Android in-app purchase billing client crashes on build

Question

I am new to Android in-app purchases. I have followed the official documentation and I can't go beyond building the BillingClient as app crashes when it tries to build the BillingClient. Any help or any reference to a android in-app purchases in Java is much appreciated. My MainActivity.java codes is as follows:

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.webkit.WebSettings;
import android.webkit.WebView;

import com.android.billingclient.api.BillingClient;
import com.android.billingclient.api.BillingClientStateListener;
import com.android.billingclient.api.BillingResult;
import com.android.billingclient.api.Purchase;
import com.android.billingclient.api.PurchasesUpdatedListener;
import java.util.List;

public class MainActivity extends AppCompatActivity{

    private PurchasesUpdatedListener purchaseUpdateListener = new PurchasesUpdatedListener() {
        @Override
        public void onPurchasesUpdated(BillingResult billingResult, List<Purchase> purchases) {
            // To be implemented in a later section.
        }
    };


    private BillingClient billingClient = BillingClient.newBuilder(MainActivity.this)
            .setListener(purchaseUpdateListener)
            .enablePendingPurchases()
            .build();


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

}

Crash Log is as follows:

2020-07-07 01:19:40.667 27956-27956/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.js.bs, PID: 27956
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.js.bs/com.js.bs.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3272)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3500)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2049)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7523)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:941)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
        at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:122)
        at com.android.billingclient.api.BillingClientImpl.initialize(com.android.billingclient:billing@@3.0.0:26)
        at com.android.billingclient.api.BillingClientImpl.<init>(com.android.billingclient:billing@@3.0.0:13)
        at com.android.billingclient.api.BillingClientImpl.<init>(com.android.billingclient:billing@@3.0.0:1)
        at com.android.billingclient.api.BillingClient$Builder.build(com.android.billingclient:billing@@3.0.0:14)
        at com.js.bs.MainActivity.<init>(MainActivity.java:31)
        at java.lang.Class.newInstance(Native Method)
        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
        at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:41)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1253)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3260)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3500) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2049) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:223) 
        at android.app.ActivityThread.main(ActivityThread.java:7523) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:941) 
2020-07-07 01:19:41.044 27956-27956/? I/Process: Sending signal. PID: 27956 SIG: 9

Answer 1

Please change the billingClient object creation as below. While creating this object from outside the context may be null, so crashing. Move the object creation to onCreate() method of the activity.

    private BillingClient billingClient;

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

        billingClient = BillingClient.newBuilder(this)
            .setListener(purchaseUpdateListener)
            .enablePendingPurchases()
            .build();
    }