25/9/8/SQLite/ContentProvider

SQLite

ContentProvider

Android是对SQLite3进行操作的，其操作步骤一般是：

1.首先建立一个Java类继承于SQLiteOpenHelper重写里面的方法

2.在onCreate方法中用sql语句创建一个表

3.在MainActivity中声明这个类，然后调用getWritableDatabase()方法生成一个SQLiteDatabase对象，然后利用这个对象对创建的表进行增删改查的操作

4.代码实现

public class SqliteOpenHelperTest extends SQLiteOpenHelper {
public SqliteOpenHelperTest(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}
public SqliteOpenHelperTest(Context context,String name){
this(context,name,null,1);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table if not exists user (id integer primary key autoincrement ,name varchar(20),password varchar(20)) ");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}
}

private SQLiteDatabase db;
SqliteOpenHelperTest sqlite=new SqliteOpenHelperTest(getApplicationContext(),"SQL_FIRST_DB.db");
db=sqlite.getWritableDatabase();
case R.id.sql_button_insert:
ContentValues value=new ContentValues();
value.put("name",mEditTextUser.getText().toString());
value.put("password",mEditTextPassword.getText().toString());
db.insert("user",null,value);
break;
case R.id.sql_button_updata:
ContentValues value1=new ContentValues();
value1.put("password","0123456");
db.update("user",value1,"name=?",new String[]{"Jinx"});
break;
case R.id.sql_button_delete:
db.delete("user","name=?",new String[]{"Jinx"});
break;
case R.id.sql_button_query:
//                Cursor cursor=db.rawQuery("select * from user", null);
Cursor cursor=db.query("user",null,null,null,null,null,"id DESC","2,4");//2和4 分别表示偏移量和数量DESC表示倒序的方式排列
cursor.moveToFirst();
while (!cursor.isAfterLast()){
String name=cursor.getString(cursor.getColumnIndex("name"));
String password=cursor.getString(cursor.getColumnIndex("password"));
Log.d("cursor","用户名为："+name+"密码为："+password);
cursor.moveToNext();
}
break;

ContentProvider主要用于在不同的应用程序之间实现数据共享的功能，它的基本用法是：

private ArrayAdapter<String> mAdapter;
List<String> mContactsList=new ArrayList<>();
mListView= (ListView) findViewById(R.id.contacts_listview);
mAdapter=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,mContactsList);
mListView.setAdapter(mAdapter);
readContacts();
private void readContacts() {
Cursor cursor=null;
cursor=getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,null,null,null,null);
while (cursor.moveToNext()){
String displyName=cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
String number=cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
mContactsList.add(displyName+"\n"+number);

}
}