async void AlbumTappedAsync(object sender, ItemTappedEventArgs e)
{
var item = e.Item as Album;
var editPage = new PostListPage(new PostListViewModel(item));
await Navigation.PushAsync(editPage);
}
async void OpenPostList(object sender, EventArgs e)
{
var vm = BindingContext as AlbumViewModel;
var listPage = new PostListPage(new PostListViewModel(vm.CurrentAlbum));
await Navigation.PushAsync(listPage);
}