Question

I filled some ObservableCollection<Employe> collection:

// Program.Data.Employees - it is ObservableCollection<Employe>.
Program.Data.Employees.Add(new Employe() { Name="Roman", Patronymic="Petrovich", Surname="Ivanov" });
Program.Data.Employees.Add(new Employe() { Name = "Oleg", Patronymic = "Vladimirovich", Surname = "Trofimov" });
Program.Data.Employees.Add(new Employe() { Name = "Anton", Patronymic = "Igorevich", Surname = "Kuznetcov" });

In other place of my code I try to remove some item from this collection:

// Program.Data.Employees - it is ObservableCollection<Employe>.
Employe x = Program.Data.Employees.First(n => n.Guid == emp.Guid); // x is not null.
Int32 index = Program.Data.Employees.IndexOf(x); // I got -1. Why?
Boolean result = Program.Data.Employees.Remove(x); // I got 'false', and item is not removed. Why?
// But this works fine:
Program.Data.Employees.Clear();

I can clear collection, but I can’t remove necessary item. Why it happens?

UPD: Equals method of my Employe class

public bool Equals(Employe other) {
    return
    other.Guid == this.Guid &&
    String.Equals(other.Name, this.Name, StringComparison.CurrentCultureIgnoreCase) &&
    String.Equals(other.Patronymic == this.Patronymic, StringComparison.CurrentCultureIgnoreCase) &&
    String.Equals(other.Surname == this.Surname, StringComparison.CurrentCultureIgnoreCase) &&
    other.Sex == this.Sex &&
    String.Equals(other.Post == this.Post, StringComparison.CurrentCultureIgnoreCase);
}

Answer 1

I tried the following code to reproduce your error:

class Employee
{
  public string Name { get; set; }
  public Guid Guid { get; set; }
}

// ...
ObservableCollection<Employee> employees = new ObservableCollection<Employee>();
var guid1 = Guid.NewGuid();
employees.Add(new Employee { Name = "Roman", Guid = guid1 });
employees.Add(new Employee { Name = "Oleg", Guid = Guid.NewGuid() });

var x = employees.First(e => e.Guid == guid1);
var index = employees.IndexOf(x); // index = 0, as expected
var result = employees.Remove(x); // result = true, as expected

It worked as expected. I would suggest, you set a breakpont at var x = ... and check, if

• The collection really contains the item you’re looking
• If First() really returns that item

Then go to the next line and check, if index is returned correctly. And finally check again, if result is really false.

I see several possible causes of your code failing:

• You didn’t post the full code and something happens between x=Program.Data.Employees.First() and Program.Data.Employees.IndexOf()
• You use multithreaded code (which also results in “something happening” between the two statements). In this case, you need to synchronize the access to the collection
• You don’t use a ObservableCollection directly but some derived class instead which is constructed by your data layer (such as DataServiceCollection, but this one should work fine too). In this case, check the actual type of your collection in the debugger

Another typical cause of errors with collection would be, if you try to remove items while iterating over the collection (i.e. inside a foreachloop): but in this case an exception should be thrown (and IndexOf should work fine), so this would only apply if you use some derived class which implements non-standard behaviour.

EDIT (in return to you posting your Equal method)

Your Equal method has a serious error in it:

String.Equals(other.Patronymic == this.Patronymic, StringComparison.CurrentCultureIgnoreCase)
... // applies also for following comparisons

should be

String.Equals(other.Patronymic, this.Patronymic, StringComparison.CurrentCultureIgnoreCase)
...

Also, if you’re using a Guid, consider only comparing the GUIDs, since this usually means ‘unique identifier’, so it should be enough to identify some entity.