why listbox1.Items.Add use Equals Method of my Object ?

[Mahdi Zareie]

Hi all
i'm scrutinizing Windows Forms ListBoxCollecti on Add Method,
during the analyzing i found that the method "add" calls Equals method in base Object
why this method do this action ?

[Mahdi Zareie]

I Have used "Call Stack" and I have Find This Answer :

We Call :System.Windows .Forms.ListBox. ObjectCollectio n.Add(object item)

and it will Call : System.Windows. Forms.ListBox.O bjectCollection .AddInternal(ob ject item)

and it will Call : System.Windows. Forms.ListBox.N ativeAdd(object item)

and it will call : System.Windows. Forms.ListContr ol.GetItemText( object item)

and it will call : System.Windows. Forms.Formatter .FormatObject(o bject value, System.Type targetType, System.Componen tModel.TypeConv erter sourceConverter , System.Componen tModel.TypeConv erter targetConverter , string formatString, System.IFormatP rovider formatInfo, object formattedNullVa lue, object dataSourceNullV alue)

and it will call :System.Windows .Forms.Formatte r.IsNullData(ob ject value, object dataSourceNullV alue)


and Finally it will call : object.Equals(o bject objA, object objB)


which This Method Make My Equal Method too Run :

WindowsFormsApp lication1.Stude nt.Equals(objec t obj)


and The Last Parameter which Will be Send to My Equals Method (as obj) is a DBNULL Object !
what is a DBNULL ?