Android Question HEX number/string check

Dim Test As String
Dim BadHex As Boolean

Test = "0Dabcde12345678"

For I = 0 To Test.Length - 1

    If Asc(Test.ToUpperCase.SubString2(I, I + 1)) > 70 OR Asc(Test.ToUpperCase.SubString2(I, I + 1)) < 48 Then
				
       BadHex = True

    End If

Next

If BadHex = True Then

   Msgbox("Bad Hex number", "")
			
Else

   Msgbox("OK", "")
			
End If

Sub HexToLong(HexStr As String) As Long
    Dim Lng As Long
    Dim Digit As String
    Dim DigitVal As Int

    For I = HexStr.Length -1 To 0 Step -1
        Digit = HexStr.SubString2(I, I+1).ToUpperCase
        If Not("0123456789ABCDEF".Contains(Digit)) Then
            ' not valid char
            Return -1
        End If

        If Digit.CompareTo("9") > 0 Then
            DigitVal = Asc(Digit) - 55
        Else
            DigitVal = Digit
        End If
        Lng = Lng + DigitVal * Power(16, HexStr.Length - 1 - I)
    Next

    Return Lng
End Sub