I am trying my hands on Windows phone 8 applications and I am stuck into a weird situation here. I am using sqlite in order to create sqlite db and add values into the database. I am able to create the database and add the values in the database successfully but I am having a weird situation here.
Everytime I close the emulator and start the project again the database gets created again which should not be happening because I created the db the very first time I run the application.
Does anybody know why, and how I can prevent it from recreating the database each time?
public string DB_PATH = Path.Combine(Path.Combine(ApplicationData.Current.LocalFolder.Path, "aa.sqlite"));
private SQLiteConnection dtCon;
public MainPage()
{
InitializeComponent();
CreateDatabase();
dtCon = new SQLiteConnection(DB_PATH);
var tp = dtCon.Query<Contacts>("select * from contacts").ToList();
}
private async void CreateDatabase()
{
bool isDatabaseExisting = false;
//Checking if database already exists
try
{
Windows.Storage.StorageFile storagefile = await Windows.Storage.ApplicationData.Current.LocalFolder.GetFileAsync("aa.sqlite");
isDatabaseExisting = true;
}
catch
{
isDatabaseExisting = false;
}
//if not exists then creating database
if (!isDatabaseExisting)
{
String str = System.IO.Path.Combine(Windows.Storage.ApplicationData.Current.LocalFolder.Path, "sqlite.db");
AddDataToDB(DB_PATH);
}
}
private void AddDataToDB(string str)
{
// Create the database connection.
dtCon = new SQLiteConnection(str);
// Create the table Task, if it doesn't exist.
dtCon.CreateTable<Contacts>();
Contacts oContacts = new Contacts();
oContacts.Name = "dfgdf";
oContacts.Detail = "asdfsf";
dtCon.Insert(oContacts);
}
I'm pretty sure when you close your emulator and restart, you're basically just uninstalling the application. Which is why your files or not there anymore -- as it looks like you're storing your data in isolated storage. I do not know if there is anyway around this.
You can buy a very cheap Windows 8/8.1 Phone and the files will persist until you manually uninstall the test application.
As #Chubosaurus says, closing and re-opening the emulator will remove all the apps. You can generally keep it running as long as you want and keep re-deploying your app to the emulator (although obviously rebooting the host PC will kill it).
You can save and restore the data from your emulator image via the ISETool command. See more here
Try adding Console.WriteLine("True"); and Console.WriteLine("False"); into the expected places after checking isDatabaseExisting to see/understand what the code path really is.
Related
I have started using the Xamarin plugin for Visual Studio to create an Android app.
I have a local SQL database, and I want to call it to display data. I don't see how I can do this. Is it possible?
After thinking this was a trivial thing to do, I was proven wrong when I tried setup a quick test project. This post will contain a full tutorial on setting up a DB for an Android App in Xamarin that will come in handy as a reference for future Xamarin users.
At a glance:
Add Sqlite.cs to your project.
Add your database file as an Asset.
Set your database file to build as an AndroidAsset.
Manually copy the database file out of your apk to another directory.
Open a database connetion using Sqlite.SqliteConnection.
Operate on the database using Sqlite.
Setting up a local database for a Xamarin Android project
1. Add Sqlite.cs to your project.
Start by going to this repository and downloading Sqlite.cs; this provides the Sqlite API that you can use to run queries against your db. Add the file to your project as a source file.
2. Add DB as asset.
Next, get your DB and copy it into the Assets directory of your Android project and then import it into your project so that it appears beneath the Assets folder within your solution:
I'm using the Chinook_Sqlite.sqlite database sample renamed to db.sqlite from this site throughout this example.
3. Set DB to build as AndroidAsset.
Right click on the DB file and set it to build action AndroidAsset. This will ensure that it is included into the assets directory of the APK.
4. Manually copy DB out of your APK.
As the DB is included as an Asset (packaged within the APK) you will need to extract it out.
You can do this with the following code:
string dbName = "db.sqlite";
string dbPath = Path.Combine (Android.OS.Environment.ExternalStorageDirectory.ToString (), dbName);
// Check if your DB has already been extracted.
if (!File.Exists(dbPath))
{
using (BinaryReader br = new BinaryReader(Android.App.Application.Context.Assets.Open(dbName)))
{
using (BinaryWriter bw = new BinaryWriter(new FileStream(dbPath, FileMode.Create)))
{
byte[] buffer = new byte[2048];
int len = 0;
while ((len = br.Read(buffer, 0, buffer.Length)) > 0)
{
bw.Write (buffer, 0, len);
}
}
}
}
This extracts the DB as a binary file from the APK and places it into the system external storage path. Realistically the DB can go wherever you want, I've just chosen to stick it here.
I also read that Android has a databases folder that will store databases directly; I couldn't get it to work so I've just ran with this method of using an existing DB.
5. Open DB Connection.
Now open a connection to the DB through the Sqlite.SqliteConnection class:
using (var conn = new SQLite.SQLiteConnection(dbPath))
{
// Do stuff here...
}
6. Operate on DB.
Lastly, as Sqlite.net is an ORM, you can operate on the database using your own data types:
public class Album
{
[PrimaryKey, AutoIncrement]
public int AlbumId { get; set; }
public string Title { get; set; }
public int ArtistId { get; set; }
}
// Other code...
using (var conn = new SQLite.SQLiteConnection(dbPath))
{
var cmd = new SQLite.SQLiteCommand (conn);
cmd.CommandText = "select * from Album";
var r = cmd.ExecuteQuery<Album> ();
Console.Write (r);
}
Summary
And that's how to add an existing Sqlite database to your Xamarin solution for Android! For more information check out the examples included with the Sqlite.net library, its unit tests and the examples in the Xamarin documentation.
Here is the one that I'm using and it's working
install the Sqlite plugin
create interface to access different platforms services
create a model for the table
implement the interface that you created earlier on all of the
platform you want to use
use the plugin to create, get, insert, etc on your table
for more detailed information check this
i have created the data base in windows phone 7 and it works me fine
after rebuild the application it says that
The database file cannot be found. Check the path to the database. [ Data Source = \Applications\Data\6157CB94-31D3-4E6F-BFC3-78BE1549C10A\Data\IsolatedStore\amit.sdf ]
my code for db string is
` private const string Con_String = #"isostore:/amit.sdf";`
how to solve this pls give me any suggestion to solve this problem
Have you checked this sample How to create a basic local database app for Windows Phone?
they use this path for create the db
//Specify the connection string as a static, used in main page and app.xaml.
public static string DBConnectionString = "Data Source=isostore:/ToDo.sdf";
and also don't forget to check if the db exists
//Create the database if it does not exist.
using (ToDoDataContext db = new ToDoDataContext(ToDoDataContext.DBConnectionString))
{
if (db.DatabaseExists() == false)
{
//Create the database
db.CreateDatabase();
}
}
I dont know what's happenning.
This is my code:
public class MyApp extends MainScreen {
Database sqliteDB;
URI uri;
String name;
public MyApp()
{
try{
uri = URI.create("file:///SDCard/Databases/sample/" +"prueba.db");
sqliteDB = DatabaseFactory.create(uri);
sqliteDB = DatabaseFactory.open(uri);
Statement st = sqliteDB.createStatement("CREATE TABLE joke(name)");
st.prepare();
st.execute();
st.close();
Statement st1 = sqliteDB.createStatement("INSERT INTO joke VALUES ('Maxo')");
st1.prepare();
st1.execute();
st1.close();
Statement st2 = sqliteDB.createStatement("INSERT INTO joke VALUES ('Lala')");
st2.prepare();
st2.execute();
st2.close();
/*
Statement st1 = sqliteDB.createStatement("SELECT * from joke");
st1.prepare();
Cursor c = st1.getCursor();
Row r;
while(c.next()) {
r = c.getRow();
name = r.getString(0);
}
st1.execute();
st1.close();*/
sqliteDB.close();
add(new RichTextField("Status: Database was created and inserted the values successfully"));
//add(new RichTextField(""+name));
}
catch (Exception e){
System.out.println(e.getMessage());
e.printStackTrace();
}
}
}
Im just creating a database, a table and inserting two fields. So what i do is first execute emulator, set a directory to my sdcard. Well after that i execute my program, and sometimes it creates the database in that directoy, sometimes not, sometimes it creates database without table or data.. i dont know why, i tried 8520 9550 emulator, but its rare whats happenning with database and sdcard. Anyone has an idea of what could be happenning? Its annoying to be coding and sometimes it works sometimes not and you dont know why.. And its not coding problem i think, because sometimes it works :S
Make sure u have mounted your SD card.Double click on the folder where you want to save your database and then tick the checkbox for remounting it on next emulator run.
Hope it helps.
I put my database field in "assets" folder. And use the code from this blog to copy the database to "/data/data/my_packname/databases/", (This copy code i run it in the onCreate() method when i run this app) then use select * from ... to get data. But it gives me the exception: no such table.
Someone told me that if i am attempting to copy the file in SQLiteOpenHelper's onCreate(), it's too late. So the copy file code can not copy the complete file.
So i need to use adb or ddms to pull the database first?
So, Anyone can teach me how to use my own databse?
Can you tell me the setup?
I've used the instructions in that blog post and found them, while on the right track, to severely complicate the issue by unnecessarily extending SQLiteOpenHelper. I've had much better luck doing the following:
Create a utility class that creates the static db by copying it into the correct directory from assets, but doesn't get itself so hung up on following the SQLiteOpenHelper format.
Using the same utility class to open the db by using SQLiteDatabase.openDatabase()
Edit: Here is a version of this utility class I've created; it's not quite complete, but you'll get the drift.
public class DbUtils {
private static final String DB_PATH = "/data/data/com.mypackage.myapp/databases/";
private static final String DB_NAME = "my.db";
public static void createDatabaseIfNotExists(Context context) throws IOException {
boolean createDb = false;
File dbDir = new File(DB_PATH);
File dbFile = new File(DB_PATH + DB_NAME);
if (!dbDir.exists()) {
dbDir.mkdir();
createDb = true;
}
else if (!dbFile.exists()) {
createDb = true;
}
else {
// Check that we have the latest version of the db
boolean doUpgrade = false;
// Insert your own logic here on whether to upgrade the db; I personally
// just store the db version # in a text file, but you can do whatever
// you want. I've tried MD5 hashing the db before, but that takes a while.
// If we are doing an upgrade, basically we just delete the db then
// flip the switch to create a new one
if (doUpgrade) {
dbFile.delete();
createDb = true;
}
}
if (createDb) {
// Open your local db as the input stream
InputStream myInput = context.getAssets().open(DB_NAME);
// Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(dbFile);
// 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 static SQLiteDatabase getStaticDb() {
return SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READONLY);
}
}
After you've copied the database, you should try closing and reopening the SQLiteDatabase object before executing any query on it. I had a similar problem with copying a db from an input stream and that's what solved it for me.
here is my Version from "Silvio Donnini" Code :),
now you can update the Database easily.
private static final String DB_PATH = "/data/data/pakagename/databases/";
private static final String DB_NAME = "databaseName";
private static SQLiteDatabase db;
public static void createDatabaseIfNotExists(Context context,int version) throws IOException {
boolean createDb = false;
File dbDir = new File(DB_PATH);
File dbFile = new File(DB_PATH + DB_NAME);
if (!dbDir.exists()) {
dbDir.mkdir();
createDb = true;
}
else if (!dbFile.exists()) {
createDb = true;
}
else {
// Check that we have the latest version of the db
db = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READONLY);
if (db.getVersion() != version) {
dbFile.delete();
createDb = true;
}
}
if (createDb) {
// Open your local db as the input stream
InputStream myInput = context.getResources().openRawResource(R.raw.database);
// Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(dbFile);
// 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();
SQLiteDatabase dbwrite = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READWRITE);
dbwrite.setVersion(version);
dbwrite.close();
if (db != null)
db = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READONLY);
}
}
public static SQLiteDatabase getStaticDb() {
if (db != null)
return db;
return SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READONLY);
}
I know this is an old question, but I lost a lot of time figuring it out, with the help of all the replies.
The issue is that a device stores a database in his data/data/.../databases folder. So, when you change sth about the database (name, add android metadata table, size..) it wont make any difference because of the stored database and the method that checked for existing database.
To get the newest database, after changing it, you must run the program without checking for existing databses (e.g. instead of dbExist = checkDataBase(); make it just false).
dbExist = checkDataBase();
Change to:
dbExists = false;
After you picked up the "new" databse you can return to checking the existing ones.
Hope it helps someone,
dina
I know this is an old post, but for those who still get here after a Google or a Bing search, this is the solution to the stated problem:
in createDataBase() there is the following check;
this.getReadableDatabase();
This checks if there is already a database with the provided name and if not creates an empty database such that it can be overwritten with the one in the assets folder. On newer devices this works flawlessly but there are some devices on which this doesn't work. Mainly older devices. I do not know exactly why, but it seems like the getReadableDatabase() function not only gets the database but also opens it. If you then copy the database from the assets folder over it, it still has the pointer to an empty database and you will get table does not exist errors.
So in order to make it work on all devices you should modify it to the following lines:
SQLiteDatabase db = this.getReadableDatabase();
if (db.isOpen()){
db.close();
}
Even if the database is opened in the check, it is closed thereafter and it will not give you any more trouble.
Calm down guys,After long research finally found silly mistake for "no such table" error
Check name of database in Assets folder if it's like "DATABASE_NAME.EXTENSION" then put full name in Helper class with extension its solved my problem.
like say in Assets name of database is login.sqlite or login.db anything. put DB_NAME=login.sqlite fully with extention.
this tutorial now works perfectly.
The way of creating database from article you've posted is slightly diffrent from that how it's done in android examples (I don't want to say if it's good or bad).
I've learned how to use databases from SDKs NotePad sample
It's good example to start from, becouse it covers both database creation topic and database access through ContentProvider (it's really the only good way to get data from db, otherwise you will have problems when trying to get data simultaneusly from many places of your code).
You should note that SQLiteOpenHelper is really powerful and "it will help you" if you will use it properly. For example it stores current database version (not sqlite version but number you assingn with database schema version) and when you create new application version with new database structure you can update current schema to the new version in onUpdate.
Here is some background about my app:
I am developing an Android app that will display a random quote or verse to the user. For this I am using an SQLite database. The size of the DB would be approximately 5K to 10K records, possibly increasing to upto 1M in later versions as new quotes and verses are added. Thus the user would need to update the DB as and when newer versions are of the app or DB are released.
After reading through some forums online, there seem to be two feasible ways I could provide the DB:
1. Bundle it along with the .APK file of the app, or
2. Upload it to my app's website from where users will have to download it
I want to know which method would be better (if there is yet another approach other than these, please do let me know).
After pondering this problem for some time, I have these thoughts regarding the above approaches:
Approach 1:
Users will obtain the DB along with the app, and won't have to download it separately. Installation would thereby be easier. But, users will have to reinstall the app every time there is a new version of the DB. Also, if the DB is large, it will make the installable too cumbersome.
Approach 2:
Users will have to download the full DB from the website (although I can provide a small, sample version of the DB via Approach 1). But, the installer will be simpler and smaller in size. Also, I would be able to provide future versions of the DB easily for those who might not want newer versions of the app.
Could you please tell me from a technical and an administrative standpoint which approach would be the better one and why?
If there is a third or fourth approach better than either of these, please let me know.
Thank you!
Andruid
I built a similar app for Android which gets periodic updates with data from a government agency. It's fairly easy to build an Android compatible db off the device using perl or similar and download it to the phone from a website; and this works rather well, plus the user gets current data whenever they download the app. It's also supposed to be possible to throw the data onto the sdcard if you want to avoid using primary data storage space, which is a bigger concern for my app which has a ~6Mb database.
In order to make Android happy with the DB, I believe you have to do the following (I build my DB using perl).
$st = $db->prepare( "CREATE TABLE \"android_metadata\" (\"locale\" TEXT DEFAULT 'en_US')");
$st->execute();
$st = $db->prepare( "INSERT INTO \"android_metadata\" VALUES ('en_US')");
$st->execute();
I have an update activity which checks weather updates are available and if so presents an "update now" screen. The download process looks like this and lives in a DatabaseHelperClass.
public void downloadUpdate(final Handler handler, final UpdateActivity updateActivity) {
URL url;
try {
close();
File f = new File(getDatabasePath());
if (f.exists()) {
f.delete();
}
getReadableDatabase();
close();
url = new URL("http://yourserver.com/" + currentDbVersion + ".sqlite");
URLConnection urlconn = url.openConnection();
final int contentLength = urlconn.getContentLength();
Log.i(TAG, String.format("Download size %d", contentLength));
handler.post(new Runnable() {
public void run() {
updateActivity.setProgressMax(contentLength);
}
});
InputStream is = urlconn.getInputStream();
// Open the empty db as the output stream
OutputStream os = new FileOutputStream(f);
// transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024 * 1000];
int written = 0;
int length = 0;
while (written < contentLength) {
length = is.read(buffer);
os.write(buffer, 0, length);
written += length;
final int currentprogress = written;
handler.post(new Runnable() {
public void run() {
Log.i(TAG, String.format("progress %d", currentprogress));
updateActivity.setCurrentProgress(currentprogress);
}
});
}
// Close the streams
os.flush();
os.close();
is.close();
Log.i(TAG, "Download complete");
openDatabase();
} catch (Exception e) {
Log.e(TAG, "bad things", e);
}
handler.post(new Runnable() {
public void run() {
updateActivity.refreshState(true);
}
});
}
Also note that I keep a version number in the filename of the db files, and a pointer to the current one in a text file on the server.
It sounds like your app and your db are tightly bound -- that is, the db is useless without the database and the database is useless without the app, so I'd say go ahead and put them both in the same .apk.
That being said, if you expect the db to change very slowly over time, but the app to change quicker, and you don't want your users to have to download the db with each new app revision, then you might want to unbundle them. To make this work, you can do one of two things:
Install them as separate applications, but make sure they share the same userID using the sharedUserId tag in the AndroidManifest.xml file.
Install them as separate applications, and create a ContentProvider for the database. This way other apps could make use of your database as well (if that is useful).
If you are going to store the db on your website then I would recommend that you just make rpc calls to your webserver and get data that way, so the device will never have to deal with a local database. Using a cache manager to avoid multiple lookups will help as well so pages will not have to lookup data each time a page reloads. Also if you need to update the data you do not have to send out a new app every time. Using HttpClient is pretty straight forward, if you need any examples please let me know