Question

I have a class that implements IDataReader and the needed functions are written, but I get an error message stating

Class ‘CSVDataReader’ must implement ‘Function GetBoolean(i As Integer) As Boolean’ for interface ‘System.Data.IDataRecord’.

IDataReader has many functions and properties. How do I implement the functions without rewriting them all?

Here is my class

    Public Class CSVDataReader
    Implements IDataReader
    Private stream As StreamReader
    Private columnsByName As New Dictionary(Of String, Integer)()
    Private columnsByOrdinal As New Dictionary(Of Integer, String)()
    Private currentRow As String()
    Private _isClosed As Boolean = True

    Public Sub New(fileName As String)
        If Not File.Exists(fileName) Then
            Throw New Exception("File [" & fileName & "] does not exist.")
        End If

        Me.stream = New StreamReader(fileName)

        Dim headers As String() = stream.ReadLine().Split(",")
        For i As Integer = 0 To headers.Length - 1
            columnsByName.Add(headers(i), i)
            columnsByOrdinal.Add(i, headers(i))
        Next

        _isClosed = False
    End Sub

    Public Sub Close()
        If stream IsNot Nothing Then
            stream.Close()
        End If
        _isClosed = True
    End Sub

    Public ReadOnly Property FieldCount() As Integer
        Get
            Return columnsByName.Count
        End Get
    End Property

    ''' <summary>
    ''' This is the main function that does the work - it reads in the next line of data and parses the values into ordinals.
    ''' </summary>
    ''' <returns>A value indicating whether the EOF was reached or not.</returns>
    Public Function Read() As Boolean
        If stream Is Nothing Then
            Return False
        End If
        If stream.EndOfStream Then
            Return False
        End If

        currentRow = stream.ReadLine().Split(",")
        Return True
    End Function

    Public Function GetValue(i As Integer) As Object
        Return currentRow(i)
    End Function

    Public Function GetName(i As Integer) As String
        Return columnsByOrdinal(i)
    End Function

    Public Function GetOrdinal(name As String) As Integer
        Return columnsByName(name)
    End Function

    Public Function GetOrdinal(name As String) As Integer
        Return columnsByName(name)
    End Function
End Class

Answer 1

You have to implement all the methods and properties.

An interface is a contract – if an object says it can provide the services listed on the interface, it has to provide all of them. An interface is not a base class – there is no “template” code to fall back on if you don’t implement something.

It’s OK not to put any code in the methods/properties you aren’t interested in (I usually put Throw New NotImplementedException so I know when I’ve inadvertently called a method I wasn’t planning to). But the stubs have to be there.