Android记事本项目1-创建数据库

对于Android记事本，首先最需要的当然 就是数据库了。

在开发本项目的最开始时，应该先写一个数据库类NoteDB

package com.kfchen.hellonotes2;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;/** * Created by 猎隼 on 2017/2/27. */public class NoteDB 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 NoteDB(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 sqLiteDatabase, int i, int i1) {    }}然后在主函数中将数据库实例化，并且写一个添加数据的的函数测试是否数据库可用
package com.kfchen.hellonotes2;import android.content.ContentValues;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import java.text.SimpleDateFormat;import java.util.Date;public class MainActivity extends AppCompatActivity {    private NoteDB noteDB;    private SQLiteDatabase dbWriter;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        noteDB = new NoteDB(this); //实例化数据库        dbWriter = noteDB.getWritableDatabase();   //获取数据库写入权限        addDB();    }    //向数据库中添加数据    public void addDB(){        ContentValues cv = new ContentValues();        cv.put(NoteDB.CONTENT,"Hello");        cv.put(NoteDB.TIME,getTime());        dbWriter.insert(NoteDB.TABLE_NAME,null,cv); //cv则为插入数据表的具体内容    }    //获取设备当前的时间，并且以自定义的格式呈现       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);        return str;       };}