标签:comm defaults tables pen while shell dex 增删改查 blog
数据持久化:
1、文件存储
适合用于存储一些简单的文本数据或二进制数据
存储数据:openFileOutput(文件名,操作模式),返回值为一个FileOutputStream对象,借助FileOutputStream对象构建出OutputStreamWriter对象,再借助OutputStreamWriter构建出一个BufferedWriter对象,通过bufferedWriter对象将文本写入到文件中。
public void save(){ String data = "data to save"
FileOutputStream out = null;
BufferedWriter writer = null;
try{
out = openFileOutput("data",Context.MODE_PRIVATE);
writer = new BufferedWriter(new OutputStreamWriter(out));
writer.write(data);
}catch(IOException e){
e.printStackTrace();
}finally{
try{
if(writer != null){
writer.close();
}catch(IOException e){
e.printStackTrace();
}
}
}
}
读取数据:openFileInput(文件名),返回FileInputStream对象。
Public String load(){
FileInputStream in = null;
BufferedReader reader = null;
StringBuilder content = new StringBuilder();
try{
in = openFileInput("data");
reader = new BufferedReader(new InputStreamReader(in));
String line = "";
while((line = reader.readLine())!=null){
content.append(line);
}
}catch(IOException e){
e.printStackTrace();
}finally{
if(reader != null){
try{
reader.close();
}catch(IOException e){
e.printStackTrace();
}
}
}
return content.toString();
}
2、SharedPreferences存储
键值对。
获得SharePreferences对象那个的方法
(1)getSharedPreferences(文件名,操作模式)
(2)getPreferences(文件名)
(3)getDefaultSharePreferences(Context)
存储数据:
(1)调用edit()获取一个SharedPreferences.Editor对象
(2)向SharedPreferences.Editor中添加数据
(3)调用commit()提交数据
读取数据:
getXXX(键,默认值)方法
SQLite数据库
创建:通过SQLiteOpenHelper帮助类实现创建和升级。
getReadableDatabase()和getWritableDatabase()
DOS窗口操作SQLite数据库?
1)adb shell
2)ls
3)cd 数据表的路径
4)sqlite3 数据库完整的名字
4.1) .tables
4.2) select * from notetab;
4.3) .exit
4.4) .help
升级:更新版本号
增删改查
增:insert(表名,null,ContentValues对象)
改:updata(表名,ContentValues对象,某一行或几行的数据)
删:delete(表名,某一行或某几行的数据)
查:query(表名,哪列,某一行或几行的数据,group by的列,过滤,排序方式),返回一个Cursor对象
事务:保证一系列的操作要么完成,要么一个都不完成。
(1)调用beginTransaction()开启事务
(2)在异常捕获代码块中执行具体的数据库操作
(3)调用setTransactionSuccessful()表示执行成功
(4)endTransaction()结束事务
public class MainActivity extends Activity { private MyDatabaseHelper dbHelper; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); dbHelper = new MyDatabaseHelper(this,"BookStore.db",null,2); Button createDatabase = (Button) findViewById(R.id.create_database); createDatabase.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { dbHelper.getWritableDatabase(); } }); Button addData = (Button) findViewById(R.id.add_data); addData.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { SQLiteDatabase db = dbHelper.getWritableDatabase(); ContentValues values = new ContentValues(); values.put("name","The Da Vinci Code"); values.put("author","Dan Brown"); values.put("pages","100"); values.put("price","30"); db.insert("Book",null,values); values.clear(); values.put("name","世界末日"); values.put("author","死神"); values.put("pages","10000"); values.put("price","50000"); db.insert("Book",null,values); } }); Button updataData = (Button) findViewById(R.id.updata_data); updataData.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { SQLiteDatabase db = dbHelper.getWritableDatabase(); ContentValues values = new ContentValues(); values.put("price","200"); db.update("Book",values,"name = ?",new String[]{"Tea Da Vinci Code"}); } }); Button deleteData = (Button) findViewById(R.id.delete_data); deleteData.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { SQLiteDatabase db = dbHelper.getWritableDatabase(); db.delete("Book","pages<?",new String[]{"450"}); } }); Button quertData = (Button) findViewById(R.id.query_data); quertData.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { SQLiteDatabase db = dbHelper.getWritableDatabase(); Cursor cursor = db.query("Book",null,null,null,null,null,null); if (cursor.moveToFirst()){ do{ String name = cursor.getString(cursor.getColumnIndex("name")); String author = cursor.getString(cursor.getColumnIndex("author")); int pages = cursor.getInt(cursor.getColumnIndex("pages")); double price = cursor.getDouble(cursor.getColumnIndex("price")); Log.i("XYZ","book name is"+name); Log.i("XYZ","book author name is"+author); Log.i("XYZ","book pages is"+pages); Log.i("XYZ","book price is"+price); }while (cursor.moveToNext()); } cursor.close(); } }); Button replaceData = (Button) findViewById(R.id.replace_data); replaceData.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { SQLiteDatabase db = dbHelper.getWritableDatabase(); db.beginTransaction(); //开启事务 db.delete("Book",null,null); if (true){ throw new NullPointerException(); } ContentValues values = new ContentValues(); values.put("name","游戏大全"); values.put("author","老三"); values.put("pages","20"); values.put("price","35.5"); db.insert("Book",null,values); db.setTransactionSuccessful(); //事务执行成功 db.endTransaction(); //结束事务 } }); } }
标签:comm defaults tables pen while shell dex 增删改查 blog
原文地址:http://www.cnblogs.com/yl-saber/p/6098497.html