Android SQLiteDatabase 如何灌注初始数据?

Question

创建了一个继承SQLiteOpenHelper的类，在其中的：onCreate方法中创建数据表结构，同时我想再插入一条默认的数据（要求是：像onCreate一样，只要数据表已经存在，就不要再次重复插入默认数据）研究了半天，有个onOpen方法，但好像每次打开数据库它都会执行，肿么办呢？
下面把代码贴出来吧

package Dal;

import android.annotation.SuppressLint;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.DatabaseErrorHandler;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import java.time.LocalDateTime;

import Model.M;
import Model.Mt_Message;
import Model.Mt_settings;

public class DbHelper extends SQLiteOpenHelper {
    private static final String DBNAME = "lkfscreendb.db";//数据库名字
    private static final String T_settings = "T_settings";//表名
    private static final String T_Message = "T_Message";//表名
    private static final int VERSION = 1;//数据库版本号,一般以 1 开始
    private SQLiteDatabase mReadLink;//读链接 因为读写时 数据库的锁 不一样
    private SQLiteDatabase mWriteLink;// 写链接

    private static DbHelper mInstance;
    /**
     * 单利模式得到数据库操作类的唯一实例
     * 建议在应用页面的 onStart()调用
     * @param p_context
     * @return
     */
    public static DbHelper getInstance(Context p_context){
        if (mInstance == null){
            mInstance = new DbHelper(p_context);
        }
        return mInstance;
    }
    public DbHelper(@Nullable Context context) {
        super(context, DBNAME, null, VERSION);
    }
    /**
     * 打开可读数据库链接 （只有查询用可读链接）
     *  建议在Activity应用页面的 onStart()统一调用
     *  在其他类中 例如MyApplication中 打开链接与关闭链接成对出现！
     * @return
     */
    public SQLiteDatabase openReadLink(){
        if (this.mReadLink == null || !this.mReadLink.isOpen()){
            this.mReadLink = mInstance.getReadableDatabase();
        }
        return this.mReadLink;
    }

    /**
     * 打开可写数据库链接 （增删改 都用可写链接）
     * 建议在应Activity用页面的 onStart()统一调用
     * 在其他类中 例如MyApplication中 打开链接与关闭链接成对出现！
     * @return
     */
    public SQLiteDatabase openWriteLink(){
        if (this.mWriteLink == null || !this.mWriteLink.isOpen()){
            this.mWriteLink = mInstance.getWritableDatabase();
        }
        return this.mWriteLink;
    }
    /**
     * 关闭数据库链接 （可读可写链接都关闭）
     * 建议在Activity应用页面的  onStop()方法调用
     * 如果该页面是主页面 放在 onDestroy()方法中调用
     *
     * 在其他类中 例如MyApplication中 打开链接与关闭链接成对出现！
     */
    public void closeLink(){
        if (this.mReadLink != null && this.mReadLink.isOpen()) {
            this.mReadLink.close();
            this.mReadLink = null;
        }
        if (this.mWriteLink != null && this.mWriteLink.isOpen()) {
            this.mWriteLink.close();
            this.mWriteLink = null;
        }
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        StringBuffer lSbSql1 = new StringBuffer();
        lSbSql1.append("CREATE TABLE IF NOT EXISTS "+T_settings+" (");
        lSbSql1.append("Id INTEGER PRIMARY KEY AUTOINCREMENT, TextOrientation TEXT (50)  NOT NULL, Speed REAL NOT NULL,TextSize INTEGER NOT NULL,");
        lSbSql1.append("Font TEXT (50)  NOT NULL, TextColor TEXT (10) NOT NULL,Background TEXT (50) NOT NULL,ColorMatching TEXT (100) NOT NULL,");
        lSbSql1.append(" IsCurrent INTEGER NOT NULL);");
        db.execSQL(lSbSql1.toString());
        StringBuffer lSbSql2 = new StringBuffer();
        lSbSql2.append("CREATE TABLE IF NOT EXISTS "+T_Message+" (");
        lSbSql2.append(" Id INTEGER PRIMARY KEY AUTOINCREMENT, DataMessage TEXT (1000), IsCurrent INTEGER NOT NULL);");
        db.execSQL(lSbSql2.toString());
        try{
            addInitDefaultValues();
        }catch(Exception e){
            Log.i("LKFTAG", "Exception: "+e.getMessage());
        }
//        Exception: getDatabase called recursively

    }

    @Override
    public void onOpen(SQLiteDatabase db) {
        super.onOpen(db);
         Log.d("LKFTAG", "DbHelper_onOpen:"+ java.time.LocalTime.now());
    }

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



    /**
     * 向两个表里出入初始化数据 （一次性插入多条数据 这里使用了事务机制）
     * @return  true为成功
     */
    public boolean addInitDefaultValues(){
        boolean lIsSuccess = false;
        try {
            this.openWriteLink().beginTransaction();

            ContentValues lCvT_settings = new ContentValues();
            lCvT_settings.put(M.TextOrientation,"rbtn_horizontal");
            lCvT_settings.put(M.Speed,0);
            lCvT_settings.put(M.TextSize,72);
            lCvT_settings.put(M.Font,"simfang.ttf");
            lCvT_settings.put(M.TextColor,"#ffffff");
            lCvT_settings.put(M.Background,"#000000");
            lCvT_settings.put(M.ColorMatching,"#ffffff|#000000");
            lCvT_settings.put(M.IsCurrent,1);
            this.mWriteLink.insert(T_settings,null,lCvT_settings);

            ContentValues lCvT_Message = new ContentValues();
            lCvT_Message.put(M.DataMessage,"");
            lCvT_Message.put(M.IsCurrent,1);
            this.openWriteLink().insert(T_Message,null,lCvT_Message);


            this.mWriteLink.setTransactionSuccessful();
            lIsSuccess = true;
        }catch (Exception ex){ex.printStackTrace();}
        finally {
            this.openWriteLink().endTransaction();
        }
        return lIsSuccess;
    }

    @SuppressLint("Range")
    public Mt_settings queryTsettingByIsCurrent(){
        Mt_settings lTmodel = new Mt_settings();
        Cursor lCursor = this.mReadLink.query(T_settings,
                new String[]{"Id","TextOrientation","Speed","TextSize","Font","TextColor","Background","ColorMatching"},
                "IsCurrent = @IsCurrent",new String[]{"1"},
                null,null,null);
        while (lCursor.moveToNext()){
            lTmodel.setId(lCursor.getInt(lCursor.getColumnIndex("Id")));
            lTmodel.setTextOrientation(lCursor.getString(lCursor.getColumnIndex("TextOrientation")));
            lTmodel.setSpeed(lCursor.getFloat(lCursor.getColumnIndex("Speed")));
            lTmodel.setTextSize(lCursor.getInt(lCursor.getColumnIndex(M.TextSize)));
            lTmodel.setFont(lCursor.getString(lCursor.getColumnIndex(M.Font)));
            lTmodel.setTextColor(lCursor.getString(lCursor.getColumnIndex(M.TextColor)));
            lTmodel.setBackground(lCursor.getString(lCursor.getColumnIndex(M.Background)));
            lTmodel.setColorMatching(lCursor.getString(lCursor.getColumnIndex(M.ColorMatching)));
        }
        return lTmodel;
    }
    @SuppressLint("Range")
    public Mt_Message queryTmessageByIsCurrent(){
        Mt_Message lTmodel = new Mt_Message();
        Cursor lCursor = this.mReadLink.query(T_Message,
                new String[]{"Id","DataMessage"},
                "IsCurrent = @IsCurrent",new String[]{"1"},
                null,null,null);
        while (lCursor.moveToNext()){
            lTmodel.setId(lCursor.getInt(lCursor.getColumnIndex("Id")));
            lTmodel.setDataMessage(lCursor.getString(lCursor.getColumnIndex(M.DataMessage)));
        }
        return lTmodel;
    }

    public void UpdateDataMessage(String pValue) {
        ContentValues lContenValues = new ContentValues();
        lContenValues.put(M.DataMessage,pValue);
        this.mWriteLink.update(T_Message,lContenValues,
                "IsCurrent = @IsCurrent",new String[]{"1"});
    }
    //  l_ContentValues.put("Address",pUser.getAddress()); 不需要更新的值不要给值，否则将更新为null
    public long updateTextOrientation(String pTextOrientation){
        ContentValues l_ContentValues = new ContentValues();
        l_ContentValues.put(M.TextOrientation,pTextOrientation);
        return this.mWriteLink.update(T_settings,l_ContentValues,
                "IsCurrent = @IsCurrent",new String[]{"1"});
    }
    public void UpdateBackground(String pResouceID) {
        ContentValues lContenValues = new ContentValues();
        lContenValues.put(M.Background,pResouceID);
        this.mWriteLink.update(T_settings,lContenValues,
                "IsCurrent = @IsCurrent",new String[]{"1"});
    }

    public void UpdateTextColor(String pTag) {
        ContentValues lContenValues = new ContentValues();
        lContenValues.put(M.TextColor,pTag);
        this.mWriteLink.update(T_settings,lContenValues,
                "IsCurrent = @IsCurrent",new String[]{"1"});
    }



    public void UpdateTextSize(String pTextSize) {
        ContentValues lContenValues = new ContentValues();
        lContenValues.put(M.TextSize,pTextSize);
        this.mWriteLink.update(T_settings,lContenValues,
                "IsCurrent = @IsCurrent",new String[]{"1"});
    }

    public void UpdateSpeed(String pSpeed) {
        ContentValues lContenValues = new ContentValues();
        lContenValues.put(M.Speed,pSpeed);
        this.mWriteLink.update(T_settings,lContenValues,
                "IsCurrent = @IsCurrent",new String[]{"1"});
    }

    public void UpdateFont(String pFont) {
        ContentValues lContenValues = new ContentValues();
        lContenValues.put(M.Font,pFont);
        this.mWriteLink.update(T_settings,lContenValues,
                "IsCurrent = @IsCurrent",new String[]{"1"});
    }
}

Answer 1

• 你看下这篇博客吧, 应该有用👉 ：使用SQLite数据库进行创建表时没有走onCreate()方法
• 除此之外, 这篇博客: 安卓之数据库（SQLite）中的 1.编写类继承SQLiteOpenHelper，覆写onCreate方法和onUpgrade方法 部分也许能够解决你的问题, 你可以仔细阅读以下内容或跳转源博客中阅读:
  

• package com.example.yogi.courseapp;
  
  import android.content.Context;
  import android.database.sqlite.SQLiteDatabase;
  import android.database.sqlite.SQLiteOpenHelper;
  
  public class CourseData extends SQLiteOpenHelper {
      private static final String db_name = "CourseDatas";//自定义的数据库名；
      private static final int version = 2;//版本号,增加则会执行onUpgrade方法?
  
      public CourseData(Context context) {
          super(context, db_name, null, version);
  
      }
  
      // 该方法会自动调用，首先系统会检查该程序中是否存在数据库名为‘CoursDatas’的数据库
      // 如果存在则不会执行该方法，如果不存在则会执行该方法。
      @Override
      public void onCreate(SQLiteDatabase db) {
          String  sql ="create table courses(" +
                  "id Integer primary key autoincrement," +     //id自增,只支持integer不支持int
                  "coursename varchar(30)," +
                  "teacher varchar(20)," +
                  "time varchar(50)," +
                  "classroom varchar(30)" +
                  ")";
          db.execSQL(sql);
      }
  
      //数据库版本更新时执行该方法,如果表已存在则先删除再调用onCreate重新创建
      @Override
      public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
          db.execSQL("drop table if exists courses");
          onCreate(db);
      }
  }