Looking for right way to implement multiple properties dependency for binding in Xamarin View

Question

I'm new to Xamarin world, and its data binding rules. I have ViewModel with observable CurrentOrder property, and 3 properties which values depend on it. All 4 properties are used in View with bindings, so that each change in CurrentOrder should propagate changes to other 3 properties and that impact how view displays its controls and data. I'm confused with how I'm supposed to propagate the signal of CurrentOrder change to other 3 dependent properties. I came up with code that actually works, but to me it looks a bit awkward, and sets dependency inside independent property CurrentOrder, while I would prefer it to be other way around: dependent properties should better know what property they depend on.

Please note that SetProperty and OnPropertyChanged methods are in a base view model, and generated by standard VS Xamarin.Forms project pattern.

    private int _currentOrder = 1;
    public int CurrentOrder
    {
        get => _currentOrder;
        set => SetProperty(ref _currentOrder, value, onChanged: () =>
            {
                OnPropertyChanged(nameof(CurrentItem));
                OnPropertyChanged(nameof(IsTheLastItem));
                OnPropertyChanged(nameof(IsTheFirstItem));
            });

    }

    public string CurrentItem => Items[CurrentOrder - 1];

    public bool IsTheLastItem => CurrentOrder == Items.Count;

    public bool IsTheFirstItem => CurrentOrder == 1;

Any recommendations over best practices here are very appreciated

Answer 1

I would use Fody propertychanged for dependent properties like this.

Just add the nuget and dont forget to add FodyWeavers.xml, your class will be like below

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public int CurrentOrder {get; set;}
    public string CurrentItem => Items[CurrentOrder - 1];

    public bool IsTheLastItem => CurrentOrder == Items.Count;

    public bool IsTheFirstItem => CurrentOrder == 1;

}