它。

将应用程序类添加到清单示例中：

      <applicaton
       android:name="MyApplication"

然后这样做：

public class MyApplication extends Application {
  @Override
public void onCreate() {
    super.onCreate();
   FirebaseApp.initializeApp(this);
}

并从活动中删除初始化。您需要在作为基类的应用程序类中对其进行初始化。

编辑（关于应用程序）：

用于维护全局应用程序状态的基类。您可以通过创建一个子类并在AndroidManifest.xml的标签中将该子类的标准名称指定为“
android：name”属性来提供自己的实现。创建应用程序/包的过程时，将在任何其他类之前实例化Application类或Application类的子类。

有用的链接：https
:
//developer.android.com/reference/android/app/Application.html