android实现记住用户名和密码以及自动登录

package com.sdufe.login;
 
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;
 
/**
 * @author lili.guo
 *
 * 2014-6-6下午3:20:17
 */
public class MainActivity extends Activity {
 
 private EditText username_et;
 private EditText password_et;
 private CheckBox rem;
 private CheckBox auto;
 private Button login;
 private String username,password;
 SharedPreferences sp;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 
 sp=getSharedPreferences("userInfo",Context.MODE_WORLD_READABLE);
 
 username_et=(EditText) findViewById(R.id.username);
 password_et=(EditText) findViewById(R.id.password);
 rem=(CheckBox) findViewById(R.id.remember);
 auto=(CheckBox) findViewById(R.id.autologin);
 login=(Button) findViewById(R.id.login);
 
 if (rem.isChecked()) {
 
 username_et.setText(sp.getString("username", ""));
 password_et.setText(sp.getString("password", ""));
 
 if (auto.isChecked()) {
 Intent intent1=new Intent();
 intent1.setClass(getApplicationContext(), Welcome.class);
 startActivity(intent1);
 }
 
 }
 
 login.setOnClickListener(new View.OnClickListener() {
 
 @Override
 public void onClick(View v) {
 // TODO Auto-generated method stub
 username=username_et.getText().toString();
 password=password_et.getText().toString();
 
 if (username.equals("Thea")&&password.equals("123")) {
  
  Toast.makeText(getApplicationContext(), "登录成功", Toast.LENGTH_SHORT).show();
  
  if (rem.isChecked()) {
  Editor editor=sp.edit();
  editor.putString("username", username);
  editor.putString("password", password);
  editor.commit();
  }
  
  Intent intent2=new Intent();
  intent2.setClass(getApplicationContext(), Welcome.class);
  startActivity(intent2);
 }
 
 
 }
 });
 }
 
 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
 // Inflate the menu; this adds items to the action bar if it is present.
 getMenuInflater().inflate(R.menu.main, menu);
 return true;
 }
 
}

if (rem.isChecked()) {
 
 username_et.setText(sp.getString("username", ""));
 password_et.setText(sp.getString("password", ""));
 
 if (auto.isChecked()) {
 Intent intent1=new Intent();
 intent1.setClass(getApplicationContext(), Welcome.class);
 startActivity(intent1);
 }
 
 }

if (rem.isChecked()) {
  Editor editor=sp.edit();
  editor.putString("username", username);
  editor.putString("password", password);
  editor.commit();
  }
  
  Intent intent2=new Intent();
  intent2.setClass(getApplicationContext(), Welcome.class);
  startActivity(intent2);