How do i add record from data table - sqlite

Question

I would add record to my table with a form to fill out, but there is a error from ListerPF()
"Object reference not set to an instance of an object"
Here is the whole process:
await App.methode.AddNewPF(Label_NumeroNF.Text, DatePicker_Date.Date, Editor_LibelleNF.Text, Picker_TypeFrais.SelectedItem.ToString(), double.Parse(Entry_Quantite.Text), double.Parse(Entry_Tarif.Text), double.Parse(Entry_Montant.Text), double.Parse(Entry_MontantTotal.Text), CheckBox_CCEntreprise.IsChecked, int.Parse(Entry_Imputation.Text));
Navigation.PushAsync(new PostesNF());
And the code behind "AddNewPF" is:
public async Task AddNewPF(string numero , DateTime date, string libelle, string typeFrais, double quantite, double tarif, double montant, double montantTotal, bool carteCredit, int imputationCC)
{
int result = 0;
try
{
result = await connection.InsertAsync(new DB_PosteNF { Numero = numero, Date = date, Libelle = libelle, TypeFrais = typeFrais, Quantite = quantite, Tarif = tarif, Montant = montant, MontantTotal = montantTotal, CarteCredit = carteCredit, ImputationCC = imputationCC});
StatutMessage = $"{result} poste de frais ajouté : {numero} | {typeFrais} ";
}
catch (Exception ex)
{
StatutMessage = $"Impossible d'ajouter le poste de frais avec le numéro: {numero}. \nErreur : {ex.Message}";
}
}
When the "PosteNF" page appears, I have this code
protected override async void OnAppearing()
{
base.OnAppearing();
CollectionViewPF.ItemsSource = await App.methode.ListerPF();
}
the problematic code "ListerPF" is:
public async Task<List<DB_PosteNF>> ListerPF(DB_ListeNF datareceived)
{
try
{
string numero = datareceived.Numero;
//return await connection.Table<DB_PosteNF>().ToListAsync();
return await connection.Table<DB_PosteNF>().Where(x => x.Numero == numero).ToListAsync();
}
catch (Exception ex)
{
StatutMessage = $"Impossible d'afficher la liste des postes de frais. \nErreur : {ex.Message}";
}
return new List<DB_PosteNF>();
}
But when I go back to the "PostesNF" page, the registered data is not displayed. Thanks for your help !

Answer 1

Per your code snippets, the model is DB_PosteNF with 10 properties.The key is that when you retrieve the records from the data table, I think you need a ObservableCollection<DB_PosteNF> to receive these entities that read from the database.Below is the code snippets for your reference:
First, define a UserCollection using ObservableCollection
public ObservableCollection<User> UserCollection { get; set; }
Then, in OnAppearing method:
protected override async void OnAppearing()
{
base.OnAppearing();
UserDB db = await UserDB.Instance;
List<User> a = await db.GetUserAsync();
UserCollection = new ObservableCollection<User>(a);
userinfodata.ItemsSource = UserCollection;
}
PS: In my case, the mode is User.