When overridden in a derived class, writes the XML declaration with the version "1.0".
Assemblies: System.Xml.ReaderWriter (in System.Xml.ReaderWriter.dll)
System.Xml (in System.Xml.dll)
This is not the first write method called after the constructor.
An XmlWriter method was called before a previous asynchronous operation finished. In this case, InvalidOperationException is thrown with the message “An asynchronous operation is already in progress.”
The encoding level of the document is determined by how the writer is implemented. For example, if an Encoding object is specified in the XmlTextWriter constructor, this determines the value of the encoding attribute. This method does not create a standalone attribute.
When WriteStartDocument is called the writer validates that what you are writing is a well-formed XML document. For example, it checks that the XML declaration is the first node, that one and only one root-level element exists, and so on. If this method is not called, the writer assumes an XML fragment is being written and applies no root level rules.
If WriteStartDocument has been called and then the WriteProcessingInstruction method is used to create another XML declaration, an exception will be thrown.
For the asynchronous version of this method, see WriteStartDocumentAsync.
.NET FrameworkSupported in: 4.6, 4, 3.5, 3.0, 2.0, 1.1, 1.0
.NET Framework Client ProfileSupported in: 4, 3.5 SP1
Portable Class LibrarySupported in: Portable Class Library
.NET for Windows Store appsSupported in: Windows 8
Supported in: Windows Phone 8.1
Supported in: Windows Phone Silverlight 8.1
Supported in: Windows Phone Silverlight 8
Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.