学习数据库遇到的问题。

ff_super 2019-05-27 08:40:08

小白刚学习数据库的基础知识，照视频做怎么打开db文件，没有数据，一条都没有，请大神们解答下，谢谢。

import android.content.Context;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteOpenHelper;



public class NotesDB extends SQLiteOpenHelper {



    public static final String TABLE_NAME = "notes";

    public static final String CONTENT = "content";

    public static final String ID = "_id";

    public static final String TIME = "time";



    public NotesDB(Context context) {

        super(context, "notes", null, 1);

    }



    @Override

    public void onCreate(SQLiteDatabase db) {

        db.execSQL("CREATE TABLE " + TABLE_NAME + "(" + ID

                + " INTEGER PRIMARY KEY AUTOINCREMENT," + CONTENT

                + " TEXT NOT NULL," + TIME + " TEXT NOT NULL)");

    }



    @Override

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



    }

}

这是主activity



import android.Manifest;

import android.content.ContentValues;

import android.database.sqlite.SQLiteDatabase;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.TextView;

import android.widget.Toast;



import com.ysuper2009.note.R;

import com.ysuper2009.note.db.NotesDB;

import com.ysuper2009.note.util.YPermissionManager;



import java.text.SimpleDateFormat;

import java.util.Date;

import java.util.List;



import pub.devrel.easypermissions.AppSettingsDialog;

import pub.devrel.easypermissions.EasyPermissions;





public class MainActivity extends AppCompatActivity  {



    private String[] perms = {Manifest.permission.CAMERA, Manifest.permission.WRITE_EXTERNAL_STORAGE} ;

    private TextView tv;

    //数据库内容

    private NotesDB notesDB;

    private SQLiteDatabase dbWriter;



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        tv = (TextView)findViewById(R.id.tx);





        //YPermissionManager yPermissionManager = new YPermissionManager();

        //yPermissionManager.checkBasePermission(this, perms);



        notesDB = new NotesDB(this);

        dbWriter = notesDB.getWritableDatabase();

        add();



    }



    public void add(){

        ContentValues cv = new ContentValues();

        cv.put(NotesDB.CONTENT, "tongtong");

        cv.put(NotesDB.TIME, getTime());

        dbWriter.insert(NotesDB.TABLE_NAME, null, cv);



    }



    public String getTime(){

        SimpleDateFormat format = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");

        Date curDate = new Date();

        String str = format.format(curDate);

        tv.setText(str);

        return str;

    }



    /*

    @Override

    public void onRequestPermissionsResult(int requestCode,  String[] permissions,  int[] grantResults) {

        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        EasyPermissions.onRequestPermissionsResult(requestCode, permissions, grantResults);

    }



    @Override

    public void onPermissionsGranted(int requestCode,  List<String> perms) {

        Toast.makeText(this, "permission is ok,please use it", Toast.LENGTH_SHORT).show();

    }



    @Override

    public void onPermissionsDenied(int requestCode,  List<String> perms) {

        Toast.makeText(this, "permission fail", Toast.LENGTH_SHORT).show();

        if (EasyPermissions.somePermissionPermanentlyDenied(this, perms)) {

            new AppSettingsDialog.Builder(this).build().show();

            }

        }



    */



    }