Android SQLite数据库未创建

Question

我是android新手，想为我的android应用程序设计数据库，但我无法做到这一点。 我已尽一切努力查找错误，但找不到任何错误，仍然无法创建数据库。 请有人帮助我，在此先感谢。

代码如下：

型号类别：

package com.example.health;

public class Daily {
private int _id;
private String _tips;

public Daily(){
}

public Daily(int id, String tips){
    this._id=id;
    this._tips=tips;
}
public Daily(String tips){
    this._tips=tips;
}
public void setID(int id) {
    this._id = id;
}
public void setTips(String tips){
    this._tips=tips;
}
public int getID() {
    return this._id;
}
public String getTips(){
    return this._tips;
}
  }

数据库处理程序：

 package com.example.health;

import java.util.ArrayList;
import java.util.List;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;


public class MyDBHandler extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "healthDB.db";
private static final String TABLE_DAILY = "daily";

public static final String COLUMN_ID = "_id";
public static final String COLUMN_TIPS = "tips";

public MyDBHandler(Context context, String name, 
        CursorFactory factory, int version) {
    super(context, DATABASE_NAME, factory, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_DAILY_TABLE = "CREATE TABLE " + TABLE_DAILY + "(" + COLUMN_ID + " INTEGER PRIMARY KEY," + COLUMN_TIPS + " TEXT " + ")";
      db.execSQL(CREATE_DAILY_TABLE);

      }

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_DAILY);
      onCreate(db);
}
public void addDaily(Daily daily) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(COLUMN_TIPS, daily.getTips());
    db.insert(TABLE_DAILY, null, values);
    db.close();
}
 public List<Daily> getAllDailys(){
        List <Daily> dailyList=new ArrayList<Daily>();

        // Select All Query
        String selectQuery="SELECT * FROM " + TABLE_DAILY;

        SQLiteDatabase db=this.getReadableDatabase();
        Cursor c=db.rawQuery(selectQuery, null);

        // looping through all rows and adding to the list
        if(c.moveToFirst()){
            do{
                Daily daily=new Daily();
                daily.setID(Integer.parseInt(c.getString(0)));
                daily.setTips(c.getString(1));


                // Adding user to the list
                dailyList.add(daily);
            }while(c.moveToNext());
        }
        c.close();
        return dailyList;
}}

Answer 1

请注意， 仅在对数据库本身执行某些操作之后才创建数据库 。 即，仅创建SQLiteOpenHelper类将不会在设备中创建数据库， 直到您对数据库执行某些读/写操作为止 。

[编辑1] ，直到您执行以下操作：

MyDBHandler db = new MyDBHandler(....);
db.addDaily(daily);

该数据库将不会被创建。

[编辑2]您可能还想更改MyDBHandler类的构造函数：

public MyDBHandler(Context contex) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

[注意]我假设您没有任何错误/异常。

Answer 2

您的DbClass

package com.example.demo;
import java.util.ArrayList;
import java.util.List;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;


public class MyDBHandler extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "healthDB.db";
private static final String TABLE_DAILY = "daily";

public static final String COLUMN_ID = "_id";
public static final String COLUMN_TIPS = "tips";

static MyDBHandler mDbHelper;

private MyDBHandler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

public static synchronized MyDBHandler getInstance(Context context) {
    if (mDbHelper == null) {
        mDbHelper = new MyDBHandler(context);
    }
    return mDbHelper;
}

@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_DAILY_TABLE = "CREATE TABLE " + TABLE_DAILY + "(" + COLUMN_ID + " INTEGER PRIMARY KEY," + COLUMN_TIPS + " TEXT " + ")";
      db.execSQL(CREATE_DAILY_TABLE);

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_DAILY);
      onCreate(db);
}
public void addDaily(Daily daily) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(COLUMN_TIPS, daily.getTips());
    db.insert(TABLE_DAILY, null, values);
    db.close();
}
 public List<Daily> getAllDailys(){
        List <Daily> dailyList=new ArrayList<Daily>();

        // Select All Query
        String selectQuery="SELECT * FROM " + TABLE_DAILY;

        SQLiteDatabase db=this.getReadableDatabase();
        Cursor c=db.rawQuery(selectQuery, null);

        // looping through all rows and adding to the list
        if(c.moveToFirst()){
            do{
                Daily daily=new Daily();
                daily.setID(Integer.parseInt(c.getString(0)));
                daily.setTips(c.getString(1));


                // Adding user to the list
                dailyList.add(daily);
            }while(c.moveToNext());
        }
        c.close();
        return dailyList;
}}

您可以像这样添加数据

MyDBHandler db = MyDBHandler.getInstance(getApplicationContext());
Daily daily = new Daily();
daily.setID(1);
daily.setTips("hello");
db.addDaily(daily);

我已经测试过了 它工作正常。