Xamarin.Forms: Cannot connect to database - sql

Question

I have this database structure:
public class QRDatabase
{
readonly SQLiteAsyncConnection _database;
public QRDatabase(string dbPath)
{
_database = new SQLiteAsyncConnection(dbPath);
_database.CreateTableAsync<db_QRCODE_Type>().Wait();
}
public Task<List<db_QRCODE_Type>> GetQRCode()
{
return _database.Table<db_QRCODE_Type>().ToListAsync();
}
public Task<int> SaveQRCode(db_QRCODE_Type note)
{
if (note.ID != 0)
{
return _database.UpdateAsync(note);
}
else
{
return _database.InsertAsync(note);
}
}
public Task<int> DelteQRCode(db_QRCODE_Type note)
{
return _database.DeleteAsync(note);
}
}
This uses this type:
public class db_QRCODE_Type
{
[PrimaryKey, AutoIncrement]
public int ID { get; set; } // Identificator of column
public string firstName { get; set; } // firstname
public string lastName { get; set; } // firstname
public byte[] qrBytes { get; set; } //qr code in bytes
}
Then, in the class where I need the DB I am doing this from the tutorial here:
https://learn.microsoft.com/de-de/xamarin/get-started/quickstarts/database?pivots=windows
static QRDatabase database;
static string nameOfDB = "01db_qrs_q2go.db3";
public static QRDatabase Database
{
get
{
if (database == null)
{
database = new QRDatabase(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), nameOfDB));
}
return database;
}
}
However, I am not quite sure how this works since I am never calling "Database" even though this is where the database is supposed to be initiliased.
Now, when I try to write to the database:
db_QRCODE_Type entry = new db_QRCODE_Type();
entry.firstName = entry_firstname.Text;
entry.lastName = entry_lastname.Text;
entry.qrBytes = qrCodeBytes;
try
{
await database.SaveQRCode(entry);
}
catch
{
DependencyService.Get<IMessage>().LongAlert("Etwas hat nicht funktioniert, bitte versuche es noch einmal. Fehlercode: DB_665h");
}
It fails saying it is not set reference to an instance and goes into the catch block. I am doing everything as in the tutorial. Why is this happening?
Thank you!