Firebase で Android の定期購入 (Google Billing Library) その３

• Firebase で Android の定期購入 (Google Billing Library) その１
• Firebase で Android の定期購入 (Google Billing Library) その２

準備

    match /purchases {
      allow read, write: if request.auth.uid != null;
      match /{allChildren=**} {
        allow read, write: if request.auth.uid != null;
      }
    }

サーバサイド Functions

firebase functions:config:set env.client_email="purchases@xxx.iam.gserviceaccount.com"
firebase functions:config:set env.private_key="MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwgg..."

import * as functions from "firebase-functions";
import {google} from "googleapis";
import admin = require("firebase-admin");
admin.initializeApp(functions.config().firebase);
const db = admin.firestore();

interface StringKeyObject {
    [key: string]: any;
}

enum SubscriptionNotificationTypes {
    // 定期購入がアカウントの一時停止から復帰した。
    SUBSCRIPTION_RECOVERED = 1,

     // アクティブな定期購入が更新された。
    SUBSCRIPTION_RENEWED = 2,

    // 定期購入が自発的または非自発的にキャンセルされた。
    // 自発的なキャンセルの場合、ユーザーがキャンセルしたときに送信されます。
    SUBSCRIPTION_CANCELED = 3,

    // 新しい定期購入が購入された。
    SUBSCRIPTION_PURCHASED = 4,

    // 定期購入でアカウントが一時停止された（有効な場合）。
    SUBSCRIPTION_ON_HOLD = 5,

    // 定期購入が猶予期間に入った（有効な場合）。
    SUBSCRIPTION_IN_GRACE_PERIOD = 6,

    // ユーザーが [Play] > [アカウント] > [定期購入] から
    // 定期購入を再有効化した（定期購入の再開にはオプトインが必要）。
    SUBSCRIPTION_RESTARTED = 7,

    // 定期購入の料金変更がユーザーによって確認された。
    SUBSCRIPTION_PRICE_CHANGE_CONFIRMED = 8,

    // 定期購入の契約期間が延長された。
    SUBSCRIPTION_DEFERRED = 9,

     // 定期購入が一時停止された。
    SUBSCRIPTION_PAUSED = 10,

     // 定期購入の一時停止スケジュールが変更された。
    SUBSCRIPTION_PAUSE_SCHEDULE_CHANGED = 11,

    // 有効期限前にユーザーが定期購入を取り消した。
    SUBSCRIPTION_REVOKED = 12,

     // 定期購入が期限切れになった。
    SUBSCRIPTION_EXPIRED = 13,
}

const authClient = new google.auth.JWT({
  email: functions.config().env.client_email,
  key: getPrivateKey(functions.config().env.private_key),
  scopes: ["https://www.googleapis.com/auth/androidpublisher"],
});

const playDeveloperApiClient = google.androidpublisher({
  version: "v3",
  auth: authClient,
});

const getSubscription = async (
    token: string,
    subscriptionId: string,
    packageName: string) => {
  await authClient.authorize();
  return playDeveloperApiClient.purchases.subscriptions.get({
    packageName,
    subscriptionId,
    token,
  });
};

/**
 * 秘密鍵に変換する
 * @param {string} privateKey - 文字列
 * @return {string} - 秘密鍵の書式
 */
function getPrivateKey(privateKey: string): string {
  const key = chunkSplit(privateKey, 64, "\n");
  const pkey = "-----BEGIN PRIVATE KEY-----\n" +
        key +
        "-----END PRIVATE KEY-----\n";

  return pkey;
}

/**
 * 指定幅で分割してセパレータで結合した文字列に変換する
 * @param {string} str - 変換元の文字列
 * @param {number} len - 分割する文字数
 * @param {string} end - 結合するセパレータ
 * @return {string} - 変換後の文字列
 */
function chunkSplit(str: string, len: number, end: string): string {
  const match = str.match(new RegExp(".{0," + len + "}", "g"));
  if (!match) {
    return "";
  }

  return match.join(end);
}


/**
 * 購入トークンに紐づけられたドキュメントのIDを取得
 * @param {string} purchaseToken - 購入トークン
 * @return {string} - ドキュメントID
 */
async function queryPurchaseDocId(
    purchaseToken: string): Promise<string | null> {
  const snapShot = await db.collection("purchases")
      .where("purchaseToken", "==", purchaseToken)
      .get();

  let docId = null;
  snapShot.forEach((doc) => {
    if (doc.id) {
      docId = doc.id;
    }
  });

  console.log(`return docId: ${docId}`);
  return docId;
}

/**
 * 購入を登録
 * @param {string} packageName - パッケージ名
 * @param {string} subscriptionId - SKU
 * @param {string} purchaseToken - 購入トークン
 * @param {string} userId - ユーザID
 * @param {string} orderId - オーダID
 * @param {number} startTimeMillis - 購入開始時刻
 * @param {number} expiryTimeMillis - 購入開始時刻
 */
async function insertPurchase(
    packageName: string,
    subscriptionId: string,
    purchaseToken: string,
    userId: string,
    orderId: string,
    startTimeMillis: number,
    expiryTimeMillis: number
) {
  console.log("insertPurchase");

  await db.collection("purchases").add({
    purchaseToken: purchaseToken,
    subscriptionId: subscriptionId,
    packageName: packageName,
    notificationType: 4,
    paymentState: 1,
    orderId: orderId,
    autoRenewing: true,
    cancelReason: -1,
    userId: userId,
    valid: true,
    startTime: admin.firestore.Timestamp.fromMillis(Number(startTimeMillis)),
    expiryTime: admin.firestore.Timestamp.fromMillis(Number(expiryTimeMillis)),
  });
}

/**
 * 購入データを更新
 * @param {number} notificationType - 通知タイプ
 * @param {number} purchaseToken - 購入トークン
 * @param {string} subscriptionId - SKU
 * @param {string} packageName - パッケージ名
 */
async function updatePurchase(notificationType: number,
    purchaseToken: string,
    subscriptionId: string,
    packageName: string) {
  console.log(`updatePurchase(${notificationType})`);

  const response = await getSubscription(
      purchaseToken,
      subscriptionId,
      packageName);

  const subscriptions = response.data;

  const paymentState = subscriptions.paymentState || -1;
  const orderId = subscriptions.orderId || "";
  const expiryTime = admin.firestore.Timestamp
      .fromMillis(Number(subscriptions.expiryTimeMillis));
  const cancelReason = subscriptions.cancelReason || -1;
  const autoRenewing = subscriptions.autoRenewing || false;

  const expiresAt = subscriptions.expiryTimeMillis;
  const valid = (Number(expiresAt) >= Date.now());

  const docId = await queryPurchaseDocId(purchaseToken);
  if (docId == null) {
    throw new functions.https.HttpsError("not-found",
        "Purchase data does not exist: " +
      `purchaseToken : ${purchaseToken}`
    );
  }

  await db.collection("purchases").doc(docId).set({
    notificationType: notificationType,
    paymentState: paymentState,
    orderId: orderId,
    expiryTime: expiryTime,
    cancelReason: cancelReason,
    autoRenewing: autoRenewing,
    valid: valid,
  }, {merge: true});
}

/**
 * 購入データを削除する
 * @param {number} purchaseToken - 購入トークン
 */
async function deletePurchase(purchaseToken: string) {
  console.log(`deletePurchase: ${purchaseToken}`);

  const docId = await queryPurchaseDocId(purchaseToken);
  if (docId == null) {
    // 同一人物がキャンセルして期限が切れた時と
    // 再度定期購入した時の2回 SUBSCRIPTION_EXPIRED が飛んでくる
    console.log("Purchase data has already been deleted");
  } else {
    await db.collection("purchases").doc(docId).delete();
  }
}

exports.verifyPurchaseForAndroid = functions.https
    .onCall(async (data, context) => {
      const {packageName, subscriptionId, purchaseToken} = data;
      const userId = context?.auth?.uid || "";

      // token の重複チェック (存在しなければOK)
      const docId = await queryPurchaseDocId(purchaseToken);
      if (docId != null) {
        throw new functions.https.HttpsError("already-exists",
            "Purchase data already exists");
      }

      // token の正当性チェック (最新の購読情報を取得)
      const response = await getSubscription(
          purchaseToken,
          subscriptionId,
          packageName);
      const subscriptions = response.data;

      // 取得に失敗した場合は検証失敗とする
      if (!subscriptions || response.status !== 200) {
        throw new functions.https.HttpsError("invalid-argument",
            "receipt not found");
      }

      // 購入状態が 1 でなければ検証失敗とする
      if (subscriptions.paymentState !== 1) {
        throw new functions.https.HttpsError("failed-precondition",
            `receipt payment state invalid: ${subscriptions.paymentState}`);
      }

      // 有効期限を確認し、期限切れの場合は検証は失敗とする
      if (subscriptions["expiryTimeMillis"]) {
        if (Number(subscriptions.expiryTimeMillis) <= Date.now()) {
          throw new functions.https.HttpsError("deadline-exceeded",
              "subscriptions expired");
        }
      }

      // ここまでの検証がOKなら、購入情報を登録
      await insertPurchase(packageName,
          subscriptionId,
          purchaseToken,
          userId,
          subscriptions.orderId || "",
          Number(subscriptions.startTimeMillis),
          Number(subscriptions.expiryTimeMillis)
      );

      if (subscriptions.linkedPurchaseToken) {
        // linked があったら、そっちは削除
        await deletePurchase(subscriptions.linkedPurchaseToken);
      }

      return {
        message: "Purchase verification successfully.",
      };
    });

exports.billingPubSub = functions.pubsub
    .topic("billing-notification")
    .onPublish(async (message) => {
      const messageBody = message.data ?
            JSON.parse(Buffer.from(message.data, "base64").toString()) :
            null;

      if (messageBody) {
        const {subscriptionNotification, packageName} = messageBody;

        if (subscriptionNotification) {
          const {notificationType, purchaseToken, subscriptionId} =
            subscriptionNotification;

          console.log(`notificationType: ${notificationType}`);

          switch (notificationType) {
            case SubscriptionNotificationTypes.SUBSCRIPTION_RECOVERED:
            case SubscriptionNotificationTypes.SUBSCRIPTION_RESTARTED:
            case SubscriptionNotificationTypes.SUBSCRIPTION_RENEWED: {
              await updatePurchase(notificationType,
                  purchaseToken,
                  subscriptionId,
                  packageName);
              break;
            }
            case SubscriptionNotificationTypes.SUBSCRIPTION_REVOKED:
            case SubscriptionNotificationTypes.SUBSCRIPTION_EXPIRED: {
              await deletePurchase(purchaseToken);
              break;
            }
            case SubscriptionNotificationTypes.SUBSCRIPTION_CANCELED: {
              await updatePurchase(notificationType,
                  purchaseToken,
                  subscriptionId,
                  packageName);
              break;
            }
            case SubscriptionNotificationTypes.SUBSCRIPTION_ON_HOLD: {
              await updatePurchase(notificationType,
                  purchaseToken,
                  subscriptionId,
                  packageName);
              break;
            }
            case SubscriptionNotificationTypes.SUBSCRIPTION_IN_GRACE_PERIOD: {
              await updatePurchase(notificationType,
                  purchaseToken,
                  subscriptionId,
                  packageName);
              break;
            }
            default:
              break;
          }
        }
      }
    });

クライアントサイド Android モジュール

import com.android.billingclient.api.BillingClient
import com.android.billingclient.api.BillingResult

enum class BillingSkuType(@BillingClient.SkuType val skuType: String) {
    /** 定期購読 */
    Subscription(BillingClient.SkuType.SUBS),

    /** 消費不可のアプリ内アイテム */
    InAppNonConsumable(BillingClient.SkuType.INAPP),

    /** 消費可能なアプリ内アイテム */
    InAppConsumable(BillingClient.SkuType.INAPP),
}

enum class BillingItem(val sku: String, val billingSkuType: BillingSkuType) {
    AdFreeSubscription("ad_free.subscription_01", BillingSkuType.Subscription),
    TestAdFreeSubscription("test.ad_free.subscription_01", BillingSkuType.Subscription);

    companion object {
        fun findBySku(sku: String): BillingItem? = values().find { it.sku == sku }
    }

    fun skusList(): List<String> = listOf(sku)

}

sealed class BillingStatus {
    object SetupSuccess : BillingStatus()
    object BillingFlow : BillingStatus()
    object PendingPurchase : BillingStatus()
    object AcknowledgeSuccess : BillingStatus()
    object ServiceDisconnected : BillingStatus()
    object NoPreviousPlanPurchaseHistory : BillingStatus()
    data class Error(val billingResult: BillingResult) : BillingStatus()
}

import com.google.firebase.Timestamp

class Subscription {
    var userId: String = ""
    var subscriptionId: String = ""
    var packageName: String = ""
    var valid: Boolean = false
    var purchaseToken: String = ""
    var paymentState: Int = -1
    var notificationType: Int = 0
    var startTime: Timestamp = Timestamp.now()
    var expiryTime: Timestamp = Timestamp.now()
    var orderId: String = ""
    var autoRenewing: Boolean = false
    var cancelReason: Int = -1
}

import android.app.Activity
import android.app.Application
import android.util.Log
import androidx.lifecycle.*
import com.android.billingclient.api.*
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.firestore.FirebaseFirestore
import com.google.firebase.functions.ktx.functions
import com.google.firebase.ktx.Firebase

class BillingViewModel(val application: Application) : ViewModel(), BillingClientStateListener,
    PurchasesUpdatedListener, AcknowledgePurchaseResponseListener, LifecycleObserver {

    private val _skuDetails = MutableLiveData<SkuDetails>()
    val skuDetails: LiveData<SkuDetails> = _skuDetails

    private val _subscription = MutableLiveData<Subscription>()
    val subscription: LiveData<Subscription> = _subscription

    private val _billingStatus = MutableLiveData<BillingStatus>()
    val billingStatus: LiveData<BillingStatus> = _billingStatus

    private val billingClient = BillingClient.newBuilder(application)
        .enablePendingPurchases()
        .setListener(this)
        .build()

    override fun onPurchasesUpdated(
        billingResult: BillingResult,
        purchases: MutableList<Purchase>?
    ) {
        if (billingResult.responseCode == BillingClient.BillingResponseCode.OK && purchases != null) {
            purchases.forEach {
                acknowledgePurchase(it)
            }
        } else if (billingResult.responseCode == BillingClient.BillingResponseCode.USER_CANCELED) {
            // cancel
        } else {
            // any other error
        }
    }

    override fun onBillingSetupFinished(billingResult: BillingResult) {
        if (billingResult.responseCode == BillingClient.BillingResponseCode.OK)
            _billingStatus.postValue(BillingStatus.SetupSuccess)
        else
            _billingStatus.postValue(BillingStatus.Error(billingResult))
    }

    override fun onBillingServiceDisconnected() = Unit

    override fun onAcknowledgePurchaseResponse(billingResult: BillingResult) {
        if (billingResult.responseCode == BillingClient.BillingResponseCode.OK) {
            _billingStatus.postValue(BillingStatus.AcknowledgeSuccess)
        } else {
            _billingStatus.postValue(BillingStatus.Error(billingResult))
        }
    }

    override fun onCleared() {
        super.onCleared()
        billingClient.endConnection()
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    fun onCreate() {
        startConnection()
    }

    fun purchase(activity: Activity, billingItem: BillingItem) {
        getSkuDetails(billingItem) { skuDetails ->
            val flowParams = BillingFlowParams.newBuilder()
                .setSkuDetails(skuDetails)
                .build()
            _billingStatus.postValue(BillingStatus.BillingFlow)
            billingClient.launchBillingFlow(activity, flowParams)
        }
    }

    private fun startConnection() {
        billingClient.startConnection(this)
    }

    private fun getSkuDetails(
        billingItem: BillingItem,
        onResponse: (skuDetails: SkuDetails) -> Unit
    ) {
        val skuDetailsParams = SkuDetailsParams.newBuilder()
            .setSkusList(billingItem.skusList())
            .setType(billingItem.billingSkuType.skuType)
            .build()
        billingClient.querySkuDetailsAsync(skuDetailsParams) { billingResult: BillingResult, skuDetailList: List<SkuDetails>? ->
            if (billingResult.responseCode == BillingClient.BillingResponseCode.OK &&
                skuDetailList != null &&
                skuDetailList.isNotEmpty()
            ) {
                onResponse(skuDetailList[0])
            } else {
                _billingStatus.postValue(BillingStatus.Error(billingResult))
            }
        }
    }

    private fun acknowledgePurchase(purchase: Purchase) {

        val data = hashMapOf(
            "packageName" to purchase.packageName,
            "subscriptionId" to purchase.skus[0],
            "purchaseToken" to purchase.purchaseToken
        )

        Firebase.functions
            .getHttpsCallable("verifyPurchaseForAndroid")
            .call(data)
            .addOnSuccessListener {
                if (purchase.purchaseState == Purchase.PurchaseState.PURCHASED
                    && purchase.isAcknowledged.not()
                ) {
                    val acknowledgePurchaseParams = AcknowledgePurchaseParams.newBuilder()
                        .setPurchaseToken(purchase.purchaseToken)
                        .build()
                    billingClient.acknowledgePurchase(acknowledgePurchaseParams, this)
                } else if (purchase.purchaseState == Purchase.PurchaseState.PENDING) {
                    _billingStatus.postValue(BillingStatus.PendingPurchase)
                }
            }
            .addOnFailureListener {
                _billingStatus.postValue(
                    BillingStatus.Error(
                        BillingResult.newBuilder().setResponseCode(99).build()
                    )
                )
            }
    }

    fun querySubscription() {
        val user = FirebaseAuth.getInstance().currentUser

        val db = FirebaseFirestore.getInstance()
        db.collection("purchases")
            .whereEqualTo("userId", user?.uid)
            .whereEqualTo("packageName", application.packageName)
            .whereEqualTo("paymentState", 1)
            .whereEqualTo("valid", true)
            .get()
            .addOnSuccessListener {
                for (doc in it) {
                    doc.toObject(Subscription::class.java).apply {
                        _subscription.postValue(this)
                    }
                }
            }
    }

    fun querySkuDetails(billingItem: BillingItem) {
        getSkuDetails(billingItem) { skuDetails ->
            _skuDetails.postValue(skuDetails)
        }
    }
}

class BillingViewModelFactory(val application: Application) : ViewModelProvider.Factory {

    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        return BillingViewModel(application) as T
    }

}

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>

        <variable
            name="billingViewModel"
            type="com.catoocraft.core.ui.BillingViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".SubscriptionsFragment">

        <TextView
            android:id="@+id/title"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="32dp"
            android:layout_marginEnd="24dp"
            android:text=""
            android:textAppearance="@style/TextAppearance.AppCompat.Body1"
            android:textSize="16sp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/description"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="24dp"
            android:layout_marginEnd="24dp"
            android:text=""
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/title" />

        <TextView
            android:id="@+id/price"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="24dp"
            android:layout_marginEnd="24dp"
            android:text=""
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/description" />

        <View
            android:id="@+id/divider"
            android:layout_width="0dp"
            android:layout_height="1dp"
            android:layout_marginStart="8dp"
            android:layout_marginTop="24dp"
            android:layout_marginEnd="8dp"
            android:background="?android:attr/listDivider"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/price" />

        <TextView
            android:id="@+id/orderIdLabel"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="24dp"
            android:layout_marginEnd="24dp"
            android:text="@string/orderId"
            android:textAppearance="@style/TextAppearance.AppCompat.Body1"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/divider" />

        <TextView
            android:id="@+id/orderId"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="4dp"
            android:layout_marginEnd="24dp"
            android:text="@string/noData"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/orderIdLabel" />

        <TextView
            android:id="@+id/expiryTimeLabel"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="16dp"
            android:layout_marginEnd="24dp"
            android:text="@string/expiryTime"
            android:textAppearance="@style/TextAppearance.AppCompat.Body1"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/orderId" />

        <TextView
            android:id="@+id/expiryTime"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="4dp"
            android:layout_marginEnd="24dp"
            android:text="@string/noData"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/expiryTimeLabel" />

        <TextView
            android:id="@+id/autoRenewingLabel"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="16dp"
            android:layout_marginEnd="24dp"
            android:text="@string/autoRenewing"
            android:textAppearance="@style/TextAppearance.AppCompat.Body1"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/expiryTime" />

        <TextView
            android:id="@+id/autoRenewing"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="24dp"
            android:layout_marginTop="4dp"
            android:layout_marginEnd="24dp"
            android:text="@string/noData"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/autoRenewingLabel" />

        <Button
            android:id="@+id/purchase"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/action_purchase"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/autoRenewing" />


    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

import android.content.ActivityNotFoundException
import android.content.Intent
import android.net.Uri
import android.os.Bundle
import android.text.format.DateUtils.*
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.fragment.app.activityViewModels
import java.time.Period

class SubscriptionsFragment : Fragment() {

    private val billingViewModel by activityViewModels<BillingViewModel> {
        BillingViewModelFactory(
            requireActivity().application
        )
    }

    private var purchased = false

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        val binding = FragmentSubscriptionsBinding.inflate(inflater, container, false).also {
            it.lifecycleOwner = this
        }
        binding.purchase.setOnClickListener {
            if (purchased) {
                startPlayActivity()
            } else {
                billingViewModel.purchase(requireActivity(), BillingItem.AdFreeSubscription)
            }
        }
        billingViewModel.skuDetails.observe(viewLifecycleOwner, {
            it?.let { sku ->
                val period = Period.parse(sku.subscriptionPeriod)
                binding.title.text = sku.title
                binding.description.text = sku.description
                val years = resources.getQuantityString(R.plurals.years, period.years, period.years)
                binding.price.text = resources.getString(R.string.xPerY, sku.price, years)
                binding.purchase.isEnabled = true
            }
        })
        billingViewModel.subscription.observe(viewLifecycleOwner, {
            it?.let { subscriptions ->
                binding.orderId.text = subscriptions.orderId
                binding.expiryTime.text =
                    formatDateTime(
                        context, subscriptions.expiryTime.toDate().time,
                        FORMAT_SHOW_YEAR or FORMAT_SHOW_DATE or FORMAT_ABBREV_ALL
                    )
                binding.autoRenewing.text =
                    getString(if (subscriptions.autoRenewing) R.string.yes else R.string.no)
                binding.purchase.text = getString(R.string.action_manage_subscription)
                purchased = true
            }
        })
        billingViewModel.billingStatus.observe(viewLifecycleOwner, { billingStatus ->
            when (billingStatus) {
                BillingStatus.AcknowledgeSuccess -> {
                    billingViewModel.querySubscription()
                }
            }
        })

        binding.purchase.isEnabled = false

        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        billingViewModel.querySkuDetails(BillingItem.AdFreeSubscription)
    }

    private fun startPlayActivity() {
        try {
            val sku = billingViewModel.skuDetails.value?.sku
            val packageName = requireContext().packageName
            startActivity(
                Intent(
                    Intent.ACTION_VIEW,
                    Uri.parse("https://play.google.com/store/account/subscriptions?sku=${sku}&package=${packageName}")
                )
            )
        } catch (e: ActivityNotFoundException) {
            // showToast("Cant open the browser")
            e.printStackTrace()
        }
    }
}

class MainActivity : AppCompatActivity() {

    val billingViewModel: BillingViewModel by viewModels { BillingViewModelFactory(application) }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        lifecycle.addObserver(billingViewModel)
    }
}

最後に

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