NameDialogViewModel.cs

using System;
using Prism.Commands;
using Prism.Dialogs;

namespace PrismSample.ViewModels
{
    public class NameDialogViewModel : BaseViewModel, IDialogAware
    {
        public NameDialogViewModel()
        {
            SubmitCommand = new DelegateCommand(OnSubmitTapped);
        }

        private string _name;
        public string Name
        {
            get => _name;
            set => SetProperty(ref _name, value);
        }

        public DelegateCommand SubmitCommand { get; }

        private void OnSubmitTapped()
        {
            RequestClose(new DialogParameters { { "Name", Name } });
        }

        public event Action<IDialogParameters> RequestClose;

        public bool CanCloseDialog() => true;

        public void OnDialogClosed() { }

        public void OnDialogOpened(IDialogParameters parameters) { }
    }
}