我有一個現有的SQLite數據庫，但未能與我的應用程序一起使用

Question

我已經閱讀了幾個有關我的問題的教程，例如This和This沒有人告訴我整個過程。每個人都講述了DataBaseHelper類，但沒有人展示如何使用MainActivity實現。我們還應該使用什麼樣的光標來提取數據，並將這些數據保存在每一列的字符串中。

這裏是我的DataBaseHelper.java代碼，但它亙古不變的數據複製到我的應用程序。

import java.io.File; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.OutputStream; 
import android.content.Context; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.util.Log; 

public class DataBaseHelper extends SQLiteOpenHelper 
{ 
    private static String TAG = "DataBaseHelper"; // Tag just for the LogCat window 
    //destination path (location) of our database on device 
    private static String DB_PATH = ""; 
    private static String DB_NAME ="SBLdata.db";// Database name 
    private SQLiteDatabase mDataBase; 
    private final Context mContext; 

    public DataBaseHelper(Context context) 
    { 
     super(context, DB_NAME, null, 1);// 1? its Database Version 
     if(android.os.Build.VERSION.SDK_INT >= 17){ 
      DB_PATH = context.getApplicationInfo().dataDir + "/databases/"; 
     } 
     else 
     { 
      DB_PATH = "/data/data/" + context.getPackageName() + "/databases/"; 
     } 
     this.mContext = context; 
    } 

    public void createDataBase() throws IOException 
    { 
     //If database not exists copy it from the assets 

     boolean mDataBaseExist = checkDataBase(); 
     if(!mDataBaseExist) 
     { 
      this.getReadableDatabase(); 
      this.close(); 
      try 
      { 
       //Copy the database from assests 
       copyDataBase(); 
       //Log.e(TAG, "createDatabase database created"); 
      } 
      catch (IOException mIOException) 
      { 
       throw new Error("ErrorCopyingDataBase"); 
      } 
     } 
    } 
    //Check that the database exists here: /data/data/your package/databases/Da Name 
    private boolean checkDataBase() 
    { 
     File dbFile = new File(DB_PATH + DB_NAME); 
     Log.v("dbFile", dbFile + " "+ dbFile.exists()); 
     return dbFile.exists(); 
    } 

    //Copy the database from assets 
    private void copyDataBase() throws IOException 
    { 
     InputStream mInput = mContext.getAssets().open(DB_NAME); 
     String outFileName = DB_PATH + DB_NAME; 
     OutputStream mOutput = new FileOutputStream(outFileName); 
     byte[] mBuffer = new byte[1024]; 
     int mLength; 
     while ((mLength = mInput.read(mBuffer))>0) 
     { 
      mOutput.write(mBuffer, 0, mLength); 
     } 
     mOutput.flush(); 
     mOutput.close(); 
     mInput.close(); 
    } 

    //Open the database, so we can query it 
    public boolean openDataBase() throws SQLException 
    { 
     String mPath = DB_PATH + DB_NAME; 
     // Log.v("mPath", mPath); 
     mDataBase = SQLiteDatabase.openDatabase(mPath, null, SQLiteDatabase.CREATE_IF_NECESSARY); 

     return mDataBase != null; 
    } 

    @Override 
    public synchronized void close() 
    { 
     if(mDataBase != null) 
      mDataBase.close(); 
     super.close(); 
    } 


    @Override 
    public void onCreate(SQLiteDatabase db) { 

    } 

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

    } 
} 

應該在我的MainActivity.java上添加什麼？

public class MainActivity extends Activity { 

    private SQLiteDatabase database; 
    DataBaseHelper SBLdataCreate; 
    private static final String DB_NAME = "SBLdata.db"; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     DataBaseHelper dbOpenHelper = new DataBaseHelper(this, DB_NAME); 
     database = dbOpenHelper.openDataBase(); 
    } 

} 

Answer 1

您應該在試圖打開它並進行查詢之前創建數據庫。 在你的代碼中，我沒有看到你在創建數據庫之前打開它。

例如：

DataBaseHelper dbOpenHelper = new DataBaseHelper(this, DB_NAME); 
    dbOpenHelper.createDataBase() 
    database = dbOpenHelper.openDataBase(); 

Answer 2

這裏有一個更好的方式爲這你可能會工作:)

DataBaseHelper dbOpenHelper = new DataBaseHelper(this, DB_NAME); 

    try { 
    database = dbOpenHelper.createDataBase(); 
    } catch (IOException e) { 
    e.printStackTrace(); 
    } 
database = dbOpenHelper.openDataBase();