Why does my property from my viewmodel get reset everytime I change the page?

See more:

C#

WPF

MVVM

DataContext

I have this Property:

private string _TextBox1 = "Input";
        public string TextBox1
        {
            get
            {
                return _TextBox1;
            }
            set
            {
                _TextBox1 = value;

                NotifyPropertyChanged(nameof(TextBox1));
            }
        }

I placed it like that:

Text="{Binding TextBox1, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"

Now I type in some text and Change with that to next Page in my Project:

PagesNavigation.Navigate(new System.Uri("/EttiketPage.xaml", UriKind.RelativeOrAbsolute));

But now the Text I wrote get erased and the normal "Input" line is back.

What I have tried:

I know the ViewModel creates more then one Instance which it could be erased. To avoid that I created an ApplicationService class with that:

public sealed class ApplicationService
    {
        private ApplicationService() { }

        public static ApplicationService Instance { get; } = new ApplicationService();

        public ViewModel PrintView { get; } = new ViewModel();
    }

And in every Page I placed this DataContext:

DataContext="{Binding PrintView, Source={x:Static local:ApplicationService.Instance}}"

But for some reason the data of the Property get erased every time I change the Page, someone an Idea?