Android数据存储--sqlite

SQLite是轻量级的、嵌入式的、关系型数据库，目前已经在iPhone、Android等手机系统中使用，而且被其他的公司广泛使用。

Android SQLite，从Android SDK中可以看到，对数据库的操作都封装好了，

常用的一个类就是ContentValues，类似一个Hashmap存放键值对。

我们一般使用sqlite，自己写个类型继承SQLiteOpenHelper，通过这个类的getWritableDatabase方法，可以获得一个SQLiteDatabase的实例。

进而我们可以实现对数据的基本操作了（增，删，改，查）。

public class DBHelper extends SQLiteOpenHelper {

public final static String DB_NAME="contact";
public final static int VERSION=1;
private static DBHelper instance=null;

private  SQLiteDatabase db;
public static DBHelper getInstance(Context context){
if(instance==null)
{
instance=new DBHelper(context);
}
return instance;
}

private void openDatabase()
{
db=this.getWritableDatabase();
}

public DBHelper(Context context){
super(context,DB_NAME,null,VERSION);
// TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub

StringBuffer tableUserCreate =new StringBuffer();

tableUserCreate.append("create table User (id integer primary key autoincrement,")
.append("name text,")
.append("phonenumber text)");

}

@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
// TODO Auto-generated method stub
String sql="drop table if exists user";

db.execSQL(sql);
onCreate(db);
}
//增加一个user
public  boolean saveUser(User user)
{      openDatabase();
ContentValues value=new ContentValues();
String phonenumber = user.getPhoneNumber();
System.out.println("pjoneId:"+phonenumber);
Cursor cursor = db.query("User", new String []{"id","phonenumber","name"} , "phonenumber=?",new String[]{phonenumber} , null, null, null);
cursor.moveToNext();
System.out.println("count:"+cursor.getCount());
if(cursor.getCount()==0)
{
value.put("name", user.getName());
value.put("phonenumber", user.getPhoneNumber());
db.insert("User", null, value);
System.out.println("save");
}
System.out.println("no save");
if(cursor!=null){
cursor = null;
db.close();
}
return true;
}

//获取数据库中所有的user
public List<Map<String, Object>> getUser(){
openDatabase();
List<Map<String,Object>> list = new ArrayList<Map<String,Object>>();
Cursor cursor = db.query("User", new String []{"id","name","phonenumber"} , null, null, null, null, null);
if(cursor!=null){
if(cursor.isBeforeFirst()){
while(cursor.moveToNext())
{
Map<String,Object> map = new HashMap<String, Object>();
map.put("name",cursor.getString(cursor.getColumnIndex("name"));
map.put("id",cursor.getString(cursor.getColumnIndex("id")));
map.put("phonenumber",cursor.getString(cursor.getColumnIndex("phonenumber")));

list.add(map);
}

}
}
if(cursor!=null){
cursor = null;
db.close();
}
return list;
}

//修改user信息
public boolean editUser(User user) {
// TODO Auto-generated method stub
openDatabase();
ContentValues cv = new ContentValues();
cv.put("phonenumber ",user.getPhoneNumber());
cv.put("name", user.getName());
db.update("user", cv, "id=+'"+user.getId()+"'" , null);
db.close();
return true;
}

//取user中的某一字段
public String getUserName(String phonenumber) {
// TODO Auto-generated method stub
openDatabase();
String name = null;
Cursor cursor = db.query("User", new String []{"name"}, "phonenumber='" + phonenumber + "'", null, null, null, null);
if(cursor.isBeforeFirst()){
while(cursor.moveToNext())
{
name = cursor.getString(cursor.getColumnIndex("name"));
System.out.println("name="+name);
}
}
if(cursor!=null){
cursor = null;
db.close();
}
return name;
}
//按条件删除user
public boolean deleteUserById(int id) {
// TODO Auto-generated method stub
openDatabase();
db.delete("User","id='"+id+"'", null);
System.out.println("true");
db.close();
return true;
}

@Override
public String getUserNumber(String str) {
// TODO Auto-generated method stub
openDatabase();
String number = null;
Cursor cursor = db.query("User", new String []{"phonenumber"}, "name='" + str + "'", null, null, null, null);
if(cursor.isBeforeFirst()){
while(cursor.moveToNext())
{
number = cursor.getString(cursor.getColumnIndex("name"));
System.out.println("number="+number);
}
}
if(cursor!=null){
cursor = null;
db.close();
}
return number;
}

}