Hello San,
You haven't provided enough information, but it's likely due to you not setting your BindingContext correctly, thus the RadListView's ItemsSource is null. I've written you a demo, attached.
For your convenience, here is the code:
namespace SelectedItemsOnPageLoad.Portable
{
public partial class StartPage : ContentPage
{
private ObservableCollection<BaseListClass> _items;
private ObservableCollection<BaseListClass> selectedInstances = new ObservableCollection<BaseListClass>();
public StartPage()
{
InitializeComponent();
}
private void Handle_SelectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
}
protected override void OnAppearing()
{
base.OnAppearing();
IsBusy = true;
LoadData();
IsBusy = false;
foreach (var selectedInstance in selectedInstances)
{
var instanceInItemsList = Items.FirstOrDefault(item => item.Name == selectedInstance.Name);
listView.SelectedItems.Add(instanceInItemsList);
}
}
public ObservableCollection<BaseListClass> Items
{
get => _items ?? (_items = new ObservableCollection<BaseListClass>());
set
{
_items = value;
OnPropertyChanged();
}
}
void LoadData()
{
var list = Enumerable.Range(1, 20).Select(i => new BaseListClass
{
Name = $"Item {i}"
});
foreach (var item in list)
{
Items.Add(item);
}
// adding some of the items to selected items collection
selectedInstances.Add(Items[1]);
selectedInstances.Add(Items[3]);
selectedInstances.Add(Items[4]);
}
}
public class BaseListClass
{
public string Name { get; set; }
}
}
Note that I removed the await operator from the call on LoadData. Your shared code is not compilable as LoadData is not marked async. Additionally, you should never use async void unless it's top level event handler.
I've attached a runnable demo for you to see this in action at runtime:
Regards,
Lance | Tech Support Engineer, Sr.
Progress Telerik
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