/// <summary>
/// Attaches a child <see cref="IViewModel"/> to a parent <see cref="IViewModel"/>.
/// If the child has already been attached, the newer instance will be attached instead of the previous instance.
/// By being attached, the child will be disposed when the parent is disposed.
/// Both also share the same <see cref="IViewModelView"/>.
/// </summary>
/// <remarks>The previous instance will be disposed when replaced.</remarks>
/// <param name="viewModel">The parent <see cref="IViewModel"/>.</param>
/// <param name="childViewModel">The child <see cref="IViewModel"/> to detach.</param>
/// <param name="name">The child ViewModel's name. This defaults to <paramref name="childViewModel"/>.Name when not provided.</param>
public static TChildViewModel AttachOrReplaceChild <TChildViewModel>(this IViewModel viewModel, TChildViewModel childViewModel, string name = null)
where TChildViewModel : IViewModel
{
name = name ?? childViewModel.Name;
if (viewModel.TryGetDisposable(name, out var instance))
{
viewModel.DetachChild((IViewModel)instance, name);
instance.Dispose();
}
return(viewModel.AttachChild(childViewModel, name));
}
/// <summary>
/// Gets the child of this <see cref="IViewModel"/> for the specified <paramref name="name"/>.
/// If the child doesn't exist, it is created and attached using <paramref name="childViewModelProvider"/>.
/// </summary>
/// <typeparam name="TChildViewModel">The type of child ViewModel.</typeparam>
/// <param name="viewModel">The parent <see cref="IViewModel"/>.</param>
/// <param name="childViewModelProvider">The factory to the child <see cref="IViewModel"/>.</param>
/// <param name="name">The child ViewModel's name.</param>
/// <returns>The attached child <see cref="IViewModel"/>. Default of <typeparamref name="TChildViewModel"/> is returned if the <see cref="IViewModel"/> is disposed.</returns>
public static TChildViewModel GetChild <TChildViewModel>(
this IViewModel viewModel,
Func <TChildViewModel> childViewModelProvider,
[CallerMemberName] string name = null
) where TChildViewModel : IViewModel
{
if (viewModel.IsDisposed)
{
return(default(TChildViewModel));
}
if (!viewModel.TryGetDisposable <TChildViewModel>(name, out var childViewModel))
{
childViewModel = viewModel.AttachChild(childViewModelProvider(), name);
}
return(childViewModel);
}