Use of task to prepare a XmlDocument from a file with WinRT library functions.

Question

I was wondering if there is a better way to write a function that reads an XML file and turns it into a XmlDocument object, and then executes a user specified function on that XmlDocument.  Not feeling too expert, I did come up with one solution, but would like an expert opinion on that solution, and also if there is a better way?

void FileIo::getXML( std::function< void ( Windows::Data::Xml::Dom::XmlDocument ^ passedDoc ) >  myXmlDocHandler )
{
	using namespace Windows::Storage;
	using namespace Windows::Storage::Pickers;
	using namespace Windows::Data::Xml::Dom;
	using namespace concurrency;

	auto picker= ref new FileOpenPicker();
   	picker->FileTypeFilter->Append(".xml");	// Required 
	task< StorageFile^ > getFileTask ( picker->PickSingleFileAsync() ); 

	getFileTask.then([ myXmlDocHandler ]( StorageFile^ xmlFile ) 
	{
		if ( xmlFile != nullptr) 
		{ 
			auto doc= ref new XmlDocument();	
			task< XmlDocument ^ > getDocTask ( doc->LoadFromFileAsync( xmlFile ) ); 
			getDocTask.then( [ myXmlDocHandler ] ( XmlDocument^ doc ) 
			{	
				myXmlDocHandler( doc );
			});
		}
	});

}


//--------------------------------------

// Calling mechanism

	auto lambda = []( Windows::Data::Xml::Dom::XmlDocument ^ xmlDoc ) 
			{
				// Now go process the XML file as you like
				Platform::String ^ nodeName= xmlDoc->NodeName;
			};

	FileIo::getXML(	lambda );

The full context is at:

http://social.msdn.microsoft.com/Forums/en-US/winappswithnativecode/thread/66df8021-6f3e-429c-83b8-392ddc737194

Answer 1

Hi, Andrew,

The code you pasted looks correct to me. For Yashpal_S 's question on that ref thread, there is an alternative api interface which returns a task of XmlDocument^ instread of asking user passing in an callback function.

The Pseudocode could be something like this:

concurrency::task<Windows::Data::Xml::Dom::XmlDocument> FileIo::getXML()
{
	using namespace Windows::Storage;
	using namespace Windows::Storage::Pickers;
	using namespace Windows::Data::Xml::Dom;
	using namespace concurrency;

	auto picker= ref new FileOpenPicker();
   	picker->FileTypeFilter->Append(".xml");	// Required 
	return create_task(picker->PickSingleFileAsync()).then([]( StorageFile^ xmlFile ) 
	{
		if ( xmlFile == nullptr)
		    cancel_current_task(); // abort current task and its continuations
        
		auto doc= ref new XmlDocument();
		return doc->LoadFromFileAsync( xmlFile ); 
	})
}

// -------------------call it
FileIo::getXML().then([](Windows::Data::Xml::Dom::XmlDocument doc) {
    // do whatever you want.
});

Hong