How to setup my bindingcontext for my xamarin.forms app with mvvm and sqlite - xamarin

Question

The basic of my app is that i have an AgendaPage which has a collectionview of items and when i click the add icon, i can fill a form to populate this collectionview.
My app was working when i didn't set my app MVVM style but i am trying to apply the MVVM logic to my app.
Currently if i set the BindingContext of my NewFormPage to Agenda() my NewFormPage opens when i click the add button BUT if i set my BindingContext to NewFormViewModel, nothing open up and my app crash so i am trying to figure out what i am doing wrong in setting up this MVVM.
Note: currently i only have a clicked function to open up the page ( didn't implement the command yet, i was trying to implement the save command).
Agenda.cs in the database folder
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Text;
using SQLite;
using Calculette.Database;
namespace Calculette.Models
{
[Table("Agenda")]
public class Agenda
{
[PrimaryKey, AutoIncrement]
public int ID { get; set; }
public string Topic { get; set; }
public string Duration { get; set; }
public DateTime Date { get; set; }
}
}
NewFormViewModel.cs in the ViewModel folder
using Calculette.Database;
using Calculette.Models;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
using Xamarin.Forms;
namespace Calculette.ViewModel
{
class NewFormViewModel : BaseViewModel
{
public Command AgendaSaveFormCommand { get; set; }
public NewFormViewModel()
{
AgendaSaveFormCommand = new Command(async () => await SaveForm(), () => !IsBusy);
}
public string Topic
{
get => Topic;
set
{
Topic = value;
NotifyPropertyChanged();
}
}
public string Duration
{
get => Duration;
set
{
Duration = value;
NotifyPropertyChanged();
}
}
public DateTime Date
{
get => Date;
set
{
Date = value;
NotifyPropertyChanged();
}
}
bool isBusy = false;
public bool IsBusy
{
get { return isBusy; }
set
{
isBusy = value;
//OnPropertyChanged();
AgendaSaveFormCommand.ChangeCanExecute();
}
}
public int ID { get; }
async Task SaveForm()
{
IsBusy = true;
await Task.Delay(4000);
IsBusy = false;
Agenda agenda = new Agenda();
await App.Database.SaveAgendaAsync(agenda);
await Application.Current.MainPage.DisplayAlert("Save", "La tâche a été enregistrée", "OK");
}
}
}
NewFormPage.xaml.cs in the Views folder
using Calculette.Models;
using Calculette.ViewModel;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
namespace Calculette.Views
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class NewFormPage : ContentPage
{
public NewFormPage ()
{
InitializeComponent ();
// BindingContext = new Agenda();
BindingContext = new NewFormViewModel();
}
}
}
AgendaPage.xaml in the views folder (xaml that calls Clicked that open NewFormPage
<ImageButton Source="iconplus.png" HeightRequest="30" WidthRequest="30" Clicked="GoToNewFormPage"></ImageButton>
the GoToNewFormPage function in AgendaPage.xaml.cs
protected async void GoToNewFormPage(object sender, EventArgs e)
{
await Navigation.PushAsync(new Views.NewFormPage());
}

Answer 1

You did not set value for the object's property when clicking on the add icon.
async Task SaveForm()
{
IsBusy = true;
await Task.Delay(4000);
IsBusy = false;
Agenda agenda = new Agenda();
//here you should set value of a blank object
Agenda.Topic = xx;
Agenda.Date = xx;
Agenda.Duration = xx;
await App.Database.SaveAgendaAsync(agenda);
await Application.Current.MainPage.DisplayAlert("Save", "La tâche a été enregistrée", "OK");
}

Answer 2

all of your properties are implemented incorrectly
this will lead to an infinite recursive loop - Duration will call Duration will call Duration... until your app crashes
public string Duration
{
// this will just call the capital-D Duration property again
// which will then call itself again, and again, and again
get => Duration;
set
{
// this will call the setter for the capital-D Duration property recursively
Duration = value;
NotifyPropertyChanged();
}
}
you need to have a private backing field that is named differently than the property
private string duration;
public string Duration
{
get => duration;
set
{
duration = value;
NotifyPropertyChanged();
}
}