Question

雖然它似乎是一個非常微不足道的問題，但我試圖理解XMLReader類，它是成員。鑑於我想退出打印XML聲明

static void Main(string[] args) 
    { 
      StringBuilder output = new StringBuilder(); 

      String xmlString = 
        @"<?xml version='1.0'?> 
    <!-- This is a sample XML document --> 
    <Items> 
     <Item>test with a child element <more/> stuff</Item> 
    </Items>"; 
      // Create an XmlReader 
      using (XmlReader reader = XmlReader.Create(new StringReader(xmlString))) 
      { 
       XmlWriterSettings ws = new XmlWriterSettings(); 
       ws.Indent = true; 
       using (XmlWriter writer = XmlWriter.Create(output, ws)) 
       { 

        // Parse the file and display each of the nodes. 
        while (reader.Read()) 
        { 
         switch (reader.NodeType) 
         { 
          case XmlNodeType.Element: 
           writer.WriteStartElement(reader.Name); 
           break; 
          case XmlNodeType.Text: 
           writer.WriteString(reader.Value); 
           break; 
          case XmlNodeType.XmlDeclaration: 
          case XmlNodeType.ProcessingInstruction: 
           writer.WriteProcessingInstruction(reader.Name, reader.Value); 
           break; 
          case XmlNodeType.Comment: 
           writer.WriteComment(reader.Value); 
           break; 
          case XmlNodeType.EndElement: 
           writer.WriteFullEndElement(); 
           break; 
         } 
        } 

       } 
      } 
      Console.WriteLine(output.ToString()); 
      Console.ReadKey(); 
     } 

的XML文件，但如果我註釋掉

case XmlNodeType.XmlDeclaration: 
           case XmlNodeType.ProcessingInstruction: 
            writer.WriteProcessingInstruction(reader.Name, reader.Value); 
            break; 

我仍然能看到XML聲明即

<?xml version='1.0'?> 

什麼問題這裏 ？ 再次，如果我註釋掉

case XmlNodeType.Element: 
writer.WriteStartElement(reader.Name); 
break; 

它說InvalidOperationException異常是未處理的。 你能解釋一下嗎？我沒有得到全部的圖片。

Answer 1

該聲明的寫作是XmlWriter的一項功能。您可以使用XmlWriterSettings退出此選項。

var settings = new XmlWriterSettings 
{ 
    OmitXmlDeclaration = true 
}; 

using (XmlWriter writer = XmlWriter.Create(output, settings)) 

爲所有可用設置的完整詳情，請參閱the documentation。

Answer 2

在您的代碼中設置ws.OmitXmlDeclaration = true;以省略xml聲明。

static void Main(string[] args) 
{ 
     StringBuilder output = new StringBuilder(); 

     String xmlString = 
       @"<?xml version='1.0'?> 
<!-- This is a sample XML document --> 
<Items> 
    <Item>test with a child element <more/> stuff</Item> 
</Items>"; 
     // Create an XmlReader 
     using (XmlReader reader = XmlReader.Create(new StringReader(xmlString))) 
     { 
      XmlWriterSettings ws = new XmlWriterSettings(); 
      ws.OmitXmlDeclaration = true; 
      ws.Indent = true; 
      using (XmlWriter writer = XmlWriter.Create(output, ws)) 
      { 

       // Parse the file and display each of the nodes. 
       while (reader.Read()) 
       { 
        switch (reader.NodeType) 
        { 
         case XmlNodeType.Element: 
          writer.WriteStartElement(reader.Name); 
          break; 
         case XmlNodeType.Text: 
          writer.WriteString(reader.Value); 
          break; 
         //case XmlNodeType.XmlDeclaration: 
         case XmlNodeType.ProcessingInstruction: 
          writer.WriteProcessingInstruction(reader.Name, reader.Value); 
          break; 
         case XmlNodeType.Comment: 
          writer.WriteComment(reader.Value); 
          break; 
         case XmlNodeType.EndElement: 
          writer.WriteFullEndElement(); 
          break; 
        } 
       } 

      } 
     } 
     Console.WriteLine(output.ToString()); 
     Console.ReadKey(); 
    }