数据存储

一、三种方法

SharedPreferences
文件
SQLite

二、SharedPreferences

SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 "
                        + "hh:mm:ss");
                // 存入当前时间
                editor.putString("time", sdf.format(new Date()));
                // 存入一个随机数
                editor.putInt("random", (int) (Math.random() * 100));
                // 提交所有存入的数据
                editor.commit();

// 读取int类型的数据
                int randNum = preferences.getInt("random", 0);

 三、file

private String read()
    {
        try        {
            // 打开文件输入流
            FileInputStream fis = openFileInput(FILE_NAME);
            byte[] buff = new byte[1024];
            int hasRead = 0;
            StringBuilder sb = new StringBuilder("");
            // 读取文件内容
            while ((hasRead = fis.read(buff)) > 0)
            {
                sb.append(new String(buff, 0, hasRead));
            }
            // 关闭文件输入流
            fis.close();
            return sb.toString();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        return null;
    }

private void write(String content)
    {
        try
        {
            // 以追加模式打开文件输出流
            FileOutputStream fos = openFileOutput(FILE_NAME, MODE_APPEND);
            // 将FileOutputStream包装成PrintStream
            PrintStream ps = new PrintStream(fos);
            // 输出文件内容
            ps.println(content);
            // 关闭文件输出流
            ps.close();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

四、读写SD卡

<!--在SD卡中创建与删除文件权限-->
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    <!--在SD卡中写入数据权限-->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

if(!Environment.getExternalStorageState().equals(
       Environment.MEDIA_MOUNTED)){
    System.exit(0);
}

 

ActivityCompat.requestPermissions(this,
        new String[]{Manifest.permission.
        WRITE_EXTERNAL_STORAGE},
        1);

public void onRequestPermissionsResult(
    int requestCode, String[] permissions,
     int[] grantResults) {
    super.onRequestPermissionsResult(requestCode,         permissions, grantResults);
    //允许grantResults [i]值为0  禁止为-1
   if(grantResults[0]==-1) System.exit(0);  
}

File sdCardDir = Environment.
        getExternalStorageDirectory();
File targetFile = new File(sdCardDir.getCanonicalPath()
                + FILE_NAME);RandomAccessFile raf = new RandomAccessFile(
        targetFile, "rw");

 五、

// 打开或创建数据库
        db = openOrCreateDatabase(DB_NAME,  Context.MODE_PRIVATE, null);

        // 创建数据表
        String createTable="CREATE TABLE IF NOT EXISTS " +
                TB_NAME +
                "(_id INTEGER PRIMARY KEY AUTOINCREMENT, " +
                "name VARCHAR(32), " +
                "phone VARCHAR(16), " +
                "email VARCHAR(64))";
        db.execSQL(createTable);

        // 查询数据
        cur=db.rawQuery("SELECT * FROM "+ TB_NAME, null);

        // 若查询结果是空的则写入 2 项测试数据
        if(cur.getCount()==0){
            addData("旗标公司","02-23963257","service@flag.com.tw");
            addData("旗讯公司","02-23214335","service@pcdiy.com.tw");
        }

        adapter=new SimpleCursorAdapter(this,
                R.layout.item, cur,FROM,
                new int[] {R.id.name,R.id.phone,R.id.email}, 0);

        lv=(ListView)findViewById(R.id.lv);
        lv.setAdapter(adapter);
        lv.setOnItemClickListener(this);

        // 调用自定义方法, 重新查询及设置按钮状态
        requery();
    }

    private void addData(String name, String phone, String email) {
        // 创建含 3 个字段的 ContentValues对象
        ContentValues cv=new ContentValues(3);
        cv.put(FROM[0], name);
        cv.put(FROM[1], phone);
        cv.put(FROM[2], email);

        db.insert(TB_NAME, null, cv);
    }

    private void update(String name, String phone, String email, int id) {
        ContentValues cv=new ContentValues(3);
        cv.put(FROM[0], name);
        cv.put(FROM[1], phone);
        cv.put(FROM[2], email);
        // 更新 id 所指的字段
        db.update(TB_NAME, cv, "_id="+id, null);
    }

    // 重新查询的自定义方法
    private void requery() {
        cur=db.rawQuery("SELECT * FROM "+TB_NAME, null);
        //更改 Adapter的Cursor
        adapter.changeCursor(cur);
        if(cur.getCount()==MAX) // 已达上限, 停用新增按钮
            btInsert.setEnabled(false);
        else
            btInsert.setEnabled(true);
        btUpdate.setEnabled(false);    // 停用更新按钮
        btDelete.setEnabled(false);    // 停用删除按钮
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
        // 移动 Cursor 至用户选取的选项
        cur.moveToPosition(position);
        // 读出姓名,电话,Email数据并显示
        etName.setText(cur.getString(
                cur.getColumnIndex(FROM[0])));
        etPhone.setText(cur.getString(
                cur.getColumnIndex(FROM[1])));
        etEmail.setText(cur.getString(
                cur.getColumnIndex(FROM[2])));

        btUpdate.setEnabled(true); // 启用更新按钮
        btDelete.setEnabled(true); // 启用删除按钮
    }

    public void onInsertUpdate(View v){
        String nameStr=etName.getText().toString().trim();
        String phoneStr=etPhone.getText().toString().trim();
        String emailStr=etEmail.getText().toString().trim();
        // 任一字段的内容为空即返回
        if(nameStr.length()==0 ||
                phoneStr.length()==0 ||
                emailStr.length()==0) return;

        if(v.getId()==R.id.btUpdate)   // 单击更新按钮
            update(nameStr, phoneStr, emailStr, cur.getInt(0));
        else                     // 单击新增按钮
            addData(nameStr, phoneStr, emailStr);

        requery();
    }

    // 删除按钮的onClick事件方法
    public void onDelete(View v){
        db.delete(TB_NAME, "_id="+cur.getInt(0),null);
        requery();
    }