java – 从其他类调用MainActivity方法(扩展广播接收器)

但得到了这个错误：

java.lang.RuntimeException: Unable to start receiver com.weekendproject.roshu.spamblocker.PhoneStateReceiver: java.lang.NullPointerException: Attempt to invoke virtual method ‘java.lang.String android.content.Context.getPackageName()’ on a null object reference

在MainActivity中专门指向此行的错误

Intent resultIntent = new Intent(getApplicationContext(),MainActivity.class);

但是我试图将getApplicationContext()更改为“this”和“getActivity()”,但它无法正常工作

这是完整的代码

MainActivity.java

public class MainActivity extends ActionBarActivity {

    public void display_notification(String incoming_number) {

    NotificationCompat.Builder mBuilder =
            new NotificationCompat.Builder(getApplicationContext())
                    .setSmallIcon(R.drawable.ic_action)
                    .setContentTitle("SpamBlocker alert !!")
                    .setContentText("SpamBlocker blocked number : " + incoming_number);

    // **Error occured in following line**
    Intent resultIntent = new Intent(getApplicationContext(),MainActivity.class);

    TaskStackBuilder stackBuilder = TaskStackBuilder.create(getApplicationContext());
    stackBuilder.addParentStack(MainActivity.class);
    stackBuilder.addNextIntent(resultIntent);
    PendingIntent resultPendingIntent =
            stackBuilder.getPendingIntent(
                    0,PendingIntent.FLAG_UPDATE_CURRENT
            );
    mBuilder.setContentIntent(resultPendingIntent);
    NotificationManager mNotificationManager =
            (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
    Random r = new Random();
    int rand = r.nextInt(1000);
    mNotificationManager.notify(rand,mBuilder.build());
    }
}

PhoneStateReceiver.java

public class PhoneStateReceiver extends BroadcastReceiver {

    MainActivity mActivity;

    @Override
    public void onReceive(Context context,Intent intent) {
        mActivity = new MainActivity();
        mActivity.display_notification(incomingNumber);           // call main activity methods

    }
}