مشکل در پروژه Counter استاد

در کلاس G یک فیلد با نام زیر بسازید : 

 public static Activity activity;

بعد به ورودی Dialog این فیلد رو بده بجای context:

 Dialog dialog = new Dialog(G.activity);

 package com.uncocoder.app.course.counter;

import android.app.Dialog;
import android.util.Log;
import android.widget.TextView;


public class ThreadCounter extends Thread {

    private int      seconds;
    private int      counter;
    private TextView textView;


    public void setSeconds(int value) {
        seconds = value;
        counter = seconds;
    }


    public void setTextView(TextView value) {
        textView = value;
    }


    @Override
    public void run() {
        super.run();
        while (counter > 0) {
            try {
                Thread.sleep(1000);
            }
            catch (InterruptedException e) {
                e.printStackTrace();
            }
            counter--;
            if (textView != null) {
                G.HANDLER.post(new Runnable() {

                    @Override
                    public void run() {
                        int min = (int) Math.floor(counter / 60);
                        int sec = counter % 60;

                        String minPrefix = "";
                        if (min < 10) {
                            minPrefix = "0";
                        }

                        String secPrefix = "";
                        if (sec < 10) {
                            secPrefix = "0";
                        }

                        textView.setText(minPrefix + min + ":" + secPrefix + sec);
                    }
                });
            }
            Log.i("LOG", "Counter: " + counter);
        }

        G.HANDLER.post(new Runnable() {

            @Override
            public void run() {
                Dialog dialog = new Dialog(G.activity);
                dialog.setContentView(R.layout.dialog);
                dialog.show();
            }
        });
    }

}

 package com.uncocoder.app.course.counter;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;


public class ActivityMain extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        TextView txtCounter = (TextView) findViewById(R.id.txtCounter);

        ThreadCounter counter = new ThreadCounter();
        counter.setSeconds(5);
        counter.setTextView(txtCounter);
        counter.start();
    }
}

دادا این کد اینم نتیجش

 package mehran.sunofgod.alarm;

import android.app.Activity;
import android.app.Dialog;
import android.os.Bundle;
import android.os.Handler;


public class AlarmActivity extends Activity {

    Handler handler = new Handler();


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Thread th = new Thread(new Runnable() {

            @Override
            public void run() {
                try {
                    Thread.sleep(4000);
                }
                catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                handler.post(new Runnable() {

                    @Override
                    public void run() {
                        Dialog d = new Dialog(AlarmActivity.this);
                        d.setContentView(R.layout.main);
                        d.show();
                    }
                });

            }
        });
        th.start();
    }
}