工作正常
这是从资源文件夹访问外部数据库的代码。在android中我们可以使用SQLite数据库浏览器创建sqlite数据库。现在的问题是如何在源代码中访问此数据库。答案很简单。将数据库存储在项目文件夹中的assets文件夹中。请在下面看到该答案。
请创建资产文件夹 - ＆gt; “您的”表示数据库名称
1）DatabaseHelper.class
public class DatabaseHelper extends SQLiteOpenHelper{
//The Android's default system path of your application database.
String DB_PATH =null;
private static String DB_NAME = "your";
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;
DB_PATH="/data/data/"+context.getPackageName()+"/"+"databases/";
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
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 {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* 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
try {
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY+SQLiteDatabase.NO_LOCALIZED_COLLATORS);
} catch (Exception e) {
// TODO: handle exception
}
}
@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) {
}
//return cursor
public Cursor query(String table,String[] columns, String selection,String[] selectionArgs,String groupBy,String having,String orderBy){
return myDataBase.query("cities", null, null, null, null, null, null);
}
}
2） CopyDbActivity.class
public class CopyDbActivity extends Activity {
/** Called when the activity is first created. */
Cursor c=null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
((Button)findViewById(R.id.button01)).setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
DatabaseHelper myDbHelper = new DatabaseHelper(CopyDbActivity.this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHelper.openDataBase();
}catch(SQLException sqle){
throw sqle;
}
Toast.makeText(CopyDbActivity.this, "Success", Toast.LENGTH_SHORT).show();
c=myDbHelper.query("cities", null, null, null, null,null, null);
if(c.moveToFirst())
{
do {
/*Toast.makeText(CopyDbActivity.this,
"_id: " + c.getString(0) + "\n" +
"E_NAME: " + c.getString(1) + "\n" +
"E_AGE: " + c.getString(2) + "\n" +
"E_DEPT: " + c.getString(3),
Toast.LENGTH_LONG).show();*/
} while (c.moveToNext());
}
}
});}
}
3） XML文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button android:id="@+id/button01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Copy Database">
</Button>
</LinearLayout>
答案 0 :(得分：0)
使用此
private static String DB_NAME = "your.db";
或
private static String DB_NAME = "your.sqlite";
而不是
private static String DB_NAME = "your";
答案 1 :(得分：0)
public class DatabaseOpenHelper extends OpenHelper {
private Context context;
private SQLiteDatabase sqliteDatabase;
private static String DB_PATH;
private static String DB_NAME;
public DatabaseOpenHelper(Context context, String name, CursorFactory factory) {
super(context, name, factory);
this.context = context;
this.DB_NAME = name;
this.DB_PATH = context.getString(R.string.DB_PATH);
try {
createDataBase();
} catch (Exception ioe) {
throw new Error("Unable to create database");
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
/** Open Database for Use */
public void openDatabase() {
String databasePath = DB_PATH + DB_NAME;
sqliteDatabase = SQLiteDatabase.openDatabase(databasePath, null,
(SQLiteDatabase.OPEN_READWRITE));
}
/** Close Database after use */
@Override
public synchronized void close() {
if ((sqliteDatabase != null) && sqliteDatabase.isOpen()) {
sqliteDatabase.close();
}
super.close();
}
/** Get database instance for use */
public SQLiteDatabase getSqliteDatabase() {
return sqliteDatabase;
}
/** Create new database if not present */
public void createDataBase() {
SQLiteDatabase sqliteDatabase = null;
if (databaseExists()) {
/* Check for Upgrade */
} else {
/* Database does not exists create blank database */
sqliteDatabase = this.getReadableDatabase();
sqliteDatabase.close();
copyDataBase();
}
}
/** Check Database if it exists */
private boolean databaseExists() {
SQLiteDatabase sqliteDatabase = null;
try {
String databasePath = DB_PATH + DB_NAME;
sqliteDatabase = SQLiteDatabase.openDatabase(databasePath, null,
SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
e.printStackTrace();
}
if (sqliteDatabase != null) {
sqliteDatabase.close();
}
return sqliteDatabase != null ? true : false;
}
/**
* Copy existing database file in system
*/
public void copyDataBase() {
int length;
byte[] buffer = new byte[1024];
String databasePath = DB_PATH + DB_NAME;
try {
InputStream databaseInputFile = this.context.getAssets().open(DB_NAME+".sqlite");
OutputStream databaseOutputFile = new FileOutputStream(databasePath);
while ((length = databaseInputFile.read(buffer)) > 0) {
databaseOutputFile.write(buffer, 0, length);
databaseOutputFile.flush();
}
databaseInputFile.close();
databaseOutputFile.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}