c# - MemoryStream、XmlTextWriter 和警告 4 CA2202 : Microsoft. 用法

Question

Visual Studio 2010 Ultimate 中的Run Code Analysis 命令在看到带有 MemoryStream 和 XmlTextWriter 的特定模式时返回警告。

这是警告:

Warning 7 CA2202 : Microsoft.Usage : Object 'ms' can be disposed more than once in method 'KinteWritePages.GetXPathDocument(DbConnection)'. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object.: Lines: 421 C:\Visual Studio 2010\Projects\Songhay.DataAccess.KinteWritePages\KinteWritePages.cs 421 Songhay.DataAccess.KinteWritePages

这是表格:

static XPathDocument GetXPathDocument(DbConnection connection)
{
    XPathDocument xpDoc = null;
    var ms = new MemoryStream();
    try
    {
        using(XmlTextWriter writer = new XmlTextWriter(ms, Encoding.UTF8))
        {
            using(DbDataReader reader = CommonReader.GetReader(connection, Resources.KinteRssSql))
            {

                writer.WriteStartDocument();
                writer.WriteStartElement("data");

                do
                {
                    while(reader.Read())
                    {
                        writer.WriteStartElement("item");
                        for(int i = 0; i < reader.FieldCount; i++)
                        {
                            writer.WriteRaw(String.Format("<{0}>{1}</{0}>", reader.GetName(i), reader[i].ToString()));
                        }
                        writer.WriteFullEndElement();
                    }

                } while(reader.NextResult());

                writer.WriteFullEndElement();
                writer.WriteEndDocument();

                writer.Flush();
                ms.Position = 0;

                xpDoc = new XPathDocument(ms);
            }
        }

    }
    finally
    {
        ms.Dispose();
    }

    return xpDoc;
}

此表单会产生相同类型的警告:

XPathDocument xpDoc = null;
using(var ms = new MemoryStream())
{
    using(XmlTextWriter writer = new XmlTextWriter(ms, Encoding.UTF8))
    {
        using(DbDataReader reader = CommonReader.GetReader(connection, Resources.KinteRssSql))
        {
            //...
        }
    }

}

return xpDoc;

顺便说一句，下面的表单会产生另一个警告:

XPathDocument xpDoc = null;
var ms = new MemoryStream();
using(XmlTextWriter writer = new XmlTextWriter(ms, Encoding.UTF8))
{
    using(DbDataReader reader = CommonReader.GetReader(connection, Resources.KinteRssSql))
    {
        //...
    }
}

return xpDoc;

以上产生警告:

Warning 7 CA2000 : Microsoft.Reliability : In method 'KinteWritePages.GetXPathDocument(DbConnection)', object 'ms' is not disposed along all exception paths. Call System.IDisposable.Dispose on object 'ms' before all references to it are out of scope. C:\Visual Studio 2010\Projects\Songhay.DataAccess.KinteWritePages\KinteWritePages.cs 383 Songhay.DataAccess.KinteWritePages

除了以下，我还有哪些选择？:

• 取消警告 CA2202。
• 抑制警告 CA2000 并希望微软正在处理MemoryStream(因为Reflector 没有向我显示源代码)。
• 重写我的遗留代码以识别精彩的 XDocument 和 LINQ toXML。

Answer 1

首先，永远不要使用 new XmlTextWriter()。自 .NET 2.0 以来，它已被弃用。请改用 XmlWriter.Create()。

其次，ms 的赋值应该在 using block 中:

using (var ms = new MemoryStream())
{
    using (var writer = XmlWriter.Create(ms))
    {
        // ...
    }
}

我相信警告是正确的。 MemoryStream 可以在释放 XmlTextWriter 时被释放，然后在“finally” block 中再次释放。