How to check if byte is null vb.net

Question

I'm assigning background images to every button according to my SQL Server database. If a byte is null I get this error:

Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.

I want to allow buttons with no background images, but the error is preventing me.

Here is what I attempted:

Dim strsql As String
Dim ImgSql() As Byte

Using con As New SqlConnection("constring")
    con.Open()
    strsql = "SELECT Imagen FROM Inventario WHERE ID=@ID"
    Dim cmd As New SqlCommand(strsql, con)
    ItemID = 1
    cmd.Parameters.Add("@ID", SqlDbType.VarChar).Value = ItemID
    Dim myreader As SqlDataReader

    myreader = cmd.ExecuteReader
    myreader.Read()
    ImgSql = myreader("Imagen")
    If ImgSql IsNot Nothing AndAlso ImgSql.Length > 0 Then

        Dim ms As New MemoryStream(ImgSql)
        btn1.BackgroundImage = Image.FromStream(ms)
        con.Close()
    Else
        'do nothing
    End If
End Using

@JoelCoehoorn whoops thanks for pointing that out. I have a bad habit to VarChar everything. — jumexmango
– jumexmango, Commented Sep 28, 2021 at 15:38
@djv I know its NULL, the point is to allow it to be NULL and still be able to run the program. — jumexmango
– jumexmango, Commented Sep 28, 2021 at 16:24

Joel Coehoorn · Accepted Answer · 2023-10-11 14:11:03Z

2

Public Function GetImage(ID As Integer) As Image
    Dim sql As String = "SELECT Imagen FROM Inventario WHERE ID=@ID"
    Using con As New SqlConnection("constring"), _
          cmd As New SqlCommand(sql, con)

        cmd.Parameters.Add("@ID", SqlDbType.Integer).Value = ID
        con.Open()
        Using myreader As SqlDataReader = cmd.ExecuteReader()
            If myreader.Read() AndAlso Not DBNull.Value.Equals(myreader("Imagen")) Then
                Dim ImgSql() As Byte = DirectCast(myreader("Imagen"), Byte())         
                Using ms As New MemoryStream(ImgSql)
                     Return Image.FromStream(ms)
                End Using
            End If
         End Using
    End Using
End Function

' ...

btn1.BackgroundImage = GetImage(1)

edited Oct 11, 2023 at 14:11

answered Sep 27, 2021 at 21:14

Joel Coehoorn

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djv · Accepted Answer · 2021-09-27 20:51:47Z

1

Based on this answer in C#, converted to vb.net and added NULL check

Using con As New SqlConnection("constring")
    Using cmd = con.CreateCommand()
        cmd.CommandText = "SELECT Imagen FROM Inventario WHERE ID=@ID"
        Dim ItemID = 1
        cmd.Parameters.AddWithValue("@ID", ItemID)
        con.Open()
        Dim res = cmd.ExecuteScalar()
        If res IsNot Nothing Then
            ImgSql = CType(res, Byte())
            If ImgSql IsNot Nothing AndAlso ImgSql.Length > 0 Then
                Dim ms As New MemoryStream(ImgSql)
                btn1.BackgroundImage = Image.FromStream(ms)
            End If
        End If
    End Using
End Using

answered Sep 27, 2021 at 20:51

djv

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