Need help for my android app - Converter

int mPosition;
TextView textView = (TextView) findViewById(R.id.textView3);
EditText editFieldOne = (EditText) findViewById(R.id.editKms);        
EditText editFieldTwo = (EditText) findViewById(R.id.editMiles);        
Button buttonConvert = (Button) findViewById(R.id.buttonConvert);
Spinner spinnerKmMile = (Spinner) findViewById(R.id.spinner1);

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);        
    setContentView(R.layout.activity_main);

    ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(getApplicationContext(), 
            R.array.spinner_array, android.R.layout.simple_spinner_item);
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

    spinnerKmMile.setAdapter(adapter);
    spinnerKmMile.setOnItemSelectedListener(new OnSpinnerItemSelect());

    buttonConvert.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {               
            handleConvertCalculation();                         
        }           
    });
}   
public class OnSpinnerItemSelect implements OnItemSelectedListener {

    @Override
    public void onItemSelected(AdapterView<?> parent, View arg1, int position,
            long id) {
        mPosition = position;
        switch (mPosition) {
        case 0:
            String str1 = parent.getItemAtPosition(1).toString();
            textView.setText(str1);
            break;
        case 1:
            String str2 = parent.getItemAtPosition(0).toString();
            textView.setText(str2);
            break;
        default:
            break;
        }
    }

    @Override
    public void onNothingSelected(AdapterView<?> arg0) {
        // Auto-generated method stub
    }
}
public void handleConvertCalculation() {
    if (mPosition == 0) {
        try {                   
            double kms = Double.valueOf (editFieldOne.getText().toString());                
            double miles = kms * 0.621371192;                   
            editFieldTwo.setText(String.valueOf(miles));        
        }                   
        catch (Exception e) {   
            editFieldTwo.setText("");
            Toast.makeText(getApplicationContext(), "Enter a number!", 
                                                Toast.LENGTH_LONG).show();                  
        }
    }
    else if (mPosition == 1) {
        try {                   
            double miles = Double.valueOf (editFieldOne.getText().toString());              
            double kms = miles * 1.609344;                  
            editFieldTwo.setText(String.valueOf(kms));      
        }                   
        catch (Exception e) {   
            editFieldTwo.setText("");
            Toast.makeText(getApplicationContext(), "Enter a number!", 
                                                Toast.LENGTH_LONG).show();  
        }
    }
    else {
        Toast.makeText(getApplicationContext(), "Bug in Code! mPosition = " +
                mPosition, Toast.LENGTH_LONG).show();
    }
}