รบกวนถาม : เขียน code เสร็จแล้ว ไม่มี error หรือ warning แต่พอรันแล้ว เกิด error ใน emolater android

package com.example.feeprice;

import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.graphics.Typeface;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;


public class MainActivity extends Activity {

	private EditText ePrice;
	private EditText eDiscount;
	private EditText eTax;
	
	private Button   bAdd;
	private Button   bMinus;
	private Button   bDel;
	private Button   bCal;
	
	String   eStart;
	
	private Context context;
	
	private Typeface thaifont;
	//for set double
	private Double editStartD=0D;
	private Double priceAfterDis=0D;
	private Double priceForSale=0D;
	
	private Double disCountNum=0D;
	private Double disCountCost=0D;
	private Double taxNum=0D;
	Double taxPrice=0D;
	//for set text show word
	private TextView txtPrice;
	private TextView txtDiscount;
	private TextView txtAfterDis;
	private TextView txtTax;
	private TextView txtTotal;
	//for set text view display 
	private TextView rPrice;
	private TextView rDiscount;
	private TextView rafdis;
	private TextView rtax;
	private TextView rtotal;
	//for display number
	private TextView shPrice;
	private TextView shDiscount;
	private TextView shafdis;
	private TextView shtax;
	private TextView shtotal;
	
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        ePrice=(EditText) findViewById(R.id.price);
        eDiscount=(EditText) findViewById(R.id.discount);
        eTax=(EditText) findViewById(R.id.tax);
        
        bAdd=(Button) findViewById(R.id.posi);
        bMinus=(Button) findViewById(R.id.nega);
        bDel=(Button) findViewById(R.id.del);
        bCal=(Button) findViewById(R.id.cal);
        
        txtPrice=(TextView) findViewById(R.id.tprice);
        txtDiscount=(TextView) findViewById(R.id.tdiscount);
        txtAfterDis=(TextView) findViewById(R.id.tafdis);
        txtTax=(TextView) findViewById(R.id.ttax);
        txtTotal=(TextView) findViewById(R.id.ttotal);
        
        rPrice=(TextView) findViewById(R.id.spprice);
    	rDiscount=(TextView) findViewById(R.id.spdiscount);
    	rafdis=(TextView) findViewById(R.id.spafdis);
    	rtax=(TextView) findViewById(R.id.sptax);
    	rtotal=(TextView) findViewById(R.id.sptotal);
        
        txtPrice.setTypeface(thaifont);
        txtDiscount.setTypeface(thaifont);
        txtAfterDis.setTypeface(thaifont);
        txtTax.setTypeface(thaifont);
        txtTotal.setTypeface(thaifont);
        
        shPrice.setTypeface(thaifont);
    	shDiscount.setTypeface(thaifont);
    	shafdis.setTypeface(thaifont);
    	shtax.setTypeface(thaifont);
    	shtotal.setTypeface(thaifont);
        
        txtPrice.setText("");
        txtDiscount.setText("");
        txtAfterDis.setText("");
        txtTax.setText("");
        txtTotal.setText("");
        
        
        
       bCal.setOnClickListener(new View.OnClickListener() {
		
		public void onClick(View v) {
			eStart=ePrice.getText().toString();//get text and save to eStart
			
			if(eDiscount.getText().toString().equals(""))
				{eDiscount.setText("0");}  //set discount to "0"
			
			if(ePrice.equals("")){
				Toast t=Toast.makeText(context, "ไม่ใช่ตัวเลข", Toast.LENGTH_SHORT);
				TextView tv=(TextView) t.getView().
						findViewById(android.R.id.message);//message auto generate
				tv.setTypeface(thaifont);
				t.show();
			}else{
				editStartD=Double.parseDouble(eStart);
				disCountNum=Double.parseDouble(eDiscount.getText().toString());
				
				if(disCountNum==0){
					priceAfterDis=editStartD;			
				}else{
					priceAfterDis=editStartD-(editStartD*(disCountNum/100.0));
					disCountCost=editStartD*(disCountNum/100.0);
					taxNum=Double.parseDouble(eTax.getText().toString());
					taxPrice=priceAfterDis*(taxNum/100.0);
					priceForSale=priceAfterDis+(priceAfterDis*(taxNum/100.0));
					
				}
				 txtPrice.setText("\t\t\t\tราคาตั้งต้น");
				 rPrice.setText(""+editStartD);
				 shPrice.setText("บาท");
				 
			     txtDiscount.setText("\t\t\t\tส่วนลด");
			     rDiscount.setText(""+disCountCost);
			     shDiscount.setText("บาท");
			     
			     txtAfterDis.setText("\t\t\t\tราคาหลังส่วนลด");
			     rafdis.setText(""+priceAfterDis);
			     shafdis.setText("บาท");
			     
			     txtTax.setText("\t\t\t\tภาษี");
			     rtax.setText(""+taxNum);
			     shtax.setText("บาท");
			     
			     txtTotal.setText("\t\t\t\tราคาขาย");
			     rtotal.setText(""+priceForSale);
			     shtotal.setText("บาท");
			
			}
					
		}
	});
       
       bDel.setOnClickListener(new View.OnClickListener() {
		
		public void onClick(View v) {
			AlertDialog.Builder dialog=new AlertDialog.Builder(context);
			dialog.setMessage("Delete all");
			
			dialog.setPositiveButton("yes",new OnClickListener(){

				public void onClick(DialogInterface dialog, int which) {
					ePrice.setText("");
					eDiscount.setText("");
					eTax.setText("");
					
					 txtPrice.setText("\t\t\t\tราคาตั้งต้น");
					 shPrice.setText("บาท");
					txtDiscount.setText("\t\t\t\tส่วนลด");
					shDiscount.setText("บาท");
					txtAfterDis.setText("\t\t\t\tราคาหลังส่วนลด");
					 shafdis.setText("บาท");
					 txtTax.setText("\t\t\t\tภาษี");
					shtax.setText("บาท");
					txtTotal.setText("\t\t\t\tราคาขาย");
					 shtotal.setText("บาท");
					
				}			
			});
			dialog.setNegativeButton("no",new OnClickListener(){

				public void onClick(DialogInterface dialog, int which) {
					dialog.dismiss();
					
				}
				
			} );
			dialog.show();
			
		}
	});
       
        bAdd.setOnClickListener(new View.OnClickListener() {
			
			public void onClick(View v) {
				int plus=Integer.parseInt(eDiscount.getText().toString());
				plus++;
				
				eDiscount.setText(String.valueOf(plus));
				
			}
		});
        
        bMinus.setOnClickListener(new View.OnClickListener() {
			
			public void onClick(View v) {
				int plus=Integer.parseInt(eDiscount.getText().toString());
				plus--;
				
				if(plus<=0){plus=0;}
				
				eDiscount.setText(String.valueOf(plus));
			}
		});       
    }
    
}