Microsoft.VisualBasic.dll中发生了类型为'System.InvalidCastException'的第一次机会异常

Question

I'm working on converting some console code in a Microsoft sample for Dynamics CRM SDK 2011 to an ASP.NET web application. It runs fine in console mode, but after converting to run in ASP.NET I get the error:

A first chance exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll

Here is my source code:

    Public Sub Run(ByVal connectionString As String, ByVal promptforDelete As Boolean)
    Try
        Dim connection As Microsoft.Xrm.Client.CrmConnection =
            CrmConnection.Parse(connectionString)
        _orgService = New OrganizationService(connection)
        Using _orgService
            Dim account_Renamed As Account = New Account With {.Name = "Fourth Coffee"}
            _accountId = _orgService.Create(account_Renamed)
            Response.Write(CType("{0} {1}", Char()), account_Renamed.LogicalName, account_Renamed.Name)
            Dim cols As New ColumnSet(New String() {"name",
                                                   "address1_postalcode",
                                                    "lastusedincampaign"})
            Dim retrievedAccount As Account = _orgService.Retrieve("account", _accountId, cols).ToEntity(Of Account)()
            Response.Write("Retrieved record.")
            retrievedAccount.Address1_PostalCode = "98052"
            Response.Write("Updated Account Postal Code.")

        End Using
    Catch ex As Exception

    End Try
End Sub

Answer 1

So, I figured it out. In a web-based application there is no need to use {0} {1}:

Response.Write(CType("{0} {1}", Char()), account_Renamed.LogicalName, account_Renamed.Name)

Instead it can look like this:

Response.Write(account_Renamed.LogicalName & " " & account_Renamed.Name)

Answer 2

The reason that fails is not related to your application being web based. It has to do with how you're using CType() . You're using it to concatenate two strings which is not what it's used for.

The CType() method is used to cast an object to a particular type. With this snippet of code:

CType("{0} {1}", Char())

You're telling CType() to convert the string literal "{0} {1}" to a character array. Which actually works! Now you're passing a character array to Reponse.Write() along with two additional parameters which appear to be string values to me.

There is an overload of Reponse.Write() that accepts three arguments, the first being a character array but the other values are integers (index and count).

Honestly, I'm surprised this even built let alone ran. For future code, string concatenation is best done (IMHO) like so:

String.Format("{0} {1}", account_Renamed.LogicalName, account_Renamed.Name)

instead of concatenating with the & operator. If you concatenated the string in this manner, your code would change to this.

Response.Write(String.Format("{0} {1}", account_Renamed.LogicalName, account_Renamed.Name))

Using String.Format() is actually a shortcut way of using the StringBuilder class which is very efficient at string processing. When you use the concatenate operator, & , you create a completely new string object in memory every time a piece is attached to the string. StringBuilder creates/mutates strings in a mutable manner and is far faster when doing a lot of string work. That's why I consider it to be a best practice to use the shortcut method.