Adding member to list overides previous members - vb.net

Question

I need to read from an Excel file a list of dogs with their birth date, and store them in a list. The read works well, and every time I add a new dog to the list, the list count grows. So far so good.
The problem is that when I add the 2nd record, the first record is replaced by the first record content, so I have two identical records. And so on with every new record. In the end, I have many same records - all with the value of the last dog.
The dog class is:
Public Class DogClass
Public Name As String
Public Dob As Date
Public Age As Integer
Public Sex As String
Public Sub setDogName(ByVal _name As String)
Name = _name
End Sub
Public Sub setDogDOB(ByVal _dob As Date)
Dob = _dob
End Sub
Public Sub setDogAge(ByVal _age As String)
Age = _age
End Sub
Public Sub setDogSex(ByVal _sex As String)
Sex = _sex
End Sub
End Class
The class of the list is:
Public Class DogsListClass
Public dogsList As New List(Of DogClass)
Public Function DodgsCnt() As Integer
DodgsCnt = dogsList.Count()
End Function
Public Function DogExsists(_dogName As String) As Boolean
Dim res As Boolean = False
For Each item As DogClass In dogsList
If item.Name = _dogName Then
res = True
End If
Next
Return res
End Function
Public Sub AddDog(_dog As DogClass)
dogsList.Add(_dog)
End Sub
End Class
The calling:
Dim tdog As New DogClass
Dim DogsList As New DogsListClass
Do
tdog.setDogName(MyExcel.Cells(row_cnt, col_cnt).text)
tdog.setDogDOB(MyExcel.Cells(row_cnt, col_cnt + 1).value)
DogsList.AddDog(tdog)
Loop
Any idea why the records are being overridden?

Answer 1

DogsList variable must be declared outside the Do...Loop, otherwise you are creating a "New" DogsList at each iteration and, based on this code, you should end up having one single item in the collection, not many.
Also, declaring DogsList in the loop, prevents you from using it outside in the rest of your code.