Question

I stumbled across this very strange compiler behavior. I am trying to remove items from ObservableCollection based on some condition. Here is what I have in my code which throws error

public ObservableCollection<StandardContact> StandardContacts { get; set; }
....
StandardContacts.Remove(s => s.IsMarked); //Compiler Error

The error is as follows

Error Cannot convert lambda expression to type 'RelayAnalysis_Domain.Entity.StandardContact' because it is not a delegate type  

Surprisingly, the code below in the same method works

var deleteCount = StandardContacts.Where(s => s.IsMarked).Count(); //This Works

I already have following imports in my class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.Entity;

This question may turnout to be silly, but it has had my head scratching.

Note: Even the Intellisence shows the same error

Answer 1

As the error message unclearly states, you can’t do that.
ObservableCollection<T> does not have a method that removes items that match a condition. (unlike List<T>, which has RemoveAll())

Instead, you can loop backwards through the collection and call Remove().