An implementation of INotifyPropertyChanged that provides SetProperty method that triggers the PropertyChanged event.

SetProperty performs equality checking and is overloaded for many types to avoid boxing It includes an optional argument for providing multiple dependent properties that will change at the same time.

Additionally returns a bool indicating whether the value was actually changed.

public class PersonViewModel : NotifyPropertyChangedBase
{
    private string _firstName;
    public string FirstName
    {
        get => _firstName;
        set => SetProperty(ref _firstName, value, otherProperties: nameof(FullName));
    }

    private string _lastName;
    public string LastName
    {
        get => _lastName;
        set => SetProperty(ref _lastName, value, otherProperties: nameof(FullName));
    }

    public string FullName => $"{FirstName} {LastName}";

    private string _telephoneNumber;
    public string TelephoneNumber
    {
        get => _telephoneNumber;
        set
        {
            if (SetProperty(ref _telephoneNumber, value))
            {
                ValidateTelephoneNumber();
            }
        }
    }

    public void ValidateTelephoneNumber()
    {
        ...
    }
}

All the following assume you have something like the following in your XAML:

xmlns:gwg="clr-namespace:GamesWithGravitas.XamarinForms.Layout;assembly=GamesWithGravitas.XamarinForms.Layout"

A pair of attached properties that allow databinding the children of any Layout.

<StackLayout gwg:Layout.ItemsSource="{Binding People}">
    <gwg:Layout.ItemTemplate>
        <DataTemplate>
            <StackLayout>
                <Label Text="{Binding FirstName}"/>
                <Label Text="{Binding LastName}"/>
            </StakLayout>
        </DataTemplate>
    </gwg:Layout.ItemTemplate>
</StackLayout>

A Layout that arranges all its children on top of each other. Each child is laid out with the size of the largest.

<gwg:LayerLayout>
    <Image Source="my_background" />
    <Text Label="Overload text" />
</gwg:LayerLayout>

A Layout that behaves like a horizontal StackLayout, arranging children one after the other until they can no longer fit. Additional children are then placed on a new row.

Each child will get at least the size it requests. If the child has HorizontalOptions set to include Expand it will be given more space in the same way it would when used in a StackLayout. Each child is given height equal to to the tallest child on the same row.

Example coming soon.

A Layout that behaves like WrapLayout, except all children are the same width (Expand is ignored).

Example coming soon.

A Layout that behaves like Grid, except all cells are square. It will attempt to give every child the same space as the largest child.

Example coming soon.

Docs coming soon.

Docs coming soon.