我有一个数据库，我把它放在我的资产文件夹中，我正在使用这个DataBaseHelper类。
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
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.onlywithalcohol/databases/";
private static String DB_NAME = "Alcohol_DB";
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) {
}
public boolean isOpen()
{
Log.v("test",myDataBase.getPath());
return myDataBase.isOpen();
}
public Cursor selectRecord(int id){
Cursor c =myDataBase.rawQuery("Select title from alcorecords where id="+id, null);
Log.v("test", c.toString());
return c;
}
// 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.
有人能告诉我如何做一个简单的选择函数吗？我做了这个功能
public Cursor selectRecord(int id){
Cursor c =myDataBase.rawQuery("Select title from alcorecords where id="+id, null);
Log.v("test", c.toString());
return c;
}
但如果告诉我数据库中没有这样的表，就会出错。我能做些什么来让这个孩子工作：）
最佳答案
上周我也遇到过类似的问题。我认为需要将文件扩展名附加到DB_NAME，这样它就变成"Alcohol_DB.sqlite"或".db"。之所以会得到消息“数据库中没有这样的表”，是因为即使创建空数据库也很困难—它不会从您的资源中复制您的数据库。
提示：
如果对数据库进行了任何更改，则应删除仿真器上的应用程序数据，以便它复制新数据库。为此，请转到Settings->Applications->Manage applications->YOUR_APP->Clear data。
如果使用eclipse，可以通过从模拟器下载数据库文件来检查文件是否已被复制。为此，您需要在eclipseWindow->Open perspective->Other...->DDMS中打开ddms透视图。选择左侧的模拟器并转到“文件资源管理器”选项卡。您可以在data/data/your.package.name/database/中找到您的数据库。选择文件并按选项卡右上角的“拉文件”按钮。现在可以使用首选的sqlite管理器检查该文件。
希望这有帮助！
编辑
我还将代码中的checkDataBase()更改为：
private boolean checkDataBase(){
String myPath = DB_PATH + DB_NAME;
File dbFile = new File(myPath);
return dbFile.exists();
}
关于java - 数据库Android从表中选择，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/14940054/