It is my xaml file:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:mojaapkamobilna="clr-namespace:MojaApkaMobilna" x:DataType="mojaapkamobilna:MainViewModel"
         x:Class="MojaApkaMobilna.MainPage">
<StackLayout>
    <Label x:Name="TopLabel" Text="{Binding TopText}"></Label>
    <StackLayout Orientation="Horizontal">
        <Label VerticalOptions="Center">Imie:</Label>
        <Entry x:Name="Name" Placeholder="Wpisz swoje imię" WidthRequest="300" Text="{Binding Name}"></Entry>
    </StackLayout>
    <StackLayout Orientation="Horizontal">
        <Label VerticalOptions="Center">Haslo:</Label>
        <Entry x:Name="Password" Placeholder ="Wpisz swoje hasło" IsPassword="True" WidthRequest="300" Text="{Binding Password}"></Entry>
    </StackLayout>
    <Button Text="Kliknij we mnie..." Command = "{Binding OnClickCommand}"></Button>

    <ScrollView>
        <CollectionView ItemsSource="{Binding Persons}">
            <CollectionView.ItemTemplate>
               <DataTemplate>
                   <StackLayout>
                       <Label FontSize="20"  Text="{Binding Name}" />
                        <Label FontSize="20" Text="{Binding Password}"></Label>
                   </StackLayout>
               </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>
    </ScrollView>
    <Button></Button>
</StackLayout>

And it's my xaml.cs file:

namespace MojaApkaMobilna
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
            BindingContext = new MainViewModel();
        }
    }
}

And my view model class:

 namespace MojaApkaMobilna
{
    internal class MainViewModel : INotifyPropertyChanged
    {
        private string _name;
        private string _password;
        private string _topText;

        public ObservableCollection<Person> Persons { get; } = new ObservableCollection<Person>();

        public string TopText
        {
            get => _topText;
            set
            {
                _topText = value;
                OnPropertyChanged(nameof(TopText));
            }
        }
        public string Name
        {
            get => _name;
            set
            {
                _name = value;
                OnPropertyChanged(nameof(Name));
                OnClickCommand.ChangeCanExecute();
            }
        }
        public string Password
        {
            get => _password;
            set
            {
                _password = value;
                OnPropertyChanged(nameof(Password));
                OnClickCommand.ChangeCanExecute();
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        public Command OnClickCommand { get; }

        private void Button_Clicked()
        {
            TopText = "Wpisane imie: "   Name   ", Haslo: "   Password;

            try
            {
                Persons.Add(new Person(Name, Password));
                foreach (var person in Persons)
                {
                    Console.WriteLine(person.Name);
                    Console.WriteLine(person.Password);
                }

                Console.WriteLine(Persons.Count);
            }
            catch
            {
                TopText = "Nie powiódł się zapis nowego użytkownika";
            }
        }

        public MainViewModel()
        {
            OnClickCommand = new Command(Button_Clicked, Validate);

        }


        /* Informowanie widoku o zmianach */
        private void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

        private bool Validate() => !string.IsNullOrWhiteSpace(Name) && !string.IsNullOrWhiteSpace(Password);
        
    }
}

And my problem is that my scroolview doesnt work. Interesting is that when program is running, when I delete that ItemsSource (xaml file) and write it again, it starts working. Why is it happening and how to repair it?

 <CollectionView ItemsSource="{Binding Persons}">

I'm weak in Xamarin, so thank you for your understanding.

CodePudding user response：

I found solution. In AssemblyInfo file:

[assembly: XamlCompilation(XamlCompilationOptions.Compile)]

replace by:

[assembly: XamlCompilation(XamlCompilationOptions.Skip)]