如何将现有数据库与 Android 应用程序一起使用

How to use an existing database with an Android application(如何将现有数据库与 Android 应用程序一起使用)

问题描述

我已经创建了一个 SQLite 数据库.我想在我的 Android 项目中使用这个数据库文件.我想将此数据库与我的应用程序捆绑在一起.

I have already created an SQLite database. I want to use this database file with my Android project. I want to bundle this database with my application.

应用程序如何访问该数据库并将其用作其数据库，而不是创建一个新数据库?

Instead of creating a new database, how can the application gain access to this database and use it as its database?

推荐答案

注意:在尝试此代码之前，请在下面的代码中找到这一行:

NOTE: Before trying this code, please find this line in the below code:

private static String DB_NAME ="YourDbName"; // Database name

DB_NAME 这里是您的数据库的名称.假设您在assets文件夹中有数据库的副本，例如，如果您的数据库名称是ordersDB，那么DB_NAME的值将是ordersDB，

DB_NAME here is the name of your database. It is assumed that you have a copy of the database in the assets folder, so for example, if your database name is ordersDB, then the value of DB_NAME will be ordersDB,

private static String DB_NAME ="ordersDB";

<小时>

将数据库保存在 assets 文件夹中，然后按照以下步骤操作:

---

Keep the database in assets folder and then follow the below:

DataHelper 类:

DataHelper class:

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
    private static String DB_NAME ="YourDbName"; // Database name
    private static int DB_VERSION = 1; // Database version
    private final File DB_FILE;
    private SQLiteDatabase mDataBase;
    private final Context mContext;

    public DataBaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
        DB_FILE = context.getDatabasePath(DB_NAME);
        this.mContext = context;
    }

    public void createDataBase() throws IOException {
        // If the database does not exist, 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 file exists in databases folder
    private boolean checkDataBase() {
        return DB_FILE.exists();
    }

    // Copy the database from assets
    private void copyDataBase() throws IOException {
        InputStream mInput = mContext.getAssets().open(DB_NAME);
        OutputStream mOutput = new FileOutputStream(DB_FILE);
        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 {
        // Log.v("DB_PATH", DB_FILE.getAbsolutePath());
        mDataBase = SQLiteDatabase.openDatabase(DB_FILE, null, SQLiteDatabase.CREATE_IF_NECESSARY);
        // mDataBase = SQLiteDatabase.openDatabase(DB_FILE, null, SQLiteDatabase.NO_LOCALIZED_COLLATORS);
        return mDataBase != null;
    }

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

}

编写一个 DataAdapter 类，如:

import java.io.IOException;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

public class TestAdapter {

    protected static final String TAG = "DataAdapter";

    private final Context mContext;
    private SQLiteDatabase mDb;
    private DataBaseHelper mDbHelper;

    public TestAdapter(Context context) {
        this.mContext = context;
        mDbHelper = new DataBaseHelper(mContext);
    }

    public TestAdapter createDatabase() throws SQLException {
        try {
            mDbHelper.createDataBase();
        } catch (IOException mIOException) {
            Log.e(TAG, mIOException.toString() + "  UnableToCreateDatabase");
            throw new Error("UnableToCreateDatabase");
        }
        return this;
    }

    public TestAdapter open() throws SQLException {
        try {
            mDbHelper.openDataBase();
            mDbHelper.close();
            mDb = mDbHelper.getReadableDatabase();
        } catch (SQLException mSQLException) {
            Log.e(TAG, "open >>"+ mSQLException.toString());
            throw mSQLException;
        }
        return this;
    }

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

     public Cursor getTestData() {
         try {
             String sql ="SELECT * FROM myTable";
             Cursor mCur = mDb.rawQuery(sql, null);
             if (mCur != null) {
                mCur.moveToNext();
             }
             return mCur;
         } catch (SQLException mSQLException) {
             Log.e(TAG, "getTestData >>"+ mSQLException.toString());
             throw mSQLException;
         }
     }
}

现在你可以像这样使用它:

TestAdapter mDbHelper = new TestAdapter(urContext);
mDbHelper.createDatabase();
mDbHelper.open();

Cursor testdata = mDbHelper.getTestData();

mDbHelper.close();

感谢 JDx

对于 Android 4.1(果冻豆)，更改:

For Android 4.1 (Jelly Bean), change:

DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";

到:

DB_PATH = context.getApplicationInfo().dataDir + "/databases/";

在 DataHelper 类中，此代码适用于 Jelly Bean 4.2 多用户.

in the DataHelper class, this code will work on Jelly Bean 4.2 multi-users.

我们可以使用

DB_PATH = context.getDatabasePath(DB_NAME).getAbsolutePath();

这将为我们提供数据库文件的完整路径并适用于所有 Android 版本

which will give us the full path to the database file and works on all Android versions

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