Suggestion: Make history public or some GetPreviousViewModel method

[AlexanderSjo]

Hi! Thanks for an amazing and simple to use library!

I miss a simple feature to get the history. Or mainly the previous ViewModel. My use case is that I want to put Focus on a certain Button depending on where the user previously was.

Do you think this could be done?

[sandreas]

You maybe could use:

// check history if there was a previous item
if(_router.HasPrev) {
    var lastViewModel = _router.Back(); // go back to last ViewModel
    _router.Forward();
}

But this would create an unwanted transition, so you are right... the history is something I could at least make protected or even public (readonly). I'll try to integrate this into the next version.

Maybe I'm gonna use something like this in addition:

// optional: Add a GoTo with a delegate
_router.GoTo(history => history.ElementAt(0));

// optional: get history item by index.
var previousItem = _router.GetHistoryItem(-1);

However, the HistoryRouter is so simple, you could just to copy and paste it (e.g. MyHistoryRouter) to solve this temporarily for your use case:

public class MyHistoryRouter<TViewModelBase>: Router<TViewModelBase> where TViewModelBase: class
{
    
    private int _historyIndex = -1;
    private List<TViewModelBase> _history = new();
    private readonly uint _historyMaxSize = 100;

    public bool HasNext => _history.Count > 0 && _historyIndex < _history.Count - 1;
    public bool HasPrev => _historyIndex > 0;
    
    // HERE IS THE NEW PROPERTY
    public List<TViewModelBase> History => _history.AsReadOnly();


    public MyHistoryRouter(Func<Type, TViewModelBase> createViewModel) : base(createViewModel)
    {
    }
    
    public void Push(TViewModelBase item)
    {
        if (HasNext)
        {
            _history = _history.Take(_historyIndex + 1).ToList();
        }
        _history.Add(item);
        _historyIndex = _history.Count - 1;
        if (_history.Count > _historyMaxSize)
        {
            _history.RemoveAt(0);
        }
    }
    
    public TViewModelBase? Go(int offset = 0)
    {
        if (offset == 0)
        {
            return default;
        }

        var newIndex = _historyIndex + offset;
        if (newIndex < 0 || newIndex > _history.Count - 1)
        {
            return default;
        }
        _historyIndex = newIndex;
        var viewModel = _history.ElementAt(_historyIndex);
        CurrentViewModel = viewModel;
        return viewModel;
    }
    
    public TViewModelBase? Back() => HasPrev ? Go(-1) : default;
    
    public TViewModelBase? Forward() => HasNext ? Go(1) : default;
    
    public override T GoTo<T>()
    {
        var destination = InstantiateViewModel<T>();
        CurrentViewModel = destination;
        Push(destination);
        return destination;
    }
}

[AlexanderSjo]

Amazing, thank you! I will be using a modified HistoryRouter for now.