Android：錯誤聲明表在數據庫中不存在，但確實存在

Question

我在使用Android查詢SQLite數據庫時遇到問題。 我總是收到錯誤消息，說數據庫中不存在表“ users”，或者列名“ fname”不存在，但兩者都存在。

數據庫可識別的唯一表是android_metadata。 這是我的DataBaseHelper類的代碼：

public class DataBaseHelper extends SQLiteOpenHelper{

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

private static String DB_NAME = "CSLearnDB";

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;
}   


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 {

            this.close();
            copyDataBase();

        } catch (IOException e) {

            throw new Error("Error copying database");

        }
    }

    this.close();

}

/**
 * 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) {

}

public Cursor dbSelect(String table, String[] select){

    return myDataBase.query(table, select, null, null, null, null, null);

}

}

這是我的Main onCreate方法中的代碼：

public class Hello_AppActivity extends Activity {


String tag = "Events";

/** Called when the activity is first created. */

@Override
public void onCreate(Bundle savedInstanceState) {



    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    DataBaseHelper 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;

    }



    ArrayList<String> results = new ArrayList<String>();

    results.add("TEST");

    String[] x = {"sname"};

    Cursor c = myDbHelper.dbSelect("users", x);

    Spinner s1 = (Spinner) findViewById(R.id.spinner1);



    if (c != null ) {

        if  (c.moveToFirst()) {
            do {

                String firstName = c.getString(0);

                results.add(firstName);

                results.add("TEST 2");

            }while (c.moveToNext());
        } 
    }else{

    }

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, results);

    s1.setAdapter(adapter);

}

任何幫助將非常感激。 謝謝。

Answer 1

檢查並確保正確復制了數據庫。 如果該表實際上在其中，那么我敢打賭，空數據庫的創建早於您的想象，並且不會復制您想要的數據庫。

您應該能夠使用adb shell並在命令行上運行sqlite3來查詢數據庫。

Answer 2

是什么讓您確定它們的存在？ 您是否在SQLite瀏覽器中檢查了數據庫文件？

看起來您從未真正創建過表。 您將需要一條線

sqlDB.execSQL("create table users (_id integer primary key autoincrement, fname text);");

我將其放在助手的onCreate()方法中，但是您可以將其放置在其他位置。