关于android 数据库SQLite的使用日记

自己也是第一次使用，中途遇到很多难题，总算努力还是会有收获，自己代码有很多不足的地方希望大神指出来一起学习，加油奥利给，话不多说贴代码

第一步，onCreate建立数据库

public  class DBHelperop  extends SQLiteOpenHelper {    // 数据库文件名    public static final String DB_NAME = "two.db";    // 数据库版本号    public static final int DB_VERSION = 1;    public DBHelperop(Context context) {        super(context, DB_NAME, null, DB_VERSION);    }    @Override    public void onCreate(SQLiteDatabase db) {        db.execSQL("CREATE TABLE  practic(id INTEGER PRIMARY KEY AUTOINCREMENT," +                             " num VARCHAR,newratio VARCHAR,numratio VARCHAR,total VARCHAR,str_time VARCHAR)");    }    @Override    public void onUpgrade(SQLiteDatabase db, int i, int i1) {    }}

第二步，我建了一个实体类接收数据，代码没贴完

public class DbInfor {    private int id;    private String num;    private double newratio;    private double numratio;    private double total;    private String str_time;    public DbInfor(){}    public DbInfor(String num, double newratio, double numratio, double total, String str_time) {        this.num = num;        this.newratio = newratio;        this.numratio = numratio;        this.total = total;        this.str_time = str_time;    }    public int getId() {        return id;    }    public void setId(int id) {        this.id = id;    }    public String getNum() {        return num;    }

第三步，建了一个管理数据库的类，我只做了两个查询和一个插入

public class DBManager {    private DBHelperop helper;   private SQLiteDatabase db;    public DBManager(Context context){        helper = new DBHelperop(context);             db = helper.getWritableDatabase();          }    public void add(List persons){                 db.beginTransaction();                try{                         for (DbInfor p:persons){                             db.execSQL("INSERT INTO practic (num,newratio,numratio,total,str_time)VALUES(?,?,?,?,?)",                                         //select * from role order by role_id desc limit 0,1;                                             new Object[]{p.getNum(),p.getNewratio(),p.getNumratio(),p.getTotal(),p.getStr_time()});                             }                        db.setTransactionSuccessful();                     }catch(Exception e){                        e.printStackTrace();                     }finally {                         db.endTransaction();                    }             }    public List findAllDbInfor(int a){                List dbinfoe = new ArrayList<>();                //"select * from practic order by id desc limit "+a+",2;"              Cursor c = db.rawQuery("select * from practic order by id desc limit "+a+",6", null);               while(c.moveToNext()){                   DbInfor p = new DbInfor();                         p.setId(c.getInt(c.getColumnIndex("id")));                        p.setNum(c.getString(c.getColumnIndex("num")));                         p.setNewratio(c.getDouble(c.getColumnIndex("newratio")));                        p.setNumratio(c.getDouble(c.getColumnIndex("numratio")));                   p.setTotal(c.getDouble(c.getColumnIndex("total")));                   p.setStr_time(c.getString(c.getColumnIndex("str_time")));                   dbinfoe.add(p);                    }                c.close();                return dbinfoe;             }    public DbInfor findDbInfor(){        DbInfor p = null;        Cursor c = db.rawQuery("select * from practic order by id desc limit 0,1", null);        while(c.moveToNext()){             p = new DbInfor();            p.setId(c.getInt(c.getColumnIndex("id")));            p.setNum(c.getString(c.getColumnIndex("num")));            p.setNewratio(c.getDouble(c.getColumnIndex("newratio")));            p.setNumratio(c.getDouble(c.getColumnIndex("numratio")));            p.setTotal(c.getDouble(c.getColumnIndex("total")));            p.setStr_time(c.getString(c.getColumnIndex("str_time")));        }        c.close();        return p;

第三步，一个输入数据的类，带一个查询，

public class MainActivity extends Activity{    private DBManager dm;    private EditText shuru;    private TextView shuchu;    private  int a = 100;    private  double newratio ;    private  double numratio ;    private double total;    private Button btConform;    private TextView cahkan;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        shuru = findViewById(R.id.et_etnum);        shuchu = findViewById(R.id.la_view2);        cahkan= findViewById(R.id.cahkan);        btConform = findViewById(R.id.bt_conform);        dm = new DBManager(this);        btConform.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                insertData();            }        });        cahkan.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                startActivity(new Intent(MainActivity.this,DetialActivity.class));            }        });    }        public void insertData(){            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm E");            Date date = new Date(System.currentTimeMillis());            String time = sdf.format(date);//获取系统时间            String shurunum = shuru.getText().toString();            DbInfor dbInform= dm.findDbInfor();//查询最后一个数据            newratio = Double.valueOf(shurunum)/(double)a;            if (dbInform==null){                numratio = Double.valueOf(shurunum)+0/(double)a;                total =Double.valueOf(shurunum)+0;            }else {                numratio = (Double.valueOf(shurunum)+dbInform.getTotal())/(double)a;                total =Double.valueOf(shurunum)+dbInform.getTotal();            }            List persons = new ArrayList<>();            DbInfor p1 = new DbInfor(shurunum,newratio,numratio,total,time);//插入获取的数据            persons.add(p1);            dm.add(persons);            findDb();    }    public  void findDb(){        //输出方法       DbInfor dbInfor= dm.findDbInfor();        if (dbInfor.getNumratio()==0){            shuchu.setText(0+"%");        }        DecimalFormat df=new DecimalFormat(".##");        double d=dbInfor.getNumratio()*100;        String st=df.format(d);        shuchu.setText(st+"%");    }}

第五步，查询所有数据并显示

public class DetialActivity extends AppCompatActivity implements XListView.IXListViewListener{    private TextView title,detail,time;    private ListRooAdapter listAdapter;    private XListView lvContent;    private DBManager dm;    private int a=0;       @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_detial);        title= findViewById(R.id.news_tvtitle);        detail= findViewById(R.id.news_tvdetail);        title= findViewById(R.id.news_tvtime);        dm = new DBManager(this);        listAdapter= new ListRooAdapter(this);        lvContent =findViewById(R.id.lvcent);        lvContent.setXListViewListener(this);        lvContent.setPullRefreshEnable(true);        lvContent.setPullLoadEnable(true);        lvContent.hideFoot();        lvContent.setAdapter(listAdapter);        love();    }     public  void  love(){         onComplete();         List datas = dm.findAllDbInfor(a);         if (datas.size()<0){             Toast.makeText(this, "暂时还没有记录呢", Toast.LENGTH_SHORT).show();         }         if(datas.size() < 5){             lvContent.hideFoot();//根据数据显示长度的，显示加载按钮         }else{             lvContent.showFoot();         }         // lvContent.showFoot();         if(a == 0) {             listAdapter.setDatas(datas);         }else{             listAdapter.addDatas(datas);         }         if(datas.size()>0){             a+=6;         }     }    @Override    public void onRefresh() {//下拉刷新        a=0;        love();    }    @Override    public void onLoadMore() {        love();//点击加载    }    public void onComplete(){        lvContent.stopLoadMore();        lvContent.stopRefresh();    }}

其他代码我就不贴了，每个人用数据库有自己的用法如需要联系我
最后效果因为原因没上传，有些方法参考了该作者链接为
2021年1月6日周三凌晨12：53

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