Android 数据库未打开我该怎么办？
当我执行cursor=execQuerySELECT+COL\u DISORDER\u NAME+FROM+TBL\u DISORDER list时；在日志cat上显示数据库未打开的语句。请帮帮我。如何从数据库中获取数据 多谢大家Android 数据库未打开我该怎么办？,android,Android,当我执行cursor=execQuerySELECT+COL\u DISORDER\u NAME+FROM+TBL\u DISORDER list时；在日志cat上显示数据库未打开的语句。请帮帮我。如何从数据库中获取数据 多谢大家 public class DBHelper extends SQLiteOpenHelper { public static String DB_PATH = ""; public static final String DB_NAME = "br
public class DBHelper extends SQLiteOpenHelper {
public static String DB_PATH = "";
public static final String DB_NAME = "braindatabse.db";
public static final int DB_VERSION = 1;
public static final String TBL_DISORDERLIST = "disorderlist";
public static final String COL_ROWID = "_id";
public static final String COL_DISORDER_NAME = "disordername";
public static final String COL_NICK_NAME = "nickname";
public static final String COL_DESCRIPTION = "description";
public static final String COL_TREATMENT = "treatment";
public static final String COL_PROGNOSIS = "prognosis";
public static SQLiteDatabase myDataBase;
public final Context myContext;
public static DBHelper mDBConnection;
/**
* Constructor Takes and keeps a reference of the passed context in order to
* access to the application assets and resources.
*
* @param context
*/
public DBHelper(Context context) {
super(context, DB_NAME, null, 1);
if(myDataBase != null && myDataBase.isOpen())
close();
this.myContext = context;
DB_PATH = "/data/data/"
+ context.getApplicationContext().getPackageName()
+ "/databases/";
// The Android's default system path of your application database is
// "/data/data/mypackagename/databases/"
try{
createDataBase();
openDataBase();
}catch(IOException e){
Log.i("db","Exception in creation of database : " + e.getMessage());
e.printStackTrace();
}
}
/**
* Creates an empty database on the system and rewrites it with your own database.
**/
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
Log.d("db", "creating db");
if(!dbExist)
{
this.getReadableDatabase();
try
{
//Copy the database from assests
copyDataBase();
Log.e("Err", "createDatabase database created");
}
catch (IOException mIOException)
{
throw new Error("ErrorCopyingDataBase");
}
}
}
/**
* 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 static boolean checkDataBase() {
/* File dbFile = new File(DB_PATH + DB_NAME);
Log.d("db", "dbFile exists");
return dbFile.exists();*/
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
Log.d("db", "db exists");
} catch (SQLiteException e) {
// database does't exist yet.
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* getting Instance
* @param context
* @return DBAdapter
*/
public static synchronized DBHelper getDBAdapterInstance(Context context) {
if (mDBConnection == null) {
mDBConnection = new DBHelper(context);
}
return mDBConnection;
}
/**
* 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();
Log.d("db", "database copied");
}
/**
* Open the database
* @throws SQLException
*/
public static void openDataBase() throws SQLException {
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
Log.d("db", "databse open");
}
public boolean isOpen()
{
if(myDataBase != null)
return myDataBase.isOpen();
return false;
}
public synchronized static void execNonQuery(String sql)
{
try
{
myDataBase.execSQL(sql);
//Log.d("SQL", sql);
}
catch ( Exception e )
{
Log.e("Err", e.getMessage());
}
finally
{
// closeDb();
}
}
public synchronized static Cursor execQuery(String sql)
{
Cursor cursor = null;
{
try
{
cursor = myDataBase.rawQuery(sql, null);
//Log.d("SQL", sql);
}
catch(Exception e)
{
Log.e("Err", "database not open");
}
}
return cursor;
}
/**
* Close the database if exist
*/
@Override
public synchronized void close() {
if (myDataBase != null)
myDataBase.close();
super.close();
}
/**
* Call on creating data base for example for creating tables at run time
*/
@Override
public void onCreate(SQLiteDatabase db) {
}
/**
* can used for drop tables then call onCreate(db) function to create tables
* again - upgrade
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
// ----------------------- CRUD Functions ------------------------------
/**
* This function used to select the records from DB.
* @param tableName
* @param tableColumns
* @param whereClase
* @param whereArgs
* @param groupBy
* @param having
* @param orderBy
* @return A Cursor object, which is positioned before the first entry.
*/
public Cursor selectRecordsFromDB(String tableName, String[] tableColumns,
String whereClase, String whereArgs[], String groupBy,
String having, String orderBy) {
return myDataBase.query(tableName, tableColumns, whereClase, whereArgs,
groupBy, having, orderBy);
}
public static List<Dboutput> readAll()
{
Cursor cursor =null;
try
{
List<Dboutput> all = new ArrayList<Dboutput>();
cursor = execQuery("SELECT " + COL_DISORDER_NAME + " FROM " + TBL_DISORDERLIST); // when this statement executes it shows error database not open
if(cursor.getCount() > 0)
{
int idIndex = cursor.getColumnIndex(COL_ROWID);
int nameIndex = cursor.getColumnIndex(COL_DISORDER_NAME);
int nicknameIndex = cursor.getColumnIndex(COL_NICK_NAME);
int descriptionIndex = cursor.getColumnIndex(COL_DESCRIPTION);
int treatmentIndex = cursor.getColumnIndex(COL_TREATMENT);
int prognosisIndex = cursor.getColumnIndex(COL_PROGNOSIS);
cursor.moveToFirst();
do
{
int id = cursor.getInt(idIndex);
String disorder_name = cursor.getString(nameIndex);
String nickname = cursor.getString(nicknameIndex);
String description = cursor.getString(descriptionIndex);
String treatment = cursor.getString(treatmentIndex);
String prognosis = cursor.getString(prognosisIndex);
Dboutput out = new Dboutput();
out.setId(id);
out.setdisorder_name(disorder_name);
out.setnick_name(nickname);
out.setdescription(description);
out.settreatment(treatment);
out.setprognosis(prognosis);
all.add(out);
cursor.moveToNext();
}while(!cursor.isAfterLast());
}
return (List<Dboutput>) all;
}
finally
{
if(cursor != null)
{
cursor.close();
}
}
}
若数据库不存在，为什么要在createDataBase中执行以下操作
boolean dbExist = checkDataBase();
if(!dbExist)
{
this.getReadableDatabase();
...
在查询数据库之前，您需要打开数据库
dataBaseHelper = new DataBaseHelper(context);
try {
dataBaseHelper.createDataBase();
dataBaseHelper.openDataBase();
} catch (Exception e) {
e.printStackTrace();
}
cursor.moveToFirst();
在on destroy中，您需要使用dataBaseHelper.close关闭数据库 要查找一个问题，有很多代码-您尝试过什么？你能提供一个关于这个问题的最简单的例子吗？我明白了，我在程序中犯了一个愚蠢的错误