Create a Data-Driven Messaging System: C# & VB: Check Exception Types: Listing 3

Based on the Exception type, the GetMessage() method can return specific messages based on the exception itself. One of the more common uses is to override the SqlException messages with one that is more descriptive in the context of the application. For example, when checking for a foreign key error at a specific place in an application, you could return something descriptive such as: "You can not delete orders when order detail records exists." That kind of message is far better for users than something like: "The DELETE statement conflicted with the REFERENCE constraint "FK_Order_Details_Orders". The conflict occurred in database "Northwind", table "dbo.Order Details", column 'OrderID'. The statement has been terminated."

// C#
public string GetMessage( 
  Exception ex, string ClassName)
{
  mstrClassName = ClassName;
  mLastException = ex;

  switch (mLastException.GetType().ToString())
  {
    case "System.Data.SqlClient.SqlException":
      foreach (SqlError sqlex in 
               ((SqlException)mLastException).Errors)
      {
        mstrMessage = this.GetMessage(mstrClassName,
          "SqlException", sqlex.Number, Int32.MinValue);
        if (mstrMessage != string.Empty)
          break;
      }
      break;
    default:
       mstrMessage = 
         Me.GetMessage(mstrClassName,
         mLastException.GetType().ToString());
      break;
  }

  // Did not get a message, use the default
  if (mstrMessage == string.Empty)
    mstrMessage = mstrDefaultMessage;
  return mstrMessage;
}

' VB.NET
Public Function GetMessage( _
  ByVal ex As Exception, _
  ByVal ClassName As String) As String
  mstrClassName = ClassName
  mLastException = ex

  Select Case mLastException.GetType().ToString()
    Case "System.Data.SqlClient.SqlException"
      Dim sqlex As SqlError
      For Each sqlex In CType(mLastException, _
        SqlException).Errors
        mstrMessage = Me.GetMessage( _
          mstrClassName, _
         "SqlException", sqlex.Number, Int32.MinValue)
        If mstrMessage <> String.Empty Then
          Exit For
        End If
      Next
    Case Else
       mstrMessage = Me.GetMessage(mstrClassName, _
         mLastException.GetType().ToString())
  End Select

  ' Did not get a message, use the default
  If mstrMessage = String.Empty Then
    mstrMessage = mstrDefaultMessage
  End If
  Return mstrMessage
End Function
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