Cant access cursor from a class android

Question

I am trying to access cursor in a class which needs a context to call and need a activity to start startManagingCursor function.

In a activity i called my class like this.

backupSMS b=new backupSMS(getBaseContext(),backupOptions.this);
b.BackUpAllSms();

and i wrote backupSMS class like this:

public class backupSMS {

    Context context;
    Activity myActivity;

    public backupSMS(Context con, Activity application) {
        context = con;
        myActivity = application;

        Log.d("context", "con: " + context + " act: " + myActivity);
        BackUpAllSms();
    }

    @SuppressWarnings("deprecation")
    public void BackUpAllSms() {

        ArrayList<SmsDataClass> all_sms_data = new ArrayList<SmsDataClass>();

        // backup all sms
        Uri uri = Uri.parse("content://sms");
        Cursor c = context.getContentResolver().query(uri, null, null, null,
                null);
        myActivity.startManagingCursor(c);

        // Read the sms data and store it in the list
        if (c.moveToFirst()) {
            for (int i = 0; i < c.getCount(); i++) {

                SmsDataClass sms = new SmsDataClass();

                sms.setAddress(c.getString(c.getColumnIndexOrThrow("address"))
                        .toString());
                sms.setBody(c.getString(c.getColumnIndexOrThrow("body"))
                        .toString());

                all_sms_data.add(sms);

                c.moveToNext();
            }
        }
        c.close();
    }
}

But it shows a nullpointer exception. But if i write the BackUpAllSms() function into my backupOptions activity then it works fine. What is the problem here ??

My logCat:

     FATAL EXCEPTION: main
 java.lang.NullPointerException
    at com.example.smsbackup.backupSMS.BackUpAllSms(backupSMS.java:74)
    at com.example.smsbackup.backupSMS.<init>(backupSMS.java:51)
    at com.example.smsbackup.backupOptions$3.onClick(backupOptions.java:67)
    at android.view.View.performClick(View.java:4212)
    at android.view.View$PerformClick.run(View.java:17476)
06-13 11:42:19.205: E/AndroidRuntime(12771):    at android.os.Handler.handleCallback(Handler.java:800)
06-13 11:42:19.205: E/AndroidRuntime(12771):    at android.os.Handler.dispatchMessage(Handler.java:100)
06-13 11:42:19.205: E/AndroidRuntime(12771):    at android.os.Looper.loop(Looper.java:194)
06-13 11:42:19.205: E/AndroidRuntime(12771):    at android.app.ActivityThread.main(ActivityThread.java:5371)
06-13 11:42:19.205: E/AndroidRuntime(12771):    at java.lang.reflect.Method.invokeNative(Native Method)
06-13 11:42:19.205: E/AndroidRuntime(12771):    at java.lang.reflect.Method.invoke(Method.java:525)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
    at dalvik.system.NativeStart.main(Native Method)

Answer 1

First thing first, this part of your code:

backupSMS b=new backupSMS(getBaseContext(), backupOptions.this);

..and therefore your backupSms class' constructor, is redundant. Activity extends Context, so they're pretty much the same thing. You should just make the constructor like this:

private Activity mActivity;

public backupSms(Activity a) {
    mActivity = a;
}

And use mActivity for every operation that might need throughout the class.

Also, call this when creating backupSms:

backupSMS b=new backupSMS(this);