我正在使用SQL开发一个简单的Android应用程序。我遵循了以下指南 - Using your own SQLite database in Android applications。
尝试对数据库进行查询时出错。
这是我的DataBaseHelp.Java类：
package namae.nombebe;
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.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class DataBaseHelper extends SQLiteOpenHelper{
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/namae.nombebe/databases/";
private static String DB_NAME = "myDBName";
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() 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
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@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) {
}
// 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.
}
我想做什么：
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DataBaseHelper myDbHelper = new DataBaseHelper(null);
myDbHelper = new DataBaseHelper(this);
try
{
myDbHelper.createDataBase();
}
catch (IOException ioe)
{
throw new Error("Unable to create database");
}
try
{
myDbHelper.openDataBase();
}
catch(SQLException sqle)
{
throw sqle;
}
myDataBase = myDbHelper.getWritableDatabase();
Cursor c = myDataBase.rawQuery("SELECT * FROM A", null);
//此查询的问题 }
所以我不知道出了什么问题。
我尝试使用简单的数据库名称“test.sqlite3”，有两个表“android_metadata”和“A”。
我做到了 INSERT INTO“android_metadata”VALUES（'en_US'）
在A中只有2列_id和TEXT，只有一个值“你好！”和“10”。
我遇到的错误是：
07-30 13：39：03.886：E / AndroidRuntime（307）：java.lang.RuntimeException：无法启动活动ComponentInfo {namae.nombebe / namae.nombebe.NomBebeActivity}：android.database.sqlite.SQLiteException：没有这样的表：A :,编译时：SELECT * FROM A
所以，如果有人有任何想法提前感谢。 我找了几个小时。
答案 0 :(得分：0)
您获得的错误未引用您的sqlite用法。您的活动存在一些问题
答案 1 :(得分：0)
当您实例化时，您的代码会创建一个空DB，然后您从您的活动中检查它并且它已经存在并且复制代码不会运行。因此，当您尝试查询时，表格不存在的消息。
示例DBAdapter类：
public class DBAdapter {
// tool groups table
public static final String TOOL_GROUP_TABLE = "ToolGroups";
public static final String TOOLGROUP_ROWID = "_id";
public static final String TOOLGROUP_DESCRIPTION = "GroupDescription";
// DB info
public static final String MAIN_DATABASE_NAME = "yourDB";
public static String MAIN_DB_PATH = "/data/data/your.package.name/databases/";
public static final int MAIN_DATABASE_VERSION = 1;
// database control
private DatabaseHelper mDbHelper;
private static SQLiteDatabase mDb;
private static Context mCtx;
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context, String dbname, int dbversion) {
super(context, dbname, null, dbversion);
if (checkDataBase(dbname)) {
openDataBase(dbname);
} else {
try {
this.getReadableDatabase();
copyDataBase(dbname);
this.close();
openDataBase(dbname);
} catch (IOException e) {
throw new Error("Error copying database");
}
Toast.makeText(context,
"Initial " + dbname + " database has been created",
Toast.LENGTH_LONG).show();
}
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
public DBAdapter(Context ctx) {
DBAdapter.mCtx = ctx;
}
public DBAdapter open(String dbname, int dbversion) throws SQLException {
mDbHelper = new DatabaseHelper(mCtx, dbname, dbversion);
mDb = mDbHelper.getWritableDatabase();
return this;
}
public void close() {
mDbHelper.close();
}
private static void copyDataBase(String dbname) throws IOException {
InputStream myInput = mCtx.getAssets().open(dbname);
String outFileName = MAIN_DB_PATH + dbname;
OutputStream myOutput = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
myOutput.flush();
myOutput.close();
myInput.close();
}
private static boolean checkDataBase(String dbname) {
SQLiteDatabase checkDB = null;
boolean exist = false;
try {
String db = MAIN_DB_PATH + dbname;
checkDB = SQLiteDatabase.openDatabase(db, null,
SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
Log.v("db log", "database does't exist");
}
if (checkDB != null) {
exist = true;
checkDB.close();
}
return exist;
}
private static void openDataBase(String dbname) throws SQLException {
String dbPath = MAIN_DB_PATH + dbname;
mDb = SQLiteDatabase.openDatabase(dbPath, null,
SQLiteDatabase.OPEN_READWRITE);
}
public Cursor fetchAllGroups() {
return mDb.query(TOOL_GROUP_TABLE, new String[] { TOOLGROUP_ROWID,
TOOLGROUP_DESCRIPTION }, null, null, null, null, null);
}
}
然后你可以从你的活动中调用它：
myDBHelper = new DBAdapter(this); // constructor copies database if it doesn't exist yet
myDBHelper.open(DBAdapter.MAIN_DATABASE_NAME, DBAdapter.MAIN_DATABASE_VERSION);
Cursor toolGroupCursor = mDBHelper.fetchAllGroups();