如何将现有数据库与 Android 应用程序一起使用
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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