求解。我写的一个Android程序如何修改

public class MainActivity extends Activity {
EditText edittext1;
EditText edittext2;
Button button1;
Button button2;
mysqlite myHelper;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    edittext1=(EditText)findViewById(R.id.editText1);
    edittext2=(EditText)findViewById(R.id.editText2);
    button1=(Button)findViewById(R.id.button1);
    button2=(Button)findViewById(R.id.button2);
    myHelper=new mysqlite(this,"sam4",null,1);

    button1.setOnClickListener(new  OnClickListener(){
    public void onClick(View view) {
    String text1=edittext1.getText().toString();
    String text2=edittext2.getText().toString();    
    insert();
    }
   }
);
    public void insert(){ 
   SQLiteDatabase db=myHelper.getWritableDatabase();
   String sql="insert into zhf(name,xuehao)values("+edittext1+","+edittext2+")";
   db.execSQL(sql);
   db.close();}       
    button2.setOnClickListener(new  OnClickListener(){
        public void onClick(View view) {
        String text1=edittext1.getText().toString();
        String text2=edittext2.getText().toString();    

        }

}
我现在希望能在两个EditText 的文本框输入相应的账号和密码之后，就能显示登录成功，我应该如何修改

1、
 String sql="insert into zhf(name,xuehao)values("+edittext1+","+edittext2+")";
 改
 String sql="insert into zhf(name,xuehao)values('"+edittext1+"','"+edittext2+"')";
 2、从数据库查找是否用户名密码匹配的账号，如果匹配，则成功。
 http://blog.csdn.net/rhljiayou/article/details/7085347