查询不起作用android sqlite

Question

我正在用SQL开发一个简单的Android应用程序。我遵循以下指南 - Using your own SQLite database in Android applications。

试图执行查询数据库时出现错误。

这里是我的DataBaseHelp.Java类：

package namae.nombebe; 

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.SQLiteException; 
import android.database.sqlite.SQLiteOpenHelper; 

public class DataBaseHelper extends SQLiteOpenHelper{ 

    //The Android's default system path of your application database. 
    private static String DB_PATH = "/data/data/namae.nombebe/databases/"; 

    private static String DB_NAME = "myDBName"; 

    private SQLiteDatabase myDataBase; 

    private final Context myContext; 

    /** 
    * Constructor 
    * Takes and keeps a reference of the passed context in order to access to the application assets and resources. 
    * @param context 
    */ 
    public DataBaseHelper(Context context) { 

     super(context, DB_NAME, null, 1); 
     this.myContext = context; 
    } 

    /** 
    * Creates a empty database on the system and rewrites it with your own database. 
    * */ 
    public void createDataBase() throws IOException{ 

     boolean dbExist = checkDataBase(); 

     if(dbExist){ 
      //do nothing - database already exist 
     }else{ 

      //By calling this method and empty database will be created into the default system path 
       //of your application so we are gonna be able to overwrite that database with our database. 
      this.getReadableDatabase(); 

      try { 

       copyDataBase(); 

      } catch (IOException e) { 

       throw new Error("Error copying database"); 

      } 
     } 

    } 

    /** 
    * Check if the database already exist to avoid re-copying the file each time you open the application. 
    * @return true if it exists, false if it doesn't 
    */ 
    private boolean checkDataBase(){ 

     SQLiteDatabase checkDB = null; 

     try{ 
      String myPath = DB_PATH + DB_NAME; 
      checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY); 

     }catch(SQLiteException e){ 

      //database does't exist yet. 

     } 

     if(checkDB != null){ 

      checkDB.close(); 

     } 

     return checkDB != null ? true : false; 
    } 

    /** 
    * Copies your database from your local assets-folder to the just created empty database in the 
    * system folder, from where it can be accessed and handled. 
    * This is done by transfering bytestream. 
    * */ 
    private void copyDataBase() throws IOException{ 

     //Open your local db as the input stream 
     InputStream myInput = myContext.getAssets().open(DB_NAME); 

     // Path to the just created empty db 
     String outFileName = DB_PATH + DB_NAME; 

     //Open the empty db as the output stream 
     OutputStream myOutput = new FileOutputStream(outFileName); 

     //transfer bytes from the inputfile to the outputfile 
     byte[] buffer = new byte[1024]; 
     int length; 
      while ((length = myInput.read(buffer))>0){ 
      myOutput.write(buffer, 0, length); 
     } 

     //Close the streams 
     myOutput.flush(); 
     myOutput.close(); 
     myInput.close(); 

    } 

    public void openDataBase() throws SQLException{ 

     //Open the database 
     String myPath = DB_PATH + DB_NAME; 
     myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY); 

    } 

    @Override 
    public synchronized void close() { 

      if(myDataBase != null) 
       myDataBase.close(); 

      super.close(); 

    } 

    @Override 
    public void onCreate(SQLiteDatabase db) { 

    } 

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

    } 

     // Add your public helper methods to access and get content from the database. 
     // You could return cursors by doing "return myDataBase.query(....)" so it'd be easy 
     // to you to create adapters for your views. 
} 

什么，我试图做的：

public void onCreate(Bundle savedInstanceState) 
{ 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 

    DataBaseHelper myDbHelper = new DataBaseHelper(null); 
    myDbHelper = new DataBaseHelper(this); 

    try 
    { 
      myDbHelper.createDataBase(); 
    } 
    catch (IOException ioe) 
    { 
     throw new Error("Unable to create database"); 
    } 

    try 
    { 
     myDbHelper.openDataBase(); 
    } 
    catch(SQLException sqle) 
    { 
     throw sqle; 
    } 

    myDataBase = myDbHelper.getWritableDatabase(); 

    Cursor c = myDataBase.rawQuery("SELECT * FROM A", null); 

//问题在此查询 }

所以我没有任何想法出了什么问题。

我试着简单的数据库名称“test.sqlite3”，有两个表“android_metadata”和“A”。

我已经做了 INSERT INTO “android_metadata” VALUES（ 'EN_US'）

，并在那里只有2列_id和文字，只有一个值 “你好！”和“10”。

我有错误是：

07-30 13：39：03.886：E/AndroidRuntime（307）：了java.lang.RuntimeException：无法启动活动ComponentInfo {namae.nombebe/namae。 nombebe.NomBebeActivity}：android.database.sqlite.SQLiteException：没有这样的表：A：，编译时：SELECT * FROM A

所以，如果任何人有任何想法，在此先感谢。 我要找几个小时。

Answer 1

当您实例化时，您的代码将创建一个空的数据库，然后从您的活动中检查该数据库，并且该数据库已存在，并且复制代码不会运行。因此，当您尝试查询时，您的表不存在的消息。

一个例子将对DBAdapter类：

public class DBAdapter { 

    // tool groups table 
    public static final String TOOL_GROUP_TABLE = "ToolGroups"; 
    public static final String TOOLGROUP_ROWID = "_id"; 
    public static final String TOOLGROUP_DESCRIPTION = "GroupDescription"; 

    // DB info 
    public static final String MAIN_DATABASE_NAME = "yourDB"; 
    public static String MAIN_DB_PATH = "/data/data/your.package.name/databases/"; 
    public static final int MAIN_DATABASE_VERSION = 1; 

    // database control 
    private DatabaseHelper mDbHelper; 
    private static SQLiteDatabase mDb; 
    private static Context mCtx; 

    private static class DatabaseHelper extends SQLiteOpenHelper { 
     DatabaseHelper(Context context, String dbname, int dbversion) { 
      super(context, dbname, null, dbversion); 
      if (checkDataBase(dbname)) { 
       openDataBase(dbname); 
      } else { 
       try { 
        this.getReadableDatabase(); 
        copyDataBase(dbname); 
        this.close(); 
        openDataBase(dbname); 
       } catch (IOException e) { 
        throw new Error("Error copying database"); 
       } 
       Toast.makeText(context, 
         "Initial " + dbname + " database has been created", 
         Toast.LENGTH_LONG).show(); 
      } 
     } 

     @Override 
     public void onCreate(SQLiteDatabase db) { 
     } 

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

    public DBAdapter(Context ctx) { 
     DBAdapter.mCtx = ctx; 
    } 

    public DBAdapter open(String dbname, int dbversion) throws SQLException { 
     mDbHelper = new DatabaseHelper(mCtx, dbname, dbversion); 
     mDb = mDbHelper.getWritableDatabase(); 
     return this; 
    } 

    public void close() { 
     mDbHelper.close(); 
    } 

    private static void copyDataBase(String dbname) throws IOException { 
     InputStream myInput = mCtx.getAssets().open(dbname); 
     String outFileName = MAIN_DB_PATH + dbname; 
     OutputStream myOutput = new FileOutputStream(outFileName); 
     byte[] buffer = new byte[1024]; 
     int length; 
     while ((length = myInput.read(buffer)) > 0) { 
      myOutput.write(buffer, 0, length); 
     } 
     myOutput.flush(); 
     myOutput.close(); 
     myInput.close(); 
    } 

    private static boolean checkDataBase(String dbname) { 
     SQLiteDatabase checkDB = null; 
     boolean exist = false; 
     try { 
      String db = MAIN_DB_PATH + dbname; 
      checkDB = SQLiteDatabase.openDatabase(db, null, 
        SQLiteDatabase.OPEN_READONLY); 
     } catch (SQLiteException e) { 
      Log.v("db log", "database does't exist"); 
     } 
     if (checkDB != null) { 
      exist = true; 
      checkDB.close(); 
     } 
     return exist; 
    } 

    private static void openDataBase(String dbname) throws SQLException { 
     String dbPath = MAIN_DB_PATH + dbname; 
     mDb = SQLiteDatabase.openDatabase(dbPath, null, 
       SQLiteDatabase.OPEN_READWRITE); 
    } 

    public Cursor fetchAllGroups() { 
     return mDb.query(TOOL_GROUP_TABLE, new String[] { TOOLGROUP_ROWID, 
      TOOLGROUP_DESCRIPTION }, null, null, null, null, null); 
    } 
} 

然后你从你的活动这样称呼它：

myDBHelper = new DBAdapter(this); // constructor copies database if it doesn't exist yet 
myDBHelper.open(DBAdapter.MAIN_DATABASE_NAME, DBAdapter.MAIN_DATABASE_VERSION); 
Cursor toolGroupCursor = mDBHelper.fetchAllGroups(); 

Answer 2

你得到的错误没有引用到你的sqlite的用法。您的活动存在一些问题