Question

I am simply trying to create an function to return a set of user. But, in order to be able to add the item later to a collection I used arrayList, but at last I am getting an error of Type ArrayList cannot be converted to 1-Dimensional array of Users

Here is my Code:

Function getDoctorsList() As Users()
    Dim userCollection As New ArrayList
    Dim sql = "SELECT * FROM '" + _tblName + "' WHERE usertype = 'doctor'"
    Dim dr As SqlDataReader = dbHelper.ExecuteAndGetReader(sql)
    While dr.Read
        Dim user As New Users
        user.Id = IIf(IsDBNull(dr("id")), 0, dr("id"))
        user.UserName = IIf(IsDBNull(dr("username")), "", dr("username"))
        user.UserNin = IIf(IsDBNull(dr("user_nin")), 0, dr("user_nin"))
        user.UserType = IIf(IsDBNull(dr("usertype")), "", dr("usertype"))
        user.Password = IIf(IsDBNull(dr("password")), "", dr("password"))
        userCollection.Add(user)
    End While
    Return userCollection
End Function

How to solve such problems?

Answer 1

Either let your method return an ArrayList:

Function getDoctorsList() As ArrayList()

create an Array out of your ArrayList:

Return userCollection.ToArray()

or, the best solution, let your method return an IEnumerable(Of User)

Function getDoctorsList() As IEnumerable(Of User)

you should also use a List(of User) instead of a ArrayList instead, since it is type safe (and clearer) and it also implements IEnumerable(Of User).

---

Edit

Example using IEnumerable(of Users) and DataRowExtensions:

Function GetDoctorsList() As IEnumerable(of Users)
    Dim sql = "SELECT * FROM '" + _tblName + "' WHERE usertype = 'doctor'"
    Dim table = new DataTable()
    table.Load(dbHelper.ExecuteAndGetReader(sql))
    Return (from row in table.AsEnumerable()
            select new User() With
            {
               .Id = row.FieldOf(Of Integer)("id"),
               .UserName = row.Field(Of String)("username"),
               .UserNin = row.Field(Of Integer)("user_nin"),
               .UserType = row.Field(Of String)("usertype"),
               .Password = row.Field(Of String)("password")
            }).ToList()
End Function