如何修复 CA2202 警告

public static String PrintXML(String XML)
    {
        String result = "";
        string[] xmlSeperators = new string[] { "<?" };
        string[] splitResults = new string[2];
        if (!String.IsNullOrEmpty(XML))
        {
            using (MemoryStream mStream = new MemoryStream())
            {
                using (XmlTextWriter writer = new XmlTextWriter(mStream, Encoding.Unicode))
                {
                    XmlDocument document = new XmlDocument();
                    try
                    {
                        // Load the XmlDocument with the XML.
                        //Check if it is only XML 
                        if (XML.StartsWith("<?"))
                        {
                            document.LoadXml(XML);
                        }
                        else
                        {
                            //Split the string appended before XML
                            splitResults = XML.Split(xmlSeperators, 2, StringSplitOptions.None);
                            if (splitResults.Length > 1)
                            {
                                string d = "<?" + splitResults[1];
                                document.LoadXml(d);
                            }
                        }
                        writer.Formatting = Formatting.Indented;
                        // Write the XML into a formatting XmlTextWriter
                        document.WriteContentTo(writer);
                        //xx.WriteTo(writer);
                        writer.Flush();
                        mStream.Flush();
                        // Have to rewind the MemoryStream in order to read its contents.
                        mStream.Position = 0;
                        // Read MemoryStream contents into a StreamReader.
                        StreamReader sReader = new StreamReader(mStream);
                        // Extract the text from the StreamReader.
                        String FormattedXML = sReader.ReadToEnd();
                        if (splitResults[0] != null)
                        {
                            result = splitResults[0] + "'n" + FormattedXML;
                        }
                        else
                        {
                            result = FormattedXML;
                        }
                    }
                    catch (XmlException xe)
                    {
                        Log.Error(xe);
                        throw;
                    }                        
                }                   
            }
        }
        return result;
    }

收到此警告的原因是XmlTextWriter.Dispose()将确保下躺的MemoryStream对象也被释放。因此，当MemoryStream的using范围结束时，它将尝试释放MemoryStream对象，从而释放警告。

using块编译为try-finally块。代码中的内部using块将在writer上调用Dispose。这将调用MemoryStream对象mStream上的Dispose。在从内部 using 块退出控件时，外部 using 块将尝试释放对象writer，但由于它已被释放，因此在代码分析工具上收到警告。

要消除警告，您可以删除第一个using语句并使用try-finally块。但请记住，在输入第二个using语句后立即将mStream设置为null。CA2202 中对此进行了解释：不要多次释放对象

您的代码如下所示：

public static String PrintXML(String XML)
{
    String result = "";
    string[] xmlSeperators = new string[] { "<?" };
    string[] splitResults = new string[2];
    if (!String.IsNullOrEmpty(XML))
    {
        MemoryStream mStream  = null;
        try
        {
            mStream = new MemoryStream();
            using (XmlTextWriter writer = new XmlTextWriter(mStream, Encoding.Unicode))
            {
                mStream = null; // important 
                XmlDocument document = new XmlDocument();
                try
                {
                    // Load the XmlDocument with the XML.
                    //Check if it is only XML 
                    if (XML.StartsWith("<?"))
                    {
                        document.LoadXml(XML);
                    }
                    else
                    {
                        //Split the string appended before XML
                        splitResults = XML.Split(xmlSeperators, 2, StringSplitOptions.None);
                        if (splitResults.Length > 1)
                        {
                            string d = "<?" + splitResults[1];
                            document.LoadXml(d);
                        }
                    }
                    writer.Formatting = System.Xml.Formatting.Indented;
                    // Write the XML into a formatting XmlTextWriter
                    document.WriteContentTo(writer);
                    //xx.WriteTo(writer);
                    writer.Flush();
                    mStream.Flush();
                    // Have to rewind the MemoryStream in order to read its contents.
                    mStream.Position = 0;
                    // Read MemoryStream contents into a StreamReader.
                    StreamReader sReader = new StreamReader(mStream);
                    // Extract the text from the StreamReader.
                    String FormattedXML = sReader.ReadToEnd();
                    if (splitResults[0] != null)
                    {
                        result = splitResults[0] + "'n" + FormattedXML;
                    }
                    else
                    {
                        result = FormattedXML;
                    }
                }
                catch (XmlException xe)
                {
                    Log.Error(xe);
                    throw;
                }
            }
        }
        finally 
        {
            if (mStream != null)
            {
                mStream.Dispose();
            }
        }
    }
    return result;
}

您可以像另一个答案所说的那样抑制错误警告，但消除此问题的实际方法是仅在代码中实际调用一次 .Dispose() 方法，并且仅在完成使用它之后调用它。如果再次释放已释放的对象，则会引发 System.ObjectDisposedException 异常，但不确定。可以在对象上多次调用正确的 dispose 方法，并且不会/可能不会为您生成错误。但不能保证这样做。

Microsoft的开发人员网络文档已对此进行了说明，

若要解决与此规则的冲突，请更改实现，以便无论代码路径如何，都只对对象调用一次 Dispose。

更多： http://msdn.microsoft.com/en-us/library/ms182334.aspx

当您嵌套了using语句，其中内部语句包含外部语句中的资源时，会发生这种情况。在这种情况下，XmlTextWriter将在处置MemoryStream时对其进行处置，然后外部using语句将导致第二次处置它。

您可以通过将外部using语句替换为 try/finally 来手动释放内存流：

MemoryStream mStream = null;
try
{
    mStream = new MemoryStream();
    using (XmlTextWriter writer = new XmlTextWriter(mStream, Encoding.Unicode))
    {
      mStream = null;
     ...
    }
}
finally
{
    if(mStream != null)
        mStream.Dispose();
}

(见 http://msdn.microsoft.com/en-us/library/ms182334.aspx(