如果您的应用程序需要一个数据库，并且它带有内置数据，那么交付该应用程序的最佳方式是什么?我应该:
预创建SQLite数据库，并将其包含在。apk? 在应用程序中包含SQL命令，并让它在第一次使用时创建数据库并插入数据?
我所看到的缺点是:
可能的SQLite版本不匹配可能会导致问题，我目前不知道数据库应该去哪里以及如何访问它。 在设备上创建和填充数据库可能需要很长时间。
有什么建议吗?关于任何问题的文档指针将非常感激。
当前回答
目前还没有办法预先创建一个SQLite数据库来与apk一起发布。最好的方法是将适当的SQL保存为资源，并从应用程序中运行它们。是的，这会导致数据的重复(同样的信息作为资源和数据库存在)，但目前没有其他方法。唯一的缓解因素是apk文件被压缩了。我的经验是908KB压缩到268KB以下。
下面的帖子有我找到的最好的讨论/解决方案，其中有很好的示例代码。
http://groups.google.com/group/android-developers/msg/9f455ae93a1cf152
我把我的CREATE语句存储为一个字符串资源，用Context.getString()读取，并用SQLiteDatabse.execSQL()运行。
我将插入的数据存储在res/raw/inserts中。sql(我创建了sql文件，7000+行)。使用上面链接的技术，我输入了一个循环，逐行读取文件，并将数据连接到“INSERT INTO tbl VALUE”，并执行另一个sqlitedatbase . execsql()。当它们可以连接时，保存7000个“INSERT INTO tbl VALUE”是没有意义的。
在模拟器上大约需要20秒，我不知道在真正的手机上需要多长时间，但它只发生一次，当用户第一次启动应用程序时。
其他回答
创建和更新数据库有两个选项。
One is to create a database externally, then place it in the assets folder of the project and then copy the entire database from there. This is much quicker if the database has a lot of tables and other components. Upgrades are triggered by changing the database version number in the res/values/strings.xml file. Upgrades would then be accomplished by creating a new database externally, replacing the old database in the assets folder with the new database, saving the old database in internal storage under another name, copying the new database from the assets folder into internal storage, transferring all of the data from the old database (that was renamed earlier) into the new database and finally deleting the old database. You can create a database originally by using the SQLite Manager FireFox plugin to execute your creation sql statements.
另一种选择是从sql文件内部创建数据库。这没有那么快，但是如果数据库只有几个表，用户可能不会注意到延迟。通过更改res/values/strings.xml文件中的数据库版本号来触发升级。然后通过处理一个升级sql文件来完成升级。数据库中的数据将保持不变，除非它的容器被删除，例如删除一个表。
下面的示例演示了如何使用这两种方法。
下面是一个create_database示例。sql文件。它将被放置在内部方法的项目资产文件夹中，或复制到SQLite管理器的“Execute SQL”中，以创建外部方法的数据库。(注意:注意关于Android需要的表的注释。)
--Android requires a table named 'android_metadata' with a 'locale' column
CREATE TABLE "android_metadata" ("locale" TEXT DEFAULT 'en_US');
INSERT INTO "android_metadata" VALUES ('en_US');
CREATE TABLE "kitchen_table";
CREATE TABLE "coffee_table";
CREATE TABLE "pool_table";
CREATE TABLE "dining_room_table";
CREATE TABLE "card_table";
下面是一个update_database示例。sql文件。它将被放置在内部方法的项目资产文件夹中，或复制到SQLite管理器的“Execute SQL”中，以创建外部方法的数据库。(注意:本例中包含的SQL解析器将忽略所有三种类型的SQL注释。)
--CREATE TABLE "kitchen_table"; This is one type of comment in sql. It is ignored by parseSql.
/*
* CREATE TABLE "coffee_table"; This is a second type of comment in sql. It is ignored by parseSql.
*/
{
CREATE TABLE "pool_table"; This is a third type of comment in sql. It is ignored by parseSql.
}
/* CREATE TABLE "dining_room_table"; This is a second type of comment in sql. It is ignored by parseSql. */
{ CREATE TABLE "card_table"; This is a third type of comment in sql. It is ignored by parseSql. }
--DROP TABLE "picnic_table"; Uncomment this if picnic table was previously created and now is being replaced.
CREATE TABLE "picnic_table" ("plates" TEXT);
INSERT INTO "picnic_table" VALUES ('paper');
下面是要添加到/res/values/strings.xml文件中的数据库版本号条目。
<item type="string" name="databaseVersion" format="integer">1</item>
下面是一个访问数据库并使用它的活动。(注意:如果数据库代码使用了大量资源，则可能需要在单独的线程中运行。)
package android.example;
import android.app.Activity;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
/**
* @author Danny Remington - MacroSolve
*
* Activity for demonstrating how to use a sqlite database.
*/
public class Database extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DatabaseHelper myDbHelper;
SQLiteDatabase myDb = null;
myDbHelper = new DatabaseHelper(this);
/*
* Database must be initialized before it can be used. This will ensure
* that the database exists and is the current version.
*/
myDbHelper.initializeDataBase();
try {
// A reference to the database can be obtained after initialization.
myDb = myDbHelper.getWritableDatabase();
/*
* Place code to use database here.
*/
} catch (Exception ex) {
ex.printStackTrace();
} finally {
try {
myDbHelper.close();
} catch (Exception ex) {
ex.printStackTrace();
} finally {
myDb.close();
}
}
}
}
这里是数据库助手类，如果需要，数据库将在其中创建或更新。(注意:Android要求你创建一个扩展SQLiteOpenHelper的类，以便使用Sqlite数据库。)
package android.example;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
/**
* @author Danny Remington - MacroSolve
*
* Helper class for sqlite database.
*/
public class DatabaseHelper extends SQLiteOpenHelper {
/*
* The Android's default system path of the application database in internal
* storage. The package of the application is part of the path of the
* directory.
*/
private static String DB_DIR = "/data/data/android.example/databases/";
private static String DB_NAME = "database.sqlite";
private static String DB_PATH = DB_DIR + DB_NAME;
private static String OLD_DB_PATH = DB_DIR + "old_" + DB_NAME;
private final Context myContext;
private boolean createDatabase = false;
private boolean upgradeDatabase = false;
/**
* 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, context.getResources().getInteger(
R.string.databaseVersion));
myContext = context;
// Get the path of the database that is based on the context.
DB_PATH = myContext.getDatabasePath(DB_NAME).getAbsolutePath();
}
/**
* Upgrade the database in internal storage if it exists but is not current.
* Create a new empty database in internal storage if it does not exist.
*/
public void initializeDataBase() {
/*
* Creates or updates the database in internal storage if it is needed
* before opening the database. In all cases opening the database copies
* the database in internal storage to the cache.
*/
getWritableDatabase();
if (createDatabase) {
/*
* If the database is created by the copy method, then the creation
* code needs to go here. This method consists of copying the new
* database from assets into internal storage and then caching it.
*/
try {
/*
* Write over the empty data that was created in internal
* storage with the one in assets and then cache it.
*/
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
} else if (upgradeDatabase) {
/*
* If the database is upgraded by the copy and reload method, then
* the upgrade code needs to go here. This method consists of
* renaming the old database in internal storage, create an empty
* new database in internal storage, copying the database from
* assets to the new database in internal storage, caching the new
* database from internal storage, loading the data from the old
* database into the new database in the cache and then deleting the
* old database from internal storage.
*/
try {
FileHelper.copyFile(DB_PATH, OLD_DB_PATH);
copyDataBase();
SQLiteDatabase old_db = SQLiteDatabase.openDatabase(OLD_DB_PATH, null, SQLiteDatabase.OPEN_READWRITE);
SQLiteDatabase new_db = SQLiteDatabase.openDatabase(DB_PATH,null, SQLiteDatabase.OPEN_READWRITE);
/*
* Add code to load data into the new database from the old
* database and then delete the old database from internal
* storage after all data has been transferred.
*/
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* 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 {
/*
* Close SQLiteOpenHelper so it will commit the created empty database
* to internal storage.
*/
close();
/*
* Open the database in the assets folder as the input stream.
*/
InputStream myInput = myContext.getAssets().open(DB_NAME);
/*
* Open the empty db in interal storage as the output stream.
*/
OutputStream myOutput = new FileOutputStream(DB_PATH);
/*
* Copy over the empty db in internal storage with the database in the
* assets folder.
*/
FileHelper.copyFile(myInput, myOutput);
/*
* Access the copied database so SQLiteHelper will cache it and mark it
* as created.
*/
getWritableDatabase().close();
}
/*
* This is where the creation of tables and the initial population of the
* tables should happen, if a database is being created from scratch instead
* of being copied from the application package assets. Copying a database
* from the application package assets to internal storage inside this
* method will result in a corrupted database.
* <P>
* NOTE: This method is normally only called when a database has not already
* been created. When the database has been copied, then this method is
* called the first time a reference to the database is retrieved after the
* database is copied since the database last cached by SQLiteOpenHelper is
* different than the database in internal storage.
*/
@Override
public void onCreate(SQLiteDatabase db) {
/*
* Signal that a new database needs to be copied. The copy process must
* be performed after the database in the cache has been closed causing
* it to be committed to internal storage. Otherwise the database in
* internal storage will not have the same creation timestamp as the one
* in the cache causing the database in internal storage to be marked as
* corrupted.
*/
createDatabase = true;
/*
* This will create by reading a sql file and executing the commands in
* it.
*/
// try {
// InputStream is = myContext.getResources().getAssets().open(
// "create_database.sql");
//
// String[] statements = FileHelper.parseSqlFile(is);
//
// for (String statement : statements) {
// db.execSQL(statement);
// }
// } catch (Exception ex) {
// ex.printStackTrace();
// }
}
/**
* Called only if version number was changed and the database has already
* been created. Copying a database from the application package assets to
* the internal data system inside this method will result in a corrupted
* database in the internal data system.
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
/*
* Signal that the database needs to be upgraded for the copy method of
* creation. The copy process must be performed after the database has
* been opened or the database will be corrupted.
*/
upgradeDatabase = true;
/*
* Code to update the database via execution of sql statements goes
* here.
*/
/*
* This will upgrade by reading a sql file and executing the commands in
* it.
*/
// try {
// InputStream is = myContext.getResources().getAssets().open(
// "upgrade_database.sql");
//
// String[] statements = FileHelper.parseSqlFile(is);
//
// for (String statement : statements) {
// db.execSQL(statement);
// }
// } catch (Exception ex) {
// ex.printStackTrace();
// }
}
/**
* Called everytime the database is opened by getReadableDatabase or
* getWritableDatabase. This is called after onCreate or onUpgrade is
* called.
*/
@Override
public void onOpen(SQLiteDatabase db) {
super.onOpen(db);
}
/*
* 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.
*/
}
下面是FileHelper类，它包含用于字节流复制文件和解析sql文件的方法。
package android.example;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.Reader;
import java.nio.channels.FileChannel;
/**
* @author Danny Remington - MacroSolve
*
* Helper class for common tasks using files.
*
*/
public class FileHelper {
/**
* Creates the specified <i><b>toFile</b></i> that is a byte for byte a copy
* of <i><b>fromFile</b></i>. If <i><b>toFile</b></i> already existed, then
* it will be replaced with a copy of <i><b>fromFile</b></i>. The name and
* path of <i><b>toFile</b></i> will be that of <i><b>toFile</b></i>. Both
* <i><b>fromFile</b></i> and <i><b>toFile</b></i> will be closed by this
* operation.
*
* @param fromFile
* - InputStream for the file to copy from.
* @param toFile
* - InputStream for the file to copy to.
*/
public static void copyFile(InputStream fromFile, OutputStream toFile) throws IOException {
// transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
try {
while ((length = fromFile.read(buffer)) > 0) {
toFile.write(buffer, 0, length);
}
}
// Close the streams
finally {
try {
if (toFile != null) {
try {
toFile.flush();
} finally {
toFile.close();
}
}
} finally {
if (fromFile != null) {
fromFile.close();
}
}
}
}
/**
* Creates the specified <i><b>toFile</b></i> that is a byte for byte a copy
* of <i><b>fromFile</b></i>. If <i><b>toFile</b></i> already existed, then
* it will be replaced with a copy of <i><b>fromFile</b></i>. The name and
* path of <i><b>toFile</b></i> will be that of <i><b>toFile</b></i>. Both
* <i><b>fromFile</b></i> and <i><b>toFile</b></i> will be closed by this
* operation.
*
* @param fromFile
* - String specifying the path of the file to copy from.
* @param toFile
* - String specifying the path of the file to copy to.
*/
public static void copyFile(String fromFile, String toFile) throws IOException {
copyFile(new FileInputStream(fromFile), new FileOutputStream(toFile));
}
/**
* Creates the specified <i><b>toFile</b></i> that is a byte for byte a copy
* of <i><b>fromFile</b></i>. If <i><b>toFile</b></i> already existed, then
* it will be replaced with a copy of <i><b>fromFile</b></i>. The name and
* path of <i><b>toFile</b></i> will be that of <i><b>toFile</b></i>. Both
* <i><b>fromFile</b></i> and <i><b>toFile</b></i> will be closed by this
* operation.
*
* @param fromFile
* - File for the file to copy from.
* @param toFile
* - File for the file to copy to.
*/
public static void copyFile(File fromFile, File toFile) throws IOException {
copyFile(new FileInputStream(fromFile), new FileOutputStream(toFile));
}
/**
* Creates the specified <i><b>toFile</b></i> that is a byte for byte a copy
* of <i><b>fromFile</b></i>. If <i><b>toFile</b></i> already existed, then
* it will be replaced with a copy of <i><b>fromFile</b></i>. The name and
* path of <i><b>toFile</b></i> will be that of <i><b>toFile</b></i>. Both
* <i><b>fromFile</b></i> and <i><b>toFile</b></i> will be closed by this
* operation.
*
* @param fromFile
* - FileInputStream for the file to copy from.
* @param toFile
* - FileInputStream for the file to copy to.
*/
public static void copyFile(FileInputStream fromFile, FileOutputStream toFile) throws IOException {
FileChannel fromChannel = fromFile.getChannel();
FileChannel toChannel = toFile.getChannel();
try {
fromChannel.transferTo(0, fromChannel.size(), toChannel);
} finally {
try {
if (fromChannel != null) {
fromChannel.close();
}
} finally {
if (toChannel != null) {
toChannel.close();
}
}
}
}
/**
* Parses a file containing sql statements into a String array that contains
* only the sql statements. Comments and white spaces in the file are not
* parsed into the String array. Note the file must not contained malformed
* comments and all sql statements must end with a semi-colon ";" in order
* for the file to be parsed correctly. The sql statements in the String
* array will not end with a semi-colon ";".
*
* @param sqlFile
* - String containing the path for the file that contains sql
* statements.
*
* @return String array containing the sql statements.
*/
public static String[] parseSqlFile(String sqlFile) throws IOException {
return parseSqlFile(new BufferedReader(new FileReader(sqlFile)));
}
/**
* Parses a file containing sql statements into a String array that contains
* only the sql statements. Comments and white spaces in the file are not
* parsed into the String array. Note the file must not contained malformed
* comments and all sql statements must end with a semi-colon ";" in order
* for the file to be parsed correctly. The sql statements in the String
* array will not end with a semi-colon ";".
*
* @param sqlFile
* - InputStream for the file that contains sql statements.
*
* @return String array containing the sql statements.
*/
public static String[] parseSqlFile(InputStream sqlFile) throws IOException {
return parseSqlFile(new BufferedReader(new InputStreamReader(sqlFile)));
}
/**
* Parses a file containing sql statements into a String array that contains
* only the sql statements. Comments and white spaces in the file are not
* parsed into the String array. Note the file must not contained malformed
* comments and all sql statements must end with a semi-colon ";" in order
* for the file to be parsed correctly. The sql statements in the String
* array will not end with a semi-colon ";".
*
* @param sqlFile
* - Reader for the file that contains sql statements.
*
* @return String array containing the sql statements.
*/
public static String[] parseSqlFile(Reader sqlFile) throws IOException {
return parseSqlFile(new BufferedReader(sqlFile));
}
/**
* Parses a file containing sql statements into a String array that contains
* only the sql statements. Comments and white spaces in the file are not
* parsed into the String array. Note the file must not contained malformed
* comments and all sql statements must end with a semi-colon ";" in order
* for the file to be parsed correctly. The sql statements in the String
* array will not end with a semi-colon ";".
*
* @param sqlFile
* - BufferedReader for the file that contains sql statements.
*
* @return String array containing the sql statements.
*/
public static String[] parseSqlFile(BufferedReader sqlFile) throws IOException {
String line;
StringBuilder sql = new StringBuilder();
String multiLineComment = null;
while ((line = sqlFile.readLine()) != null) {
line = line.trim();
// Check for start of multi-line comment
if (multiLineComment == null) {
// Check for first multi-line comment type
if (line.startsWith("/*")) {
if (!line.endsWith("}")) {
multiLineComment = "/*";
}
// Check for second multi-line comment type
} else if (line.startsWith("{")) {
if (!line.endsWith("}")) {
multiLineComment = "{";
}
// Append line if line is not empty or a single line comment
} else if (!line.startsWith("--") && !line.equals("")) {
sql.append(line);
} // Check for matching end comment
} else if (multiLineComment.equals("/*")) {
if (line.endsWith("*/")) {
multiLineComment = null;
}
// Check for matching end comment
} else if (multiLineComment.equals("{")) {
if (line.endsWith("}")) {
multiLineComment = null;
}
}
}
sqlFile.close();
return sql.toString().split(";");
}
}
目前还没有办法预先创建一个SQLite数据库来与apk一起发布。最好的方法是将适当的SQL保存为资源，并从应用程序中运行它们。是的，这会导致数据的重复(同样的信息作为资源和数据库存在)，但目前没有其他方法。唯一的缓解因素是apk文件被压缩了。我的经验是908KB压缩到268KB以下。
下面的帖子有我找到的最好的讨论/解决方案，其中有很好的示例代码。
http://groups.google.com/group/android-developers/msg/9f455ae93a1cf152
我把我的CREATE语句存储为一个字符串资源，用Context.getString()读取，并用SQLiteDatabse.execSQL()运行。
我将插入的数据存储在res/raw/inserts中。sql(我创建了sql文件，7000+行)。使用上面链接的技术，我输入了一个循环，逐行读取文件，并将数据连接到“INSERT INTO tbl VALUE”，并执行另一个sqlitedatbase . execsql()。当它们可以连接时，保存7000个“INSERT INTO tbl VALUE”是没有意义的。
在模拟器上大约需要20秒，我不知道在真正的手机上需要多长时间，但它只发生一次，当用户第一次启动应用程序时。
我修改了类和问题的答案，并编写了一个允许通过DB_VERSION更新数据库的类。
public class DatabaseHelper extends SQLiteOpenHelper {
private static String DB_NAME = "info.db";
private static String DB_PATH = "";
private static final int DB_VERSION = 1;
private SQLiteDatabase mDataBase;
private final Context mContext;
private boolean mNeedUpdate = false;
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
if (android.os.Build.VERSION.SDK_INT >= 17)
DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
else
DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
this.mContext = context;
copyDataBase();
this.getReadableDatabase();
}
public void updateDataBase() throws IOException {
if (mNeedUpdate) {
File dbFile = new File(DB_PATH + DB_NAME);
if (dbFile.exists())
dbFile.delete();
copyDataBase();
mNeedUpdate = false;
}
}
private boolean checkDataBase() {
File dbFile = new File(DB_PATH + DB_NAME);
return dbFile.exists();
}
private void copyDataBase() {
if (!checkDataBase()) {
this.getReadableDatabase();
this.close();
try {
copyDBFile();
} catch (IOException mIOException) {
throw new Error("ErrorCopyingDataBase");
}
}
}
private void copyDBFile() throws IOException {
InputStream mInput = mContext.getAssets().open(DB_NAME);
//InputStream mInput = mContext.getResources().openRawResource(R.raw.info);
OutputStream mOutput = new FileOutputStream(DB_PATH + DB_NAME);
byte[] mBuffer = new byte[1024];
int mLength;
while ((mLength = mInput.read(mBuffer)) > 0)
mOutput.write(mBuffer, 0, mLength);
mOutput.flush();
mOutput.close();
mInput.close();
}
public boolean openDataBase() throws SQLException {
mDataBase = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.CREATE_IF_NECESSARY);
return mDataBase != null;
}
@Override
public synchronized void close() {
if (mDataBase != null)
mDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (newVersion > oldVersion)
mNeedUpdate = true;
}
}
使用类。
在活动类中，声明变量。
private DatabaseHelper mDBHelper;
private SQLiteDatabase mDb;
在onCreate方法中，编写以下代码。
mDBHelper = new DatabaseHelper(this);
try {
mDBHelper.updateDataBase();
} catch (IOException mIOException) {
throw new Error("UnableToUpdateDatabase");
}
try {
mDb = mDBHelper.getWritableDatabase();
} catch (SQLException mSQLException) {
throw mSQLException;
}
如果将数据库文件添加到res/raw文件夹中，则使用类的以下修改。
public class DatabaseHelper extends SQLiteOpenHelper {
private static String DB_NAME = "info.db";
private static String DB_PATH = "";
private static final int DB_VERSION = 1;
private SQLiteDatabase mDataBase;
private final Context mContext;
private boolean mNeedUpdate = false;
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
if (android.os.Build.VERSION.SDK_INT >= 17)
DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
else
DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
this.mContext = context;
copyDataBase();
this.getReadableDatabase();
}
public void updateDataBase() throws IOException {
if (mNeedUpdate) {
File dbFile = new File(DB_PATH + DB_NAME);
if (dbFile.exists())
dbFile.delete();
copyDataBase();
mNeedUpdate = false;
}
}
private boolean checkDataBase() {
File dbFile = new File(DB_PATH + DB_NAME);
return dbFile.exists();
}
private void copyDataBase() {
if (!checkDataBase()) {
this.getReadableDatabase();
this.close();
try {
copyDBFile();
} catch (IOException mIOException) {
throw new Error("ErrorCopyingDataBase");
}
}
}
private void copyDBFile() throws IOException {
//InputStream mInput = mContext.getAssets().open(DB_NAME);
InputStream mInput = mContext.getResources().openRawResource(R.raw.info);
OutputStream mOutput = new FileOutputStream(DB_PATH + DB_NAME);
byte[] mBuffer = new byte[1024];
int mLength;
while ((mLength = mInput.read(mBuffer)) > 0)
mOutput.write(mBuffer, 0, mLength);
mOutput.flush();
mOutput.close();
mInput.close();
}
public boolean openDataBase() throws SQLException {
mDataBase = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.CREATE_IF_NECESSARY);
return mDataBase != null;
}
@Override
public synchronized void close() {
if (mDataBase != null)
mDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (newVersion > oldVersion)
mNeedUpdate = true;
}
}
http://blog.harrix.org/article/6784
我终于做到了!!我已经使用这个链接帮助在Android应用程序中使用自己的SQLite数据库，但必须稍微改变一下。
If you have many packages you should put the master package name here: private static String DB_PATH = "data/data/masterPakageName/databases"; I changed the method which copies the database from local folder to emulator folder! It had some problem when that folder didn't exist. So first of all, it should check the path and if it's not there, it should create the folder. In the previous code, the copyDatabase method was never called when the database didn't exist and the checkDataBase method caused exception. so I changed the code a little bit. If your database does not have a file extension, don't use the file name with one.
它对我很有用，我希望它对你也有用
package farhangsarasIntroduction;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.HashMap;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DataBaseHelper extends SQLiteOpenHelper{
//The Android's default system path of your application database.
private static String DB_PATH = "data/data/com.example.sample/databases";
private static String DB_NAME = "farhangsaraDb";
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() {
boolean dbExist;
try {
dbExist = checkDataBase();
} catch (SQLiteException e) {
e.printStackTrace();
throw new Error("database dose not exist");
}
if(dbExist){
//do nothing - database already exist
}else{
try {
copyDataBase();
} catch (IOException e) {
e.printStackTrace();
throw new Error("Error copying database");
}
//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();
}
}
/**
* 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.
throw new Error("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{
//copyDataBase();
//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;
File databaseFile = new File( DB_PATH);
// check if databases folder exists, if not create one and its subfolders
if (!databaseFile.exists()){
databaseFile.mkdir();
}
//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();
}
@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) {
}
you to create adapters for your views.
}
在Android Studio 3.0中附带数据库文件发布应用程序
对我来说，发布带有数据库文件的应用程序是个好主意。这样做的优点是不需要进行复杂的初始化，如果数据集很大，初始化有时会花费大量时间。
步骤1:准备数据库文件
准备好数据库文件。它可以是.db文件或.sqlite文件。如果您使用.sqlite文件，您所需要做的就是更改文件扩展名。步骤是一样的。
在本例中，我准备了一个名为testDB.db的文件。它有一个表和一些样本数据，像这样
步骤2:将文件导入到项目中
如果您还没有资产文件夹，请创建资产文件夹。然后将数据库文件复制并粘贴到此文件夹中
步骤3:复制文件到应用程序的数据文件夹
你需要将数据库文件复制到应用程序的数据文件夹中，以便与它进行进一步的交互。这是复制数据库文件的一次性操作(初始化)。如果多次调用此代码，data文件夹中的数据库文件将被assets文件夹中的数据库文件覆盖。当你想在未来的应用程序更新期间更新数据库时，这个覆盖过程是有用的。
注意，在应用程序更新期间，这个数据库文件不会在应用程序的数据文件夹中被更改。只有卸载才会删除它。
数据库文件需要复制到“/databases”文件夹下。打开设备文件资源管理器。输入data/data/<YourAppName>/ location。这是上面提到的应用程序的默认数据文件夹。默认情况下，数据库文件将放在该目录下的另一个名为databases的文件夹中
现在，复制文件的过程与Java所做的非常相似。使用下面的代码进行复制粘贴。这是起始代码。它还可以用于将来更新(通过覆盖)数据库文件。
//get context by calling "this" in activity or getActivity() in fragment
//call this if API level is lower than 17 String appDataPath = "/data/data/" + context.getPackageName() + "/databases/"
String appDataPath = context.getApplicationInfo().dataDir;
File dbFolder = new File(appDataPath + "/databases");//Make sure the /databases folder exists
dbFolder.mkdir();//This can be called multiple times.
File dbFilePath = new File(appDataPath + "/databases/testDB.db");
try {
InputStream inputStream = context.getAssets().open("testDB.db");
OutputStream outputStream = new FileOutputStream(dbFilePath);
byte[] buffer = new byte[1024];
int length;
while ((length = inputStream.read(buffer))>0)
{
outputStream.write(buffer, 0, length);
}
outputStream.flush();
outputStream.close();
inputStream.close();
} catch (IOException e){
//handle
}
然后刷新文件夹以验证复制过程
步骤4:创建数据库打开帮助程序
为SQLiteOpenHelper创建一个子类，包括连接、关闭、路径等。我把它命名为DatabaseOpenHelper
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseOpenHelper extends SQLiteOpenHelper {
public static final String DB_NAME = "testDB.db";
public static final String DB_SUB_PATH = "/databases/" + DB_NAME;
private static String APP_DATA_PATH = "";
private SQLiteDatabase dataBase;
private final Context context;
public DatabaseOpenHelper(Context context){
super(context, DB_NAME, null, 1);
APP_DATA_PATH = context.getApplicationInfo().dataDir;
this.context = context;
}
public boolean openDataBase() throws SQLException{
String mPath = APP_DATA_PATH + DB_SUB_PATH;
//Note that this method assumes that the db file is already copied in place
dataBase = SQLiteDatabase.openDatabase(mPath, null, SQLiteDatabase.OPEN_READWRITE);
return dataBase != null;
}
@Override
public synchronized void close(){
if(dataBase != null) {dataBase.close();}
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
步骤5:创建与数据库交互的顶级类
这将是读取和写入数据库文件的类。还有一个示例查询，用于打印数据库中的值。
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
public class Database {
private final Context context;
private SQLiteDatabase database;
private DatabaseOpenHelper dbHelper;
public Database(Context context){
this.context = context;
dbHelper = new DatabaseOpenHelper(context);
}
public Database open() throws SQLException
{
dbHelper.openDataBase();
dbHelper.close();
database = dbHelper.getReadableDatabase();
return this;
}
public void close()
{
dbHelper.close();
}
public void test(){
try{
String query ="SELECT value FROM test1";
Cursor cursor = database.rawQuery(query, null);
if (cursor.moveToFirst()){
do{
String value = cursor.getString(0);
Log.d("db", value);
}while (cursor.moveToNext());
}
cursor.close();
} catch (SQLException e) {
//handle
}
}
}
步骤6:测试运行
通过运行以下代码行来测试代码。
Database db = new Database(context);
db.open();
db.test();
db.close();
按下跑步键，欢呼吧!
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