Tutorial de Android 3: Terminando la App.

Agregamos las operaciones matemáticas que se realizaran cada que el usuario elija una conversión.

codigo:

 package com.example.marius.convertidora;  
 import android.support.v7.app.ActionBarActivity;  
 import android.os.Bundle;  
 import android.view.Menu;  
 import android.view.MenuItem;  
 import android.view.View;  
 import android.widget.AdapterView.OnItemSelectedListener;  
 import android.widget.AdapterView;  
 import android.widget.ArrayAdapter;  
 import android.widget.EditText;  
 import android.widget.Spinner;  
 import android.widget.Switch;  
 import android.widget.TextView;  
 public class MainActivity extends ActionBarActivity {  
   int pos;  
   Spinner spinner;  
   @Override  
   protected void onCreate(Bundle savedInstanceState) {  
     super.onCreate(savedInstanceState);  
     setContentView(R.layout.activity_main);  
     spinner=(Spinner) findViewById(R.id.spinner);  
     ArrayAdapter <CharSequence> adapter =ArrayAdapter.createFromResource(this, R.array.conversiones, android.R.layout.simple_spinner_item);  
     adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);  
     spinner.setAdapter(adapter);  
     spinner.setOnItemSelectedListener(new OnItemSelectedListener() {  
       @Override  
       public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {  
         pos=position;  
       }  
       @Override  
       public void onNothingSelected(AdapterView<?> parent) {  
       }  
     });  
   }  
   private void displayMessage(String message){  
     TextView convertirTextView = (TextView) findViewById(R.id.txtResultado);  
     convertirTextView.setText(message);  
   }  
   public void resultado(View view){  
     EditText et1= (EditText)findViewById(R.id.etxValor);  
     if (et1.getText().toString().trim().length()>0){  
       String ed1, converMessage;  
       double cm,in,re1,m,km, c, f;  
       ed1=et1.getText().toString();  
       re1=Double.parseDouble(ed1);  
       switch (pos)  
       {  
         case 0:  
           in=re1/2.54;  
           converMessage="cm= " +re1+"\n in= "+ in;  
           displayMessage(converMessage);  
           break;  
         case 1:  
           cm=re1*2.54;  
           converMessage="in= " +re1+"\n cm= "+ cm;  
           displayMessage(converMessage);  
           break;  
         case 2:  
           m = re1 * 1000;  
           converMessage = "De: " + re1 + "kilometros" + " a" + m + "metros";  
           displayMessage(converMessage);  
           break;  
         case 3:  
           km = re1 / 1000;  
           converMessage = "De: " + re1 + "metros" + " a" + km + " kilometros";  
           displayMessage(converMessage);  
           break;  
         case 4:  
           c = (re1 - 32) / 1.8000;  
           converMessage = "De: " + re1 + " farenheit" + " a" + c + " centigrados";  
           displayMessage(converMessage);  
           break;  
         case 5:  
           f = re1 * 1.8000 + 32;  
           converMessage = "De: " + re1 + " centigrados" + " a" + f + "farenheit";  
           displayMessage(converMessage);  
           break;  
       }  
     }  
     else  
     {  
       String error="valor no valido";  
       displayMessage(error);  
     }  
   }  
   @Override  
   public boolean onCreateOptionsMenu(Menu menu) {  
     // Inflate the menu; this adds items to the action bar if it is present.  
     getMenuInflater().inflate(R.menu.menu_main, menu);  
     return true;  
   }  
   @Override  
   public boolean onOptionsItemSelected(MenuItem item) {  
     // Handle action bar item clicks here. The action bar will  
     // automatically handle clicks on the Home/Up button, so long  
     // as you specify a parent activity in AndroidManifest.xml.  
     int id = item.getItemId();  
     //noinspection SimplifiableIfStatement  
     if (id == R.id.action_settings) {  
       return true;  
     }  
     return super.onOptionsItemSelected(item);  
   }  
 }