Anroid-Sqlite 数据存储、查询_android sqlite查询

m//功能描述：
//实现数据的插入、查询和根据ID查询
//2023.6.23
//Liyumin

MainActivity:

public class MainActivity extends AppCompatActivity {
    //将需要用到的类单独拉出来
    Button addBtn;
    Button queryallButton;
    Button queryoneButton;
    EditText nameField;
    EditText ageField;
    EditText highFiled;
    TextView resultField;
    TextView idField;
 
    DbAdapter dbAdapter;//声明
 
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //实例化
        dbAdapter = new DbAdapter(this);
        dbAdapter.open(); //链接数据库
 
 
        //1.组件相关配置
        addBtn          =  findViewById(R.id.addbutton);
        nameField       =  findViewById(R.id.namefileld);
        ageField        =  findViewById(R.id.agefield);
        highFiled       =  findViewById(R.id.highfield);
        queryallButton  =  findViewById(R.id.queryallButton);
        queryoneButton  =  findViewById(R.id.queryone);
        idField         =  findViewById(R.id.idField);
        resultField     = findViewById(R.id.result);
        //2.保存按键中断
        addBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //拿到数据
                String name = nameField.getText().toString();
                int age = Integer.parseInt(ageField.getText().toString());
                float high = Float.parseFloat(highFiled.getText().toString());
 
                Person p = new Person(name,age,high);
                dbAdapter.insert(p);
            }
        });
        //3.查询按键中断
        queryallButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String result = "";
 
                Person[] ps = dbAdapter.getALLData();
                for(Person p:ps)
                {
                    result += p.name + "," + p.age + "," + p.high + "\n";
                }
                resultField.setText(result);
 
            }
        });
        //4.根据ID查询
        queryoneButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String result = "";
                int id = Integer.parseInt(idField.getText().toString());
                Person p = dbAdapter.queryById(id);
                result += p.name + "," + p.age + "," + p.high + "\n";
                resultField.setText(result);
 
 
            }
        });
 
 
 
    }
}

DbAdapter：

//通过这个文件与Sqlite打交道
public class DbAdapter {
    SQLiteDatabase db;
    Context   context;
 
    DBOpenHelper dBopenhelper;
    //创建一个名称为people的数据库
    public static  final  String mysql = "people";
 
    public DbAdapter(Context context) {
        this.context = context;
    }
    //打开数据库
    public void open(){
        dBopenhelper = new DBOpenHelper(
                context,mysql,null,1);
        //真正的实例化db
        db = dBopenhelper.getReadableDatabase();
        try {
            db = dBopenhelper.getWritableDatabase();
        } catch (SQLException e) {
            db  = dBopenhelper.getReadableDatabase();
        }
    }
    //关闭数据库
    public void close(){
        if (db!= null)
        {
            db.close();
            db = null;
        }
    }
    //添加数据到表格------！！！！！！重点看看！！！！！！！！！！！！
    public void insert(Person p) {
        ContentValues cv = new ContentValues();
        cv.put("name",p.name);
        cv.put("age",p.age);
        cv.put("high",p.high);
        db.insert(mysql,null,cv);
 
    }
 
    //读取数据用到------！！！！！！重点看看！！！！！！！！！！！！
    public Person[] getALLData() {
        //cursor为指针
        Cursor cursor = db.query(mysql,new String[]{"_id","name","age","high"},
                                          null,null,null,null,null);
        return convertToPerson(cursor);
    }
 
    @SuppressLint("Range")
    //------！！！！！！重点看看！！！！！！！！！！！！
    //这个函数是用来处理从Sqlite中获取的数据
    private Person[] convertToPerson(Cursor cursor) {
        int rowCount = cursor.getCount();
        if(rowCount == 0 || !cursor.moveToFirst())
        {
            return null;
        }
 
        Person[] ps = new Person[rowCount];
        for(int i=0;i<rowCount;i++)
        {
            ps[i] = new Person();
            //重点掌握！！！！！！！！！！！！！！！！！！！！！！！！！！！
            ps[i].name = cursor.getString(cursor.getColumnIndex("name"));
            ps[i].age = cursor.getInt(cursor.getColumnIndex("age"));
            ps[i].high = cursor.getFloat(cursor.getColumnIndex("high"));
            cursor.moveToNext();
 
        }
        return ps;
    }
 
    public Person queryById(int id) {
        //重点掌握！！！！！！！！！！！！！！！！！！！！！！！！！！！
        Cursor cursor = db.query(mysql,new String[]{"_id","name","age","high"},
                "_id="+id,null,null,null,null);
        Person[] ps = convertToPerson(cursor);
        if(ps != null)
        {
            return ps[0];
        }
        return null;
    }
 
    private class DBOpenHelper extends SQLiteOpenHelper {
        //构造方法
        public DBOpenHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
            super(context, name, factory, version);
        }
        private  static  final  String DB_CREATE =
                "create table "+ mysql +"("+
                        "_id integer primary key autoincrement,"+
                        "name text,"+
                        "age integer,"+
                        "high float)";
        //重要
        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(DB_CREATE);//执行SQL代码
 
        }
 
        @Override
        public void onUpgrade(
                SQLiteDatabase sqLiteDatabase, int i, int i1) {
 
        }
    }
}

Person.class

//描述数据表的结构
public class Person {
    String name;
    int age;
    float high;
 
    public Person() {
 
    }
    //增加一个构造方法 -- 本质就是用来创建实例时进行赋值
    public Person(String name, int age, float high) {
        this.name = name;
        this.age = age;
        this.high = high;
    }
 
 
}