尝试在空对象引用上调用虚方法boolean com.google.android.gms.common.ConnectionResult.isSuccess（）'

我正在尝试使用教程在我的应用程序中集成FireBase Cloud Messaging：

https://www.simplifiedcoding.net/firebase-cloud-messaging-tutorial-android/

当我试图启动应用程序时，我得到一个空指针异常：

这是logcat：

java.lang.NullPointerException: Attempt to invoke virtual method 
'boolean com.google.android.gms.common.ConnectionResult.isSuccess()' on a null object reference
                                                                               at com.google.android.gms.common.internal.zzd$zzi.zzh(Unknown Source)
                                                                               at com.google.android.gms.common.internal.zzd$zzk.zztp(Unknown Source)
                                                                               at com.google.android.gms.common.internal.zzd$zza.zzc(Unknown Source)
                                                                               at com.google.android.gms.common.internal.zzd$zza.zzw(Unknown Source)
                                                                               at com.google.android.gms.common.internal.zzd$zze.zztr(Unknown Source)
                                                                               at com.google.android.gms.common.internal.zzd$zzd.handleMessage(Unknown Source)
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                               at android.os.Looper.loop(Looper.java:145)
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5942)
                                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                                               at java.lang.reflect.Method.invoke(Method.java:372)
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400)
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)

这是我的build.gradle：

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.0.0'
        //FireBase dependency
        classpath 'com.google.gms:google-services:3.0.0'
    }
}
apply plugin: 'android'


dependencies {
    compile fileTree(include: '*.jar', dir: 'libs')
    //FireBase dependency
    compile 'com.google.firebase:firebase-messaging:10.0.1'
}

android {
    compileSdkVersion 20
    buildToolsVersion '23.0.3'
    sourceSets {
        main {
            manifest.srcFile 'AndroidManifest.xml'
            java.srcDirs = ['src']
            resources.srcDirs = ['src']
            aidl.srcDirs = ['src']
            renderscript.srcDirs = ['src']
            res.srcDirs = ['res']
            assets.srcDirs = ['assets']
            jniLibs.srcDirs = ['libs']
        }

        instrumentTest.setRoot('tests')

        // Move the build types to build-types/<type>
        // For instance, build-types/debug/java, build-types/debug/AndroidManifest.xml, ...
        // This moves them out of them default location under src/<type>/... which would
        // conflict with src/ being used by the main source set.
        // Adding new build types or product flavors should be accompanied
        // by a similar customization.
        debug.setRoot('build-types/debug')
        release.setRoot('build-types/release')
    }
    lintOptions {
        abortOnError false
    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_7
        targetCompatibility JavaVersion.VERSION_1_7
    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_7
        targetCompatibility JavaVersion.VERSION_1_7
    }

    productFlavors {
        x86 {
            ndk {
                abiFilter "x86"
            }
        }
        arm {
            ndk {
                abiFilters "armeabi-v7a", "armeabi"
            }
            minSdkVersion 17
        }
    }
    packagingOptions {
        exclude 'META-INF/DEPENDENCIES'
        exclude 'META-INF/NOTICE'
        exclude 'META-INF/LICENSE'
        exclude 'META-INF/license.txt'
        exclude 'META-INF/notice.txt'
    }
    defaultConfig {
        minSdkVersion 17
        applicationId "com.nytshft.evyt"
    }
}
 //FireBase
    apply plugin: 'com.google.gms.google-services'

Note : I don't have an app module in my application. I have a single build.gradle file.

它与build.gradle有关吗？在官方网站上，他们说要在app文件夹中复制json文件 . 不幸的是我的应用程序没有一个这样的文件夹 . 这是ProjectView Screenshot . 他们还说要在app 's build.gradle. Since I dont have any app folder, I did those changes in the project'的build.gradle文件中添加一些依赖项 .

MyFirebaseInstanceIDService.java :

class MyFirebaseInstanceIDService extends FirebaseInstanceIdService {

    private static final String TAG = "MyFirebaseIIDService";
    @Override
    public void onTokenRefresh() {
        // Get updated InstanceID token.
        String refreshedToken = FirebaseInstanceId.getInstance().getToken();
        Log.d(TAG, "Refreshed token: " + refreshedToken);
        sendRegistrationToServer(refreshedToken);
    }

    private void sendRegistrationToServer(String token) {
        // TODO: Implement this method to send token to your app server.
    }

MyFireBaseMessagingService.java

class MyFirebaseMessagingService extends FirebaseMessagingService {

    private static final String TAG = "MyFirebaseMsgService";
    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {

        Log.d(TAG, "From: " + remoteMessage.getFrom());

        // Check if message contains a data payload.
        if (remoteMessage.getData().size() > 0) {
            Log.d(TAG, "Message data payload: " + remoteMessage.getData());
        }

        // Check if message contains a notification payload.
        if (remoteMessage.getNotification() != null) {
            Log.d(TAG, "Message Notification Body: " + remoteMessage.getNotification().getBody());
            //Calling method to generate notification
            //sendNotification(remoteMessage.getNotification().getBody());
        }
        Toast.makeText(getApplicationContext(), "Push notification: " + remoteMessage.getNotification().getBody(), Toast.LENGTH_LONG).show();


    }


    /**
     * Create and show a simple notification containing the received FCM message.
     * This method is only generating push notification.
     * @param messageBody FCM message body received.
     */
    private void sendNotification(String messageBody) {
        Intent intent = new Intent(this, MainActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0 /* Request code */, intent,
                PendingIntent.FLAG_ONE_SHOT);

        Uri defaultSoundUri= RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
        NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
                .setSmallIcon(R.drawable.androidwidget_logo)
                .setContentTitle("FCM Message")
                .setContentText(messageBody)
                .setAutoCancel(true)
                .setSound(defaultSoundUri)
                .setContentIntent(pendingIntent);

        NotificationManager notificationManager =
                (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        notificationManager.notify(0 /* ID of notification */, notificationBuilder.build());
    }