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

[Mahdi Zareie]

Hi all
i'm scrutinizing Windows Forms ListBoxCollection 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.ObjectCollection.Add (object item)

and it will Call : System.Windows.Forms.ListBox.ObjectCollection.AddI nternal(object item)

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

and it will call : System.Windows.Forms.ListControl.GetItemText(objec t item)

and it will call : System.Windows.Forms.Formatter.FormatObject(object value, System.Type targetType, System.ComponentModel.TypeConverter sourceConverter, System.ComponentModel.TypeConverter targetConverter, string formatString, System.IFormatProvider formatInfo, object formattedNullValue, object dataSourceNullValue)

and it will call :System.Windows.Forms.Formatter.IsNullData(object value, object dataSourceNullValue)


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


which This Method Make My Equal Method too Run :

WindowsFormsApplication1.Student.Equals(object obj)


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