Running Device Emulator in XP Mode

If the frustration of VS2008 corrupting some of the VS2005 SDKs isn't enough to burn your butt, it's just a warm-up exercise to getting the Device Emulator working in Windows 7's XP Mode.

The first month of isolating VS2008 and VS2005 by installing one of them into XP Mode Virtual PC (VPC) was certainly disappointing. VS2008 didn't want to cooperate at all. So I did the next best thing: installed VS2005 there instead. It was a long and boring process to get VS2005, its service packs and a bunch of SDKs installed, but it worked without much pain. It even compiled some code. But launching a device emulator was a different story.

On connecting to the Mobile 5 Pocket PC Emulator device, which I use regularly for testing, the computer just stared blankly at me for a few minutes before declaring:

Cannot connect to device. Error: 0x8007064a

Try a web search for that. Mwa-hah-ha!

Anyway, the short story and the two-part solution. I finally found some obscure and easily overlooked references from people who had similar experiences.


Part One. Visual Studio won't open the project.

1. Open the solution. Visual Studio complains: "The project file cannot be loaded. The application for project ... is not installed.". Shutting down VS and restarting does nothing.


2. Right-click the project (which offers no information about why it fails. Other than some stupid message about "platform not available" or something moronically insulting like that. It's all BS - the SDKs are installed.


3. Select Reload project.


4. Watch with anger and puzzlement as VS loads the project correctly this time. Shoot me.

Part Two. The device emulator fails when running in XP Mode. I followed Brian Peek's useful guide to replacing the missing Microsoft network adapter, Windows Virtual PC and the Microsoft Device Emulator, which may have helped solved other future problems. For the emulator error, the article Cannot connect to device. Error: 0x8007064a was helpful.

1. Launch the emulator by trying to connect or by executing in with or without debugging. VS complains: "Cannot connect to device. Error: 0x8007064a".


2. Terminate the Device Emulator Manager.


3. Rename the Folder "CoreCon" (in "Documents and Settings\Application Data\Microsoft\") to "xCoreCon".


4. Start the Device Emulator (list of devices is now empty).


5. Terminate the Device Emulator.


6. Rename "xCoreCon" back to "CoreCon".


7. Now the emulator works. Shoot me and the computer.

Is Microsoft running the US Congress? Maybe that's the problem. Well, at least Solitaire still works.

XML Default Namespaces and XPath Queries

The use of namespaces in XML schemas are useful and even necessary, but they cause a lot of confusion! This is compounded (confounded?) by the XPath API having different rules for applying namespaces than the rules applied to documents.

The biggest confusion for me came from the use of the default namespace. Use of a default namespace simplifies writing an XML document because it limits or eliminates the need to prefix element and attribute names. However, it places a bigger burden on the reader because the use of any namespace mandates the additional requirement of using a namespace manager in the API calls when executing queries. Any namespace that may be used in the document must be added to the namespace manager's map, including the default namespace. Be aware that the default namespace is not the same as no namespace, which is a vitally important principle of XPath queries.

Additionally, the query itself must include a namespace prefix for any and every element to be parsed. Regardless if the XML document qualifies the element to identify the namespace or not, the XPath query must qualify the elements. An unqualified element in the query will search the "no namespace" or "null" namespace, not the default namespace; XPath has no concept of a default namespace. This short blurb is found in the Microsoft documentation: XPath treats the empty prefix as the null namespace. So if your schema specifies a target namespace, an unqualified query element will never match anything in it.

What's the solution? Here are two.

1. Remove all namespaces from your XML document. For simple documents you don't plan on validating, this may be an acceptable alternative. But it's probably not a good idea for complex documents or documents where the construction will be validated; in these cases, the use of namespaces is almost mandated.

Sample XML document with no namespaces:

<?xml version="1.0" encoding="utf-8"?>
<parent>
  <child id="1">
    <item>Item 1</item>
    <item>Item 2</item>
  </child>
</parent>

Sample reader code:

use System.Xml;

XmlDocument doc = new XmlDocument();
doc.Load("/hasnodefault.xml");

// Query some elements. This is what you would naturally expect.
// Namespace prefixes cannot be used in these queries.
XmlNode root = doc.SelectSingleNode("/parent");
foreach (XmlNode node in root.SelectNodes("child/item"))
{
  // Do something with the child items.
  ;
}

2. Use a namespace manager when you are parsing your documents. If you use a default namespace, you must map it to some prefix (something other than an empty string); I will often use "default", which makes it obvious where I'm looking. Your XPath queries, unfortunately, will necessarily be more complicated, as you will have to include the namespace prefix on all elements you will be querying.

Sample XML document using a default namespace (xmlns=...):

<?xml version="1.0" encoding="utf-8"?>
<parent xmlns="http://tempuri.org/sample.xsd">
  <child id="1">
    <item>Item 1</item>
    <item>Item 2</item>
  </child>
</parent>

Sample reader code:

use System.Xml;

XmlDocument doc = new XmlDocument();
doc.Load("/hasdefault.xml");
XmlNamespaceManager nsmanager = new XmlNamespaceManager(doc.NameTable);

// Map the default namespace. Not optional.
// Note that the namespace URI is significant, not the prefix.
nsmanager.AddNamespace("default", "http://tempuri.org/sample.xsd");

// Query some elements.
// The namespace prefixes are required or the query will return null.
XmlNode root = doc.SelectSingleNode("/default:parent", nsmanager);
foreach (XmlNode node in root.SelectNodes("default:child/default:item", nsmanager))
{
  // Do something with the child items.
  ;
}

The short version of this story is: if you use namespaces in your document, even if it is a default namespace, you must qualify the elements used in your XPath queries and use a namespace manager with them.

Obviously, things can get more complicated than these simple examples. Understanding these fundamental concepts about namespaces is critical to maintaining your sanity.

For .NET users new to XML, the XPath queries (a W3C standard for addressing parts of XML documents) are implemented by the .NET framework's XmlNode.SelectNodes() and XmlNode.SelectSingleNode() methods and their related counterparts built on XPathNavigator and XPathExpression classes.

More information about XPath 1.0 is available at http://www.w3.org/TR/xpath.