Question

我在我的应用中预装了一张桌子。该表包含id，name和image，类型为blob。我按照this文章预加载数据库。数据库复制正常（根据日志）但我无法访问表名称。我试图打印名称，但表格是可访问的。这是我的代码：

MainActivity.java：

package com.arafatpiyada.preloadeddatabsedemo;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Repository repo = Repository.getInstance( this );

        repo.close();
        SQLiteDatabase db = repo.getWritableDatabase();

        if (db != null){

            Log.i("Database", db.getPath());
            Log.i("Database Details: ", Integer.toString(db.getVersion()));
        }


        Cursor c = db.rawQuery("SELECT name FROM sqlite_master WHERE type='table'", null);

        if (c.moveToFirst()) {
            while ( !c.isAfterLast() ) {

                Log.i("Table Content: ", c.getString(0));
                c.moveToNext();
            }
        }

    }


}

Repository.java

package com.arafatpiyada.preloadeddatabsedemo;
import android.content.Context;
import android.content.res.AssetManager;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class Repository extends SQLiteOpenHelper {

private static final int VERSION = 1;
    private static final String DATABASE_NAME = "fruits.db";
    private static File DATABASE_FILE;

    // This is an indicator if we need to copy the
    // database file.
    private boolean mInvalidDatabaseFile = false;
    private boolean mIsUpgraded = false;
    private Context mContext;

    /**
     * number of users of the database connection.
     * */
    private int mOpenConnections = 0;

    private static Repository mInstance;

    synchronized static public Repository getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new Repository(context.getApplicationContext());
        }
        return mInstance;
    }

    private Repository(Context context) {
        super(context, DATABASE_NAME, null, VERSION);
        this.mContext = context;

        SQLiteDatabase db = null;
        try {
            db = getReadableDatabase();
            if (db != null) {
                db.close();
            }

            DATABASE_FILE = context.getDatabasePath(DATABASE_NAME);

            if (mInvalidDatabaseFile) {
                copyDatabase();
            }
            if (mIsUpgraded) {
                doUpgrade();
            }
        } catch (SQLiteException e) {
        } finally {
            if (db != null && db.isOpen()) {
                db.close();
            }
        }
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        mInvalidDatabaseFile = true;
    }

    @Override
    public void onUpgrade(SQLiteDatabase database,
                          int old_version, int new_version) {
        mInvalidDatabaseFile = true;
        mIsUpgraded = true;
    }

    /**
     * called if a database upgrade is needed
     */
    private void doUpgrade() {
        // implement the database upgrade here.
    }

    @Override
    public synchronized void onOpen(SQLiteDatabase db) {
        super.onOpen(db);
        // increment the number of users of the database connection.
        mOpenConnections++;
        if (!db.isReadOnly()) {
            // Enable foreign key constraints
            db.execSQL("PRAGMA foreign_keys=ON;");
        }
    }

    /**
     * implementation to avoid closing the database connection while it is in
     * use by others.
     */
    @Override
    public synchronized void close() {
        mOpenConnections--;
        if (mOpenConnections == 0) {
            super.close();
        }
    }

    private void copyDatabase() {
        AssetManager assetManager = mContext.getResources().getAssets();
        InputStream in = null;
        OutputStream out = null;
        try {
            in = assetManager.open(DATABASE_NAME);
            out = new FileOutputStream(DATABASE_FILE);
            byte[] buffer = new byte[1024];
            int read = 0;
            while ((read = in.read(buffer)) != -1) {
                out.write(buffer, 0, read);
            }
        } catch (IOException e) {
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {}
            }
            if (out != null) {
                try {
                    out.close();
                } catch (IOException e) {}
            }
        }
        setDatabaseVersion();
        mInvalidDatabaseFile = false;
    }

    private void setDatabaseVersion() {
        SQLiteDatabase db = null;
        try {
            db = SQLiteDatabase.openDatabase(DATABASE_FILE.getAbsolutePath(), null,
                    SQLiteDatabase.OPEN_READWRITE);
            db.execSQL("PRAGMA user_version = " + VERSION);
        } catch (SQLiteException e ) {
        } finally {
            if (db != null && db.isOpen()) {
                db.close();
            }
        }
    }


}

Answer 1

我建议您使用Android SQLiteAssetHelper。它比您使用的代码更强大。

对于表名，改为使用您的查询：

SELECT name FROM sqlite_master WHERE type='table'

使用此查询：

SELECT name FROM sqlite_master WHERE type like 'table'

如果我没记错的话，我经常会发现使用＆＃39; = ＆＃39;选择不起作用，但始终使用喜欢。

数据库已复制但表空白

1 个答案: