android - 确保首先在 Android 中调用 FirebaseApp.initializeApp(Context)

Question

我正面临这个问题，并在这个网站上看到了一些答案，但没有得到任何适当的解决方案。
我使用了以前版本的 Firebase 工作正常，但是当我尝试使用 Upgradation 进行升级时并将 Firebase 类更新为 DatabaseReference 它显示错误并且无法正常工作。
我正在添加我的 list 文件的整个代码，所以请帮我解决这个问题。
这是我的 manifest

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="firebasechat.com.firebasechat">

    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:name=".Activity.SimpleBlog"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".Activity.RegisterActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>

</manifest>

我的Module app如下。

    apply plugin: 'com.android.application'

android {
    compileSdkVersion 26
    buildToolsVersion "26.0.0"
    defaultConfig {
        applicationId "firebasechat.com.firebasechat"
        minSdkVersion 15
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

        multiDexEnabled  true

    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    packagingOptions {
        exclude 'META-INF/LICENSE'
        exclude 'META-INF/LICENSE-FIREBASE.txt'
        exclude 'META-INF/NOTICE'
    }
}



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-v7:26.+'
compile 'com.android.volley:volley:1.0.0'
compile "com.google.firebase:firebase-database:11.0.0"
compile 'com.google.android.gms:play-services:11.0.0'
compile 'com.android.support:recyclerview-v7:25.0.0'
testCompile 'junit:junit:4.12'
    testCompile 'junit:junit:4.12'
}

和项目等级

    // 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:4.2.0'// Updated version of google service
    }
}
allprojects {
    repositories {
        jcenter()
        maven {
            url "https://maven.google.com" // Google's Maven repository
        }
    }
}
task clean(type: Delete) {
    delete rootProject.buildDir
}

下面是我的Activity。

    public class RegisterActivity extends AppCompatActivity {

    EditText username, password;
    Button registerButton;
    String user, pass;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);

        username = (EditText)findViewById(R.id.username);
        password = (EditText)findViewById(R.id.password);
        registerButton = (Button)findViewById(R.id.registerButton);


          FirebaseApp.initializeApp(this);



        registerButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                user = username.getText().toString();
                pass = password.getText().toString();


                    final ProgressDialog pd = new ProgressDialog(RegisterActivity.this);
                    pd.setMessage("Loading...");
                    pd.show();

                    String url = "https://pure-coda-174710.firebaseio.com/users.json";

                    StringRequest request = new StringRequest(Request.Method.GET, url, new Response.Listener<String>(){
                        @Override
                        public void onResponse(String s) {

//                            Firebase reference = new Firebase("https://pure-coda-174710.firebaseio.com/users");
                            DatabaseReference reference = FirebaseDatabase.getInstance()
                                    .getReferenceFromUrl("https://pure-coda-174710.firebaseio.com/users");


                            if(s.equals("null")) {
                                reference.child(user).child("password").setValue(pass);
                                Toast.makeText(RegisterActivity.this, "registration successful", Toast.LENGTH_LONG).show();
                            }
                            else {
                                try {
                                    JSONObject obj = new JSONObject(s);

                                    if (!obj.has(user)) {
                                        reference.child(user).child("password").setValue(pass);
                                        Toast.makeText(RegisterActivity.this, "registration successful", Toast.LENGTH_LONG).show();
                                    } else {
                                        Toast.makeText(RegisterActivity.this, "username already exists", Toast.LENGTH_LONG).show();
                                    }

                                } catch (JSONException e) {
                                    e.printStackTrace();
                                }
                            }

                            pd.dismiss();
                        }

                    },new Response.ErrorListener(){
                        @Override
                        public void onErrorResponse(VolleyError volleyError) {
                            System.out.println("" + volleyError );
                            pd.dismiss();
                        }
                    });

                    RequestQueue rQueue = Volley.newRequestQueue(RegisterActivity.this);
                    rQueue.add(request);

            }
        });
    }
}

Answer 1

在您的 SimpleBlog 应用程序类中，在 onCreate() 方法中初始化 FirebaseApp 并将其从 RegisterActivity 中移除，以便让 Firebase 初始化为 < strong>整个应用程序，而不仅仅是一个 Activity。

@Override
public void onCreate() {
    super.onCreate();
    FirebaseApp.initializeApp(this);
}

另外在 app gradle 末尾添加 apply plugin: 'com.google.gms.google-services':

dependencies {
    ....
}

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

需要插件来处理来自 firebase 的 json 配置并避免依赖冲突。您可以阅读here了解更多详情。