Load only few items in ListView, but make all the items available to search in the CollectionView filter

Question

I have a ListView that needs to display a ton of rows (think about 40,000+) and have a Filter implemented through a Textbox, where the user can search and find the item in the ListView. But I would like to display only a few rows (around 1000) in the listview , but make the entire 40,000+ rows searchable through the filter.
It doesn't make any sense to me to display all 40,000 rows which takes a lot of time to load and render in UI. I would rather show only a few rows to start with and have the user search for what they need.

Here's what I have for the code to implement ListView with Filter.

XAML:

ViewModel:

public CollectionViewSource viewSource;

    public ObservableCollection emailList = new ObservableCollection();

    public ObservableCollection EmailList
    {
        get { return emailList; }
        set
        {
            if (value != emailList)
            {
                emailList = value;
                emailSelected = null;
                OnPropertyChanged("EmailLIst");
            }
        }
    }
    private string ldapFilter;

    public string LdapFilter
    {
        get { return ldapFilter; }
        set
        {
            if (value != ldapFilter)
            {
                ldapFilter = value;
                this.viewSource.View.Refresh();
                //FilterResults();
                OnPropertyChanged("LdapFilter");
            }
        }
    }

Model:

public class Person
{
    public int ID { get; set; }
    public string EmailId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

Accepted Answer

I update your ViewModel to let the ListView show specified items when the query condition is null.

public class ViewMode  
    {  
        public ViewModel()  
        {  
            maxShowItems = 20;  
  
            for (int i=0;i<40000;i++)  
            {  
                EmailList.Add(new Person() { ID = i, FirstName = "Rose"+i.ToString(), LastName = "Bob", EmailId = "132165410@ss.com" });  
            }  
  
            PersonListView = new ListCollectionView(EmailList);  
            PersonListView.Filter += Filter;  
  
        }  
  
  
        private bool Filter(object obj)  
        {  
            Person person = obj as Person;  
            if (person == null) return false;  
  
            if (PersonListView.Count > maxShowItems && string.IsNullOrEmpty(ldapFilter))  
            {  
                if (person.ID < maxShowItems)  
                {  
                    return true;  
                }  
                return false;  
            }  
  
  
            if (string.IsNullOrEmpty(ldapFilter))  
            {  
                return true;  
            }  
            else  
            {  
                if (person.FirstName.Contains(ldapFilter))  
                {  
                    return true;  
                }  
                return false;  
            }  
        }  
  
        public ListCollectionView PersonListView { get; set; }  
  
        public ObservableCollection emailList = new ObservableCollection();  
  
        public ObservableCollection EmailList  
        {  
            get { return emailList; }  
            set  
            {  
                if (value != emailList)  
                {  
                    emailList = value;  
                    OnPropertyChanged("EmailLIst");  
                }  
            }  
        }  
  
  
        private string ldapFilter;  
        public string LdapFilter  
        {  
            get { return ldapFilter; }  
            set  
            {  
                if (value != ldapFilter)  
                {  
                    ldapFilter = value;  
                    this.PersonListView.Refresh();  
                    //FilterResults();  
                    OnPropertyChanged("LdapFilter");  
                }  
            }  
        }  
  
  
        private int maxShowItems;  
        public int MaxShowItems  
        {  
            get { return maxShowItems; }  
            set  
            {  
                if (value != maxShowItems)  
                {  
                    maxShowItems = value;  
                    this.PersonListView.Refresh();  
                    OnPropertyChanged("MaxShowItems");  
                }  
            }  
        }  
    }

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Answer

Thank you @DaisyTian-MSFT . That worked

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Load only few items in ListView, but make all the items available to search in the CollectionView filter

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