Android数据存储基础：

  // 权限回调   
@Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults)
    {
        if (requestCode == MY_PERMISSIONS_REQUEST_CALL_PHONE)
        {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED)
            {
                try {
                    writeSdOut();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } else
            {
                // Permission Denied
                Toast.makeText(MainActivity.this, "Permission Denied", Toast.LENGTH_SHORT).show();
            }
            return;
        }
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    }
//  写入SD卡内容
  public static int MY_PERMISSIONS_REQUEST_CALL_PHONE=100;
    public void  writeSDW(View view)  {
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED)
        {
            ActivityCompat.requestPermissions(MainActivity.this,
                    new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},MY_PERMISSIONS_REQUEST_CALL_PHONE);
        } else
        {
            try {
                writeSdOut();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
 public void writeSdOut() throws IOException {
        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
            // /storage/emulated/0
            String sdPath = Environment.getExternalStorageDirectory().getAbsolutePath();
            Log.e("sdPath:",sdPath);
            //   /storage/emulated/0
            File file = new File(sdPath+"/atguigu");
            if(!file.exists()) {
                file.mkdirs();//创建文件夹
            }
            String filePath = sdPath+"/atguigu/"+"a.txt";
            FileOutputStream fos = new FileOutputStream(filePath);
            //4. 写数据
            fos.write("sd卡外部存储".getBytes("utf-8"));
            fos.close();
        }
    }
//  读取SD卡内容
 public void  readSDW(View view) throws IOException {
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.CALL_PHONE)
                != PackageManager.PERMISSION_GRANTED) {
            String sdPath = Environment.getExternalStorageDirectory().getAbsolutePath();
            //   /storage/emulated/0
            File file = new File(sdPath+"/atguigu");
            String filePath = sdPath+"/atguigu/"+"a.txt";
            Log.e("sdPath:",sdPath);
            FileInputStream fis = new FileInputStream(filePath);
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            int len = -1;
            while((len=fis.read(buffer))!=-1) {
                baos.write(buffer, 0, len);
            }
            String content = baos.toString();
            Log.e("readSDW-->content:",content);
            fis.close();
        }
    }

package com.example.myapplication;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBHelper extends SQLiteOpenHelper {
	public DBHelper(Context context,int version) {
		super(context, "atguigu.db", null, version);
	}
	
	@Override
	public void onCreate(SQLiteDatabase db) {
		Log.e("TAG", "DBHelper onCreate()");
		//建表
		String sql = "create table person(_id integer primary key autoincrement, name varchar,age int)";
		db.execSQL(sql);
		//插入一些初始化数据
		db.execSQL("insert into person (name, age) values ('Tom1', 11)");
		db.execSQL("insert into person (name, age) values ('Tom2', 12)");
		db.execSQL("insert into person (name, age) values ('Tom3', 13)");
	}
	//当传入的版本号大于数据库的版本号时调用
	// 用户版本升级
	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
		Log.e("TAG", "DBHelper onUpgrade()-->"+"oldVersion:"+oldVersion + "newVersion:"+newVersion);
	}
    // 还有版本下降的时候调用的方法onDowngrade
}

   
    public void  creatTable(View view){
     DBHelper dbHelper=new DBHelper(this,1);
        // 创建数据源库
    //    dbHelper.getWritableDatabase();  //本地空间满了如果，继续插入没有反应
        // 连接数据库,得到连接
      SQLiteDatabase sqLiteDatabase=dbHelper.getReadableDatabase();  // 本地空间满了如果，继续插入抛异常
    }

   public void updateTable(View view){
        DBHelper dbHelper=new DBHelper(this,2);
        // 连接数据库才会更新
        // 回调 onUpgrade 回调方法，比如更新一些字段
        SQLiteDatabase sqLiteDatabase=dbHelper.getReadableDatabase();
    }

public void insertFun(View view){
        DBHelper dbHelper=new DBHelper(this,2);
        SQLiteDatabase sqLiteDatabase=dbHelper.getReadableDatabase();
        //insert into person (name, age) values ('Tom1', 11)
        ContentValues contentValues=new ContentValues();
        contentValues.put("name","denganzhi");
        contentValues.put("age",25);
       long id= sqLiteDatabase.insert("person",null,contentValues);
        sqLiteDatabase.close();
        Toast.makeText(MainActivity.this,"longid:"+id,Toast.LENGTH_SHORT).show();
    }
    public void updateFun(View view){
        DBHelper dbHelper=new DBHelper(this,2);
        SQLiteDatabase sqLiteDatabase=dbHelper.getReadableDatabase();
        ContentValues contentValues=new ContentValues();
        contentValues.put("age","300000");
        int updateCount=sqLiteDatabase.update("person",contentValues,"_id=?",new String[]{"5"});
        sqLiteDatabase.close();
        Toast.makeText(MainActivity.this,"updateCount:"+updateCount,Toast.LENGTH_SHORT).show();
    }
    public void deleteFun(View view){
        DBHelper dbHelper=new DBHelper(this,2);
        SQLiteDatabase sqLiteDatabase=dbHelper.getReadableDatabase();
        int deleteId= sqLiteDatabase.delete("person","_id=5",null);
        sqLiteDatabase.close();
        Toast.makeText(MainActivity.this,"deleteId:"+deleteId,Toast.LENGTH_SHORT).show();
    }
    public void selectFun(View view){
        DBHelper dbHelper=new DBHelper(this,2);
        SQLiteDatabase sqLiteDatabase=dbHelper.getReadableDatabase();
   // select * from person
        //query(String table, String[] columns, String selection,
       // String[] selectionArgs, String groupBy, String having,
         //       String orderBy)
        Cursor cursor =  sqLiteDatabase.query("person",null,"_id=?",new String[]{"3"},null,null,null);
        int count =cursor.getCount();  // 得到上面匹配的总数
        while(cursor.moveToNext()){
            int id= cursor.getInt(0);
            String name =cursor.getString(1);
            int age= cursor.getInt(cursor.getColumnIndex("age")); //如果记得名字了可以这样
            Log.e("denganzhi","count:"+count + " id:"+id +" name:"+ name + " age:"+ age);
        }
        cursor.close();
        sqLiteDatabase.close();
    }

    public void operatorTransiction(View view){
        DBHelper dbHelper=new DBHelper(this,2);
        SQLiteDatabase sqLiteDatabase=dbHelper.getReadableDatabase();
        // 1.开启事务, 不会自动保存提交了
        sqLiteDatabase.beginTransaction();
        ContentValues contentValues1=new ContentValues();
        contentValues1.put("age","300000");
        int updateCount1=sqLiteDatabase.update("person",contentValues1,"_id=?",new String[]{"1"});
        int j=1/0;
        contentValues1=new ContentValues();
        contentValues1.put("age","200000");
        updateCount1=sqLiteDatabase.update("person",contentValues1,"_id=?",new String[]{"2"});
        //2. 设置事务在全局
        sqLiteDatabase.setTransactionSuccessful();
        // 3. 结束事务
        sqLiteDatabase.endTransaction();
        sqLiteDatabase.close();
    }