c# - 重用 XmlTextWriter 类

Question

是否可以重用 XmlTextWriter 类的同一个实例来生成更多的 xml 文档？我的意思是这样的:

XmlTextWriter writer = new XmlTextWriter();
writer.WriteStartDocument();
writer.WriteStartElement("Message1");
writer.WriteEndElement();
writer.WriteEndDocument();

// do something with xml created
...

writer.Reset() // ?
writer.WriteStartDocument();
writer.WriteStartElement("Message2");
writer.WriteEndElement();
writer.WriteEndDocument();
// do something with xml created
...

Answer 1

简单的回答:是的，这是可能的。

但如果底层流不指向文件，这将实现。 MemoryStream 就是一个很好的例子。

由于 MemoryStream 将流保存在“内存中”，您可以使用 XmlTextWriter 编写大量 XML 文件，并在结束每个文档后执行 MemoryStream.ToArray() 并将其作为 File.WriteAllBytes 的参数。

写入所有字节后，您将清除内存流。

您可以通过调用 MemoryStream.SetLength 方法清除内存流，并将长度设为 0:

• http://msdn.microsoft.com/en-us/library/system.io.memorystream.setlength.aspx

在此处阅读更多有关 XmlTextWriter 构造函数的流重载的信息:

• http://msdn.microsoft.com/en-us/library/ms162588.aspx

这对于 File.WriteAllBytes:

• http://msdn.microsoft.com/en-us/library/system.io.file.writeallbytes.aspx

关于重用XmlTextWriter

的一些问题

几年前@NigelTouch 对一些评论提出了担忧:

The problem I found is that if an exception is thrown part-way through, for example after WriteStartElement(), then even though you Flush() the Writer and set the Stream length to 0, the Writer remains in a WriteState of Element. When you start the next document, it begins with a closing ">" (for example). Avoid reuse

几个小时前，@Mike-EEE 遇到了同样的问题:

Please provide working code of an example solution. I am running into the same problem as Nigel describes

顺便说一句，一些试错让我恢复了给定的 XmlTextWriter 以根据需要多次重复使用它:

    using(MemoryStream stream = new MemoryStream())
    using(StreamReader streamReader = new StreamReader(stream))
    using(XmlTextWriter writer = new XmlTextWriter(stream, Encoding.UTF8))
    {
        writer.WriteStartDocument(true);
        writer.WriteStartElement("a");

        try 
        {
            throw new Exception();
        }
        catch 
        {
            // This line makes de magic: ending the document
            // avoids the issue mentioned by @NigelTouch
            writer.WriteEndDocument();
            writer.Flush();
            stream.SetLength(0);
        }


        writer.WriteStartDocument(true);
        writer.WriteStartElement("b");
        writer.WriteEndElement();
        writer.Flush();

        stream.Position = 0;

        Console.WriteLine(streamReader.ReadToEnd());

    }