Xamarin forms Back Button Navigation - xamarin.forms

Question

I'm working on a Xamarin Forms app and am using the MVVM Design.
the issue is when am navigating to another page using
Shell.Current.GoToAsync()
I disable the button to prevent Creating Multiple Pages or DB Operations.
but if I want to go back, I re-enable the buttons in the VM constructor, but the constructor never gets called which means the buttons are still disabled.
I tried to append the // in the Page route to remove the stack thinking that when I go back it will create a new instance Page and VM, but that did not work.
so can anyone help me resolving this problem.
thanks in advance.
Update:
VM Code
public RegisterViewModel()
{
Debug.WriteLine("Class Constructor", Class_Name);
//in case if disabled
RegisterButtonEnabled = true;
RegisterCommand = new Command(RegisterButtonOnClick);
}
public ICommand RegisterCommand { get; }
private bool registerButtonEnabled = true;
public bool RegisterButtonEnabled
{
get => registerButtonEnabled;
set
{
registerButtonEnabled = value;
OnPropertyChanged();
}
}
private async void RegisterButtonOnClick()
{
RegisterButtonEnabled = false;
//More Code
//and then go to Register Page
await Shell.Current.GoToAsync(nameof(RegisterPage));
}
and my xaml
<Button
Command="{Binding RegisterCommand}"
Text="{xct:Translate Register}"
Style="{StaticResource ButtonStyle}"
IsEnabled="{Binding RegisterButtonEnabled,Mode=OneWay}"/>

Answer 1

I had create a default shell project. And find something about the viewmodel. You can add the onappear and the ondisappear method to the viewmodel. Such as:
ViewModel:
public void OnAppearing()
{
RegisterButtonEnabled = true;
}
public void OnDisAppearing()
{
RegisterButtonEnabled = false;
}
Page.cs
ItemsViewModel _viewModel;
public ItemsPage()
{
InitializeComponent();
BindingContext = _viewModel = new ItemsViewModel();
}
protected override void OnAppearing()
{
base.OnAppearing();
_viewModel.OnAppearing();
}
protected override void OnDisappearing()
{
base.OnDisappearing();
_viewModel.OnDisAppearing();
}