PR12/Prak12/ViewModels/MainWindowViewModel.cs

using Avalonia.Controls;
using ReactiveUI;

namespace Prak12.ViewModels
{
    public class MainWindowViewModel : ViewModelBase
    {
        public MainWindowViewModel()
        {
            ShowTeachersViewModel stvm = new ShowTeachersViewModel();
            stvm.ButtonAddNewTeacherWasPressed += ButtonAddNewTeacherWasPressed;
            UserControl = (new ViewLocator()).Build(stvm);
        }

        private void ButtonAddNewTeacherWasPressed()
        {
            AddTeachersViewModel atvm = new AddTeachersViewModel();
            atvm.AddNewTeacherPageWasClosed += AddNewTeacherPageWasClosed;
            UserControl = (new ViewLocator()).Build(atvm);
        }

        private void AddNewTeacherPageWasClosed()
        {
            ShowTeachersViewModel stvm = new ShowTeachersViewModel();
            stvm.ButtonAddNewTeacherWasPressed += ButtonAddNewTeacherWasPressed;
            UserControl = (new ViewLocator()).Build(stvm);
        }

        public Control UserControl
        {
            get => _userControl;
            set => this.RaiseAndSetIfChanged(ref _userControl, value);
        }


        private Control _userControl;
    }
}