创建Sqlite数据库(二)

先创建一个数据库表,然后在主activity中执行删除更新操作

public class MainActivity extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Mysqlite mysqlite = new Mysqlite(this);
        SQLiteDatabase sqLiteDatabase = mysqlite.getWritableDatabase();

        ContentValues contentValues = new ContentValues();
        contentValues.put("id", 0);
        contentValues.put("name", "张三");
        sqLiteDatabase.insert("student", null, contentValues);
        System.out.println("插入数据");

        Cursor cursor = sqLiteDatabase.query("student", new String[]{"id", "name"}, "id=?", new String[]{"0"}, null,
                null, null);
        while (cursor.moveToNext()) {
            String id = cursor.getString(cursor.getColumnIndex("id"));
            String name = cursor.getString(cursor.getColumnIndex("name"));
            System.out.println(id + "  " + name);
        }

            ContentValues contentValues1 = new ContentValues();
            contentValues1.put("name", "李四");
            sqLiteDatabase.update("student", contentValues1, "id=?", new String[]{"0"});//?是占位符,后面String
        //数组的元素0填补前面的占位符?,也就是id=0,whereClause(where字句)只是一个限制条件
            System.out.println("更新数据");

        sqLiteDatabase.delete("student", "id=?", new String[]{"0"});
        System.out.println("删除数据");

        deleteDatabase("student");
        System.out.println("删除数据库");

        sqLiteDatabase.close();
        }
    }

上面是主Activity,不要重复创建sqliteDatabase,不然内部无法同步

public class Mysqlite extends SQLiteOpenHelper {
    SQLiteDatabase readableDatabase;
    public Mysqlite(Context context) {
        super(context, "student", null, 2);
        readableDatabase = getWritableDatabase();//创建数据库不需要什么权限,但是这行代码一定要写
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        db.execSQL("create table student (id integer,name varchar)");
        System.out.println("创建");
    }

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

    }
}

上面是创建数据库//重要的事情说三遍