Android ขอถามเรื่องการเพิ่มค่าในตัวแปรจากการใช้ button onClick หน่อยครับ

package com.myapp;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.app.AlertDialog;

public class MainActivity extends Activity {
	
    int iNum;  
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

	iNum = 0;
        
        final AlertDialog.Builder adb = new AlertDialog.Builder(this);
        
        final Button btn1 = (Button) findViewById(R.id.button1);
        // Perform action on click
        btn1.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                iNum = iNum + 1;
            }
        });
        
        final Button btn2 = (Button) findViewById(R.id.button2);
		// Perform action on click
        btn2.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                iNum = iNum - 1;
            }
        });
        
    }
    
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
	
}

package app.account;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.security.PublicKey;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.StatusLine;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;

import android.R.integer;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Point;
import android.os.Bundle;
import android.os.StrictMode;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;

public class Tabbalance extends Activity{
	int NumDay;
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.totalmoney);
	
		
		  if (android.os.Build.VERSION.SDK_INT > 9) {
	            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
	            StrictMode.setThreadPolicy(policy);
	        }
			
		  databalance();	
}

	private void databalance() {
		// TODO Auto-generated method stub
		
		NumDay = 0;
		
		 ImageButton btnBackDay = (ImageButton)findViewById(R.id.btnBackday);
			btnBackDay.setOnClickListener(new OnClickListener() {
				
				@Override
				public void onClick(View v) {
					NumDay = NumDay+1;
					
				}
			});
			ImageButton btnNeckDay = (ImageButton)findViewById(R.id.btnNextday);
			btnNeckDay.setOnClickListener(new OnClickListener() {
				
				@Override
				public void onClick(View v) {
					// TODO Auto-generated method stub
					NumDay = NumDay-1;
					Toast.makeText(getBaseContext(), NumDay, Toast.LENGTH_LONG).show();
				}
			});
		
		final TextView txttotal = (TextView)findViewById(R.id.totalmoney);
		final TextView txtinput = (TextView)findViewById(R.id.totalinput);
		final TextView txtoutput = (TextView)findViewById(R.id.totaloutput);
		final TextView txtsummary = (TextView)findViewById(R.id.totalsummary);
		final TextView txtday  = (TextView)findViewById(R.id.txtDay);
		
		final String Day = (String.valueOf(NumDay));
		
		Toast.makeText(getBaseContext(), Day, Toast.LENGTH_LONG).show();
	
		// TODO Auto-generated method stub
    	Intent intent= getIntent();
    	final String Mid = intent.getStringExtra("MemberID");
    	
    	String url = "----------------------------";
    	
    	List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("mid", Mid));
        params.add(new BasicNameValuePair("mid", Day));
        
        
        String Server = getJSONUrl(url, params);
        	
        String stramount = "" ;
        String strinput = "";
        String stroutput = "";
        String strsummary = "";
        String strday = "";

        
        JSONObject c;
    	try {
    		c = new JSONObject(Server);
    		stramount = c.getString("amount");
    		strinput = c.getString("input");
    		stroutput = c.getString("output");
    		strsummary = c.getString("summary");
    		strday = c.getString("date");
    		
    		
    	if(!Mid.equals("")){
    		txttotal.setText(stramount);
    		txtinput.setText(strinput);
    		txtoutput.setText(stroutput);
    		txtsummary.setText(strsummary);
    		txtday.setText(strday);
    	}
    	else{
    		txttotal.setText("");
    		txtinput.setText("");
    		txtoutput.setText("");
    		txtsummary.setText("");
    		txtday.setText("");    		
    	}
    		

    	} catch (JSONException e) {
    		// TODO Auto-generated catch block
    		e.printStackTrace();
    	}
    }
 
public String getJSONUrl(String url,List<NameValuePair> params) {
	StringBuilder str = new StringBuilder();
	HttpClient client = new DefaultHttpClient();
	HttpPost httpPost = new HttpPost(url);
	
	try {
		httpPost.setEntity(new UrlEncodedFormEntity(params));
		HttpResponse response = client.execute(httpPost);
		StatusLine statusLine = response.getStatusLine();
		int statusCode = statusLine.getStatusCode();
		if (statusCode == 200) { // Download OK
			HttpEntity entity = response.getEntity();
			InputStream content = entity.getContent();
			BufferedReader reader = new BufferedReader(new InputStreamReader(content));
			String line;
			while ((line = reader.readLine()) != null) {
				str.append(line);
			}
		} else {
			Log.e("Log", "Failed to download file..");
		}
	} catch (ClientProtocolException e) {
		e.printStackTrace();
	} catch (IOException e) {
		e.printStackTrace();
	}
	return str.toString();
}
}