Android__数据存储

来源：互联网发布：杨辉三角c语言程序六行编辑：程序博客网时间：2024/05/21 10:21

android端的三种数据存储方式：

文件存储
SharedPreference存储
SQLite数据库存储

文件存储：
Context类提供了openFileOutput()的方法，通过java的输出流将数据存储到默认路径
/data/data//files/目录下
提供了InputFileOutput()的方法，通过java的读入流
一般的用户是访问不了手机，必须要有root权限才可以
所以这一部分的内容主要通过模拟器才能显示效果

案例：实现数据的保存和读取，按返回键之后不会消失public class MainActivity extends Activity {    private EditText editText;    protected void onCreate(Bundle savedInstanceState){        super.onCreate(savedInstanceState);        setContentView(R.layout.main_activity);        //初始化        editText = (EditText)findViewById(R.id.editText);        String getinputText = load();        if(!TextUtils.isEmpty(getinputText)){            editText.setText(getinputText);            editText.setSelection(getinputText.length());            Toast.makeText(this, "Restore Success",                    Toast.LENGTH_SHORT).show();        }    }    //保证在销毁之前保存数据    protected void onDestroy(){        super.onDestroy();          String inputText =editText.getText().toString();        savedata(inputText);    }    private void savedata(String inputText) {        FileOutputStream out = null;        BufferedWriter writer = null;        try {            out = openFileOutput("data", Context.MODE_PRIVATE);            writer = new BufferedWriter(new OutputStreamWriter(out));            writer.write(inputText);        } catch (Exception e) {            // TODO: handle exception            e.printStackTrace();        }finally{            if(writer!=null){                try {                    writer.close();                } catch (IOException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }            }        }    }    //从默认的"data"读入，editText.setText(getinputText);    public String load(){        InputStream in =null;        BufferedReader br = null;        StringBuffer sb = new StringBuffer();        try {            in = openFileInput("data");            br = new BufferedReader(new InputStreamReader(in));            String line ="";            while((line=br.readLine())!=null){                sb.append(line);            }        } catch (Exception e) {            // TODO: handle exception            e.printStackTrace();        }finally{            if(br!=null){                try {                    br.close();                } catch (IOException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }            }        }        return sb.toString();    }}

SharedPreference存储

以键值对的方式存储数据

获取SharedPreference对象的三种方法：
1 Context类下的getSharedPreferences()
2 Activity类的getPreferences()
3 PreferenceManager类的getDefaultSharedPreferences()

得到对象之后

存储过程分三步实现：
1 调用SharedPreference对象下的edit()方法获取一个SharedPreference.Edit对象
SharedPreference.Editor editor =
getSharedPreferences(“data”,MODE_PRIVATE).edit();
2 添加数据
editor.putString(“name”,”Tom”);
3 提交数据commit()
editor.commit();

读取过程：
创建SharedPreferences pref = getSharedPreferences(“data”,MODE_PRIVATE);

String name = pref.getString(“name”,”“);

用getString(key,defaultValue),
getInt(key,defaultValue),
getBoolean(key,defaultValue)等方法
获取对应的数据

实现记住密码功能：

public class LoginActivity extends Activity {    private EditText accountEditText;    private EditText passwordEditText;    private Button loginButton;    //复选框控件    private CheckBox rememberPasswordBox;    //存储    private SharedPreferences sharedPreferences;    private SharedPreferences.Editor editor;    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.login);        sharedPreferences = PreferenceManager                .getDefaultSharedPreferences(LoginActivity.this);        accountEditText = (EditText) findViewById(R.id.account);        passwordEditText = (EditText) findViewById(R.id.password);        loginButton = (Button) findViewById(R.id.login_button);        rememberPasswordBox = (CheckBox) findViewById(R.id.check_password);        boolean rememberPassword = sharedPreferences.getBoolean("remember_password", false);        if(rememberPassword){            String account = sharedPreferences.getString("account", "");            String password = sharedPreferences.getString("password", "");            accountEditText.setText(account);            passwordEditText.setText(password);            rememberPasswordBox.setChecked(true);        }        loginButton.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                // TODO Auto-generated method stub                String account = accountEditText.getText().toString();                String password = passwordEditText.getText().toString();                if (account.equals("admin") && password.equals("admin")) {                    editor = sharedPreferences.edit();                    //复选框是否被勾中监听机制                    if(rememberPasswordBox.isChecked()){                        editor.putBoolean("remember_password", true);                        editor.putString("account", account);                        editor.putString("password", password);                    }else{                        editor.clear();                    }                    //别忘记提交                    editor.commit();//                  Toast.makeText(LoginActivity.this, "login success",//                          Toast.LENGTH_SHORT).show();                    Intent intent = new Intent(LoginActivity.this,SucessActivity.class);                    startActivity(intent);                } else {                    Toast.makeText(LoginActivity.this,                            "account or password error", Toast.LENGTH_SHORT)                            .show();                }            }        });    }}

SQLite数据库存储:
SQLite是一种轻量级的关系型数据库
可以存储各种类型的文件

其操作和MySQL的语法基本相同

四种数据类型：
integer 整型 real浮点型 text 文本类型 blob 二进制型

创建数据库，插入一个表
先新建一个MyDatabase extends SQLiteOpenHelper
SQLiteOpenHelper是一个数据库管理器，负责对数据库的创建和表的创建，更新等操作

public class MyDatabase extends SQLiteOpenHelper {

public static final String CREATE_BOOK ="create table Book("        + "id integer primary key autoincrement,"        + "author text,"        + "pages integer,"        + "name text,"        + "price real)";//在这里随便添加语句，并在//public void onUpgrade()更新，只有修改版本号大于旧版本号的时候才会进行更新操作//private Context mContext;

public MyDatabase(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
// TODO Auto-generated constructor stub
mContext = context;
}

//如果数据库已经创建，而且table也创建了，你下一次就不会重复执行这个方法了@Overridepublic void onCreate(SQLiteDatabase db) {    // TODO Auto-generated method stub    db.execSQL(CREATE_BOOK);    Toast.makeText(mContext, "create database success",             Toast.LENGTH_SHORT).show();}//只有当版本出现更新的时候才会进行调用这个方法    @Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {    // TODO Auto-generated method stub    switch(oldVersion){    case 1:db.execSQL(CREATE_BOOK_CATEGORY2);    default:    }}

}

接着在MainActivity中public class MainActivity extends Activity {//  private MyDatabase dbHelper;//  protected void onCreate(Bundle savedInstanceState){//      super.onCreate(savedInstanceState);//      setContentView(R.layout.main_activity);//      //      //初始化数据库，创建数据库BookStore.db//      //改变版本号就可以//      //public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){}；//      dbHelper = new MyDatabase(this, "BookStore.db", null,1);//      //      Button createdatabase =(Button)findViewById(R.id.button);//      createdatabase.setOnClickListener(new OnClickListener() {//          //          @Override//          public void onClick(View v) {//              // TODO Auto-generated method stub//              dbHelper.getWritableDatabase();////                //              //          }//      });}

以下是一些在MainActivity的SQLite语句添加，插入//      Button addData = (Button)findViewById(R.id.add);//      addData.setOnClickListener(new OnClickListener() {//          //          @Override//          public void onClick(View v) {//              // TODO Auto-generated method stub//              SQLiteDatabase db = dbHelper.getWritableDatabase();//              ContentValues values = new ContentValues();//              //              //开始组装数据//              values.put("name", "The Da Vinci Code");//              values.put("author", "Dan Brown");//              values.put("pages", 454);//              values.put("price",15);//              //              db.insert("Book", null, values);//              values.clear();//              //              values.put("name", "The Lost Symbol");//              values.put("author", "Dan Brown");//              values.put("pages", 510);//              values.put("price",19);//              //              //              db.insert("Book", null, values);//              //              Toast.makeText(MainActivity.this, "insert ok",//                      Toast.LENGTH_SHORT).show();//              //          }//      });修改db.update("Book", values, "name=?", new String[]{"The Da Vinci Code"});删除//？占位符    1参数名称//  db.delete("Book", "id>?", new String[]{"1"});查询Button query = (Button)findViewById(R.id.query);//      //      query.setOnClickListener(new OnClickListener() {//          //          int count=0;//          //          @Override//          public void onClick(View v) {//              count++;//              // TODO Auto-generated method stub//              SQLiteDatabase db = dbHelper.getWritableDatabase();//              //              //查表自定义//              Cursor cursor = db.query("Book", null, null, null, null, null, null);//              //              if(cursor.moveToFirst()){//从第个迭代开始//                  do{//                      if(count>=2){//                          break;//                      }//                      //遍历Cursor对象，取出数据并打印//                      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"));//                      //                      Toast.makeText(MainActivity.this, "name: "+name+" author: "+author//                              +" price: "+price+" pages: "+pages, Toast.LENGTH_SHORT).show();//                      //                      //                  }while(cursor.moveToNext());//                  //                  //              }//          }//      });代替，事务操作，特别是关于重要的数据操作，如银行Button replace = (Button)findViewById(R.id.replace_data);//      replace.setOnClickListener(new OnClickListener() {//          //          @Override//          public void onClick(View v) {//              // TODO Auto-generated method stub//              SQLiteDatabase db = dbHelper.getWritableDatabase();//              //              db.beginTransaction();//开始事务//              //              try {//                  db.delete("Book", null, null);////                    if(true){////                        //添加异常，使下面的操作不成功，事务失败////                        throw new NullPointerException();////                    }//                  //                  ContentValues values = new ContentValues();//                  values.put("name", "Sb");//                  values.put("author", "Mr.Sb");//                  values.put("pages", 720);//                  values.put("price", 80.3);//                  //                  db.insert("Book", null, values);//                  db.setTransactionSuccessful();//事务执行成功//              } catch (Exception e) {//                  // TODO: handle exception//                  e.printStackTrace();//              }finally{//                  Toast.makeText(MainActivity.this, "replace ok",//                          Toast.LENGTH_SHORT).show();//                  db.endTransaction();//结束事务//                  //              }//          }//      });

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