错误存在显式转换C＃，MVVM Light-LINQ

Question

I am learning MVVM Light and the app I am working on has a functionality to search for event names. Here are my codes for filtering a ListBox as the user types into TextBox . The error is: Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<NGO_Volunteer_Comm_Platform_v1._0.DataModel.Event>' to 'System.Collections.Generic.List<NGO_Volunteer_Comm_Platform_v1._0.DataModel.Event>'. An explicit conversion exists (are you missing a cast?) Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<NGO_Volunteer_Comm_Platform_v1._0.DataModel.Event>' to 'System.Collections.Generic.List<NGO_Volunteer_Comm_Platform_v1._0.DataModel.Event>'. An explicit conversion exists (are you missing a cast?)

ViewModel codes:

private static ObservableCollection<Event> _searchEventCollection = new ObservableCollection<Event>();

public static ObservableCollection<Event> SearchEventCollection
{
    get { return _searchEventCollection; }
    set { _searchEventCollection = value; }
}

//search from homepage event section
private RelayCommand _eventSearch;
/// <summary>
/// Gets the EventSearch.
/// </summary>
public RelayCommand EventSearch
{
    get
    {
        return _eventSearch
            ?? (_eventSearch = new RelayCommand(
            async () =>
            {
                SearchEventCollection.Clear();
                var eventList = await App.MobileService.GetTable<Event>().ToListAsync();

                foreach (Event ename in eventList)
                {
                    SearchEventCollection.Add(new Event
                    {
                        Id = ename.Id,
                        EventName = ename.EventName,
                        Date = ename.Date,
                        Location = ename.Location,
                        Desc = ename.Desc
                    });
                }
            }));
    }
}

private string filter;
public String Filter
{
    get
    {
        return this.filter;
    }
    set
    {
        this.filter = value;
        RaisePropertyChanged("SearchEventCollection");
    }
}
public List<Event> FilteredNames
{
    get
    {
        return (from name in SearchEventCollection where name.EventName.StartsWith(filter) select name);
    }
}        

public searchfromhomepageViewModel()
{
    filter = "";
}

How do I resolve this error?

Answer 1

Use the ToList extension method to create a List<T> from an IEnumerable<T> :

public List<Event> FilteredNames
{
    get
    {
        return (from name in SearchEventCollection where name.EventName.StartsWith(filter) select name).ToList();
    }
}

Or change the type of the FilteredNames property to IEnumerable<Event> . Actually, that's probably a better idea. In general, you shouldn't expose concrete collection types publicly, because it doesn't let you return an instance of a different type if you need to change it later. Also, returning a List<T> seems to imply that you can modify the list. But since a new list is returned each time the property is called, modifying it will have no effect on the property, so it's misleading.