How to use Android Billing Library?

https://github.com/robotmedia/AndroidBillingLibrary

I've created separate Billing class:

public class Billing extends AbstractBillingActivity {
    private static final String TAG = "Billing";

    public Billing() {
    }

    @Override
    public void onBillingChecked(boolean supported) {
        Log.i(TAG, "Billing supported开发者_运维知识库: " + supported);
    }

once user presses button in Preferences I do:

    Preference buyPref = (Preference) findPreference("pref_billing_buy");
    buyPref.setOnPreferenceClickListener(new OnPreferenceClickListener() {
        public boolean onPreferenceClick(Preference preference) {   
            if (Debug.Yes) Log.d(TAG, "Buying ad-free version");
            Billing billing = new Billing();
            billing.checkBillingSupported();

            return true;
        }
    });

and getting the following error:

07-04 20:21:22.797: ERROR/AndroidRuntime(7172): FATAL EXCEPTION: main
07-04 20:21:22.797: ERROR/AndroidRuntime(7172): java.lang.NullPointerException
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.content.ContextWrapper.getPackageName(ContextWrapper.java:120)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at net.robotmedia.billing.BillingService.getActionForIntent(BillingService.java:76)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at net.robotmedia.billing.BillingService.createIntent(BillingService.java:69)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at net.robotmedia.billing.BillingService.checkBillingSupported(BillingService.java:58)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at net.robotmedia.billing.BillingController.checkBillingSupported(BillingController.java:114)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at net.robotmedia.billing.AbstractBillingActivity.checkBillingSupported(AbstractBillingActivity.java:42)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at spb.bridges.Preferences$1.onPreferenceClick(Preferences.java:212)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.preference.Preference.performClick(Preference.java:812)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.preference.PreferenceScreen.onItemClick(PreferenceScreen.java:198)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.widget.AdapterView.performItemClick(AdapterView.java:284)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.widget.ListView.performItemClick(ListView.java:3382)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.widget.AbsListView$PerformClick.run(AbsListView.java:1696)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.os.Handler.handleCallback(Handler.java:587)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.os.Handler.dispatchMessage(Handler.java:92)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.os.Looper.loop(Looper.java:144)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at android.app.ActivityThread.main(ActivityThread.java:4937)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at java.lang.reflect.Method.invokeNative(Native Method)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at java.lang.reflect.Method.invoke(Method.java:521)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
07-04 20:21:22.797: ERROR/AndroidRuntime(7172):     at dalvik.system.NativeStart.main(Native Method)

What is wrong in my code?

Also, documentation says

When started your AbstractBillingActivity subclass will check if in-app billing is supported, followed by a call to onBillingChecked(boolean), which has to be implemented by the subclass.

But actually onBillingChecked() is not called.

I should be reading documentation more carefully:

AbstractBillingActivity is an abstract activity that provides default integration with in-app billing.

So, it is started to work when I've replaced in my code extends Activity with extends AbstractBillingActivity (actually since I've used PreferenceActivity, not just Activity, I had to edit AbstractBillingActivity also).