Silverlight在读取器关闭时无效尝试调用FieldCount

Question

我使用stored procedure call创建了一个包含两个参数的IDataReader。当我尝试读取值时，它会引发Invalid attempt to call FieldCount when reader is closed.错误。我不是closing the connection也不是using。我不知道为什么我会收到这个错误。在immediate window我没有看到reader.HasRows属性，但是当我调试时，我可以在拨打电话时看到结果，但是当我想要阅读它时，它会抛出错误。

代码：

public bool UniqueColumnValuesCheckCall(ObservableCollection<String> selectedColumns, String selectedTableName)
{
    bool uniqueValueExists = true;
    String columns = String.Empty;
    String result = String.Empty;

    if (selectedColumns != null && selectedColumns.Count > 0)
        columns = String.Join(", ", selectedColumns);

    int commandTimeout = GetSQLCommandTimeOut();
    IDataParameter[] parameters = 
    {   
        this.Helper.GetParameter("@columnName", columns),
        this.Helper.GetParameter("@tableName", selectedTableName)
    };

    //I can see results while debugging.
    IDataReader reader = this.Helper.WithCommandTimeout(commandTimeout).ExecuteReader(this.ConnectionString, "IX_FindUniqueColumnValues", parameters);

    try
    {
        while (reader.Read()) // For some reason it throws error "Invalid attempt to call FieldCount when reader is closed." here
        {
            if (!reader.IsDBNull(0))
                result = reader.GetString(0);

            if (result.Equals("Selected columns have no unique values"))
                uniqueValueExists = false;
            else
                uniqueValueExists = true;
        }
    }
    catch (Exception)
    {
        throw;
    }

    return uniqueValueExists;
}