Re: Getting the volume names of disks - C# Discussion Boards

13-Feb-05 6:16

Hello!

I want to get the volume names of the disks on my computer. I found a nice way that you are supposed to be able to get it and this is the way:

<br />
			SelectQuery sqlLogicalDrives = new SelectQuery("SELECT * FROM Win32_LogicalDisk");<br />
			ManagementObjectSearcher moSearcher = new ManagementObjectSearcher(sqlLogicalDrives);<br />
			ManagementObjectCollection mocLogicalDrives = moSearcher.Get();<br />
<br />
			foreach (ManagementObject moDrive in mocLogicalDrives)<br />
			{<br />
				cmbExplorerRootFolder.Items.Add(moDrive.Properties["VolumeName"].Value.ToString());<br />
			}<br />

but for some reaseon I get the error message: An unhandled exception of type 'System.NullReferenceException' occurred in MyProject.exe

Anyone who can tell me what I'm doing wrong?

Thanks in advance!

~~~~~~~~~~~~~~
Martin Lundberg
Student, Sweden

I have to thank every member of the Code Project for making it such a great place for a beginner to learn!

Heath Stewart13-Feb-05 6:56

13-Feb-05 6:56

Either the value returned by Properties["VolumeName"] or .Value is null. You need to do some simple checks from unknown sources beforing calling methods or accessing properties on an instance:

foreach (...)
{
  PropertyData data = moDrive.Properties["VolumeName"];
  if (data != null)
  {
    object value = data.Value;
    if (value != null)
      cmbExplorerRootFolder.Items.Add(value.ToString());
  }
}

You can actually simplify this code, however, using the indexer for the ManagementObject class that gets the value or a property as its proper type:

foreach (...)
{
  string value = moDrive["VolumeName"] as string;
  if (value != null)
    cmbExplorerRootFolder.Items.Add(value);
}

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Marlun13-Feb-05 8:08

13-Feb-05 8:08

Hello again!

Now the error is not showed (thanks! =)) but, nothing is added to the combobox =/. When the application starts I can hear a: (the floppy drive) but it is not added to the combobox and neither is anything else =/

~~~~~~~~~~~~~~
Martin Lundberg
Student, Sweden

I have to thank every member of the Code Project for making it such a great place for a beginner to learn!

Marlun13-Feb-05 8:16

13-Feb-05 8:16

Found out why, I had not named my disks, but still in Explorer they look like: Local Disk (C Smile | :)

, Local Disk (D Smile | :)

, etc.

Should I get what kind of disk it is, and then if volume is empty add like Local disk, myself or is local disk something else then "VolumeName"? =)

Thanks in advance!

~~~~~~~~~~~~~~
Martin Lundberg
Student, Sweden

I have to thank every member of the Code Project for making it such a great place for a beginner to learn!

Heath Stewart13-Feb-05 21:38

13-Feb-05 21:38

You'd best get the drive letter and optionally get the name. What you see by default in Explorer is the drive type.

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Marlun14-Feb-05 1:29

14-Feb-05 1:29

Hello!

But the DriveType I get by using ["DriveType"] is an int meaning different stuff like: 2 = Removable disk, 3 = local disk, 5 = compact disk. In Explorer it diferences from CD and DVD. I've got a swedish version of winXP so I'm not really sure what it says in the english ones.

~~~~~~~~~~~~~~
Martin Lundberg
Student, Sweden

I have to thank every member of the Code Project for making it such a great place for a beginner to learn!

Heath Stewart14-Feb-05 7:59

14-Feb-05 7:59

Your subject reads "Getting the volume names of disks", so why do you care about the drive types? To accurately get the drive types you should be using a different set of APIs that encapsulate getting the drive type based on what media is in there. These require P/Invoke and can be found in the "Windows Management" section of the Platform SDK, available for download or you can find the documentation online at http://msdn.microsoft.com/library[^].

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Marlun14-Feb-05 18:56

14-Feb-05 18:56

Sorry that I was confused from start (and still am). I thought that what I saw was the Volume names. I've been trying to find the Windows Management and P/Invoke section. I've found the Windows Management Instrumentation (WMI) but still not P/Invoke or how to get the srive types. I'll search some more, thanks once again for the help! =)

Edit: I found something here: http://www.dotnet247.com/247reference/msgs/19/99154.aspx I have not tested it yet but it uses P/Invoke so it may be what your talking about.

~~~~~~~~~~~~~~
Martin Lundberg
Student, Sweden

I have to thank every member of the Code Project for making it such a great place for a beginner to learn!

Heath Stewart15-Feb-05 5:52

Save and Get image data from database

15-Feb-05 5:52

The volume names are what you use to read/write from/to the volume, like C: or A:, or - if it has specified an actual volume name (like I name my root drive with Windows installed on it "System") - it is the name given to the volume. The API you found in that post - GetVolumeInformation - explains it quite well.

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Sasuko13-Feb-05 5:41

Sasuko

13-Feb-05 5:41

Can someone show me C# code to save and get an image data from/in a mdb database.
Please i can't use SQL SERVER code or VB.NET code, thanks. Smile | :)

Re: Save and Get image data from database

Heath Stewart13-Feb-05 7:16

Re: Save and Get image data from database

13-Feb-05 7:16

Please click "Search comments" before posting to search for previous replies. This question has been asked many times. See http://www.codeproject.com/script/comments/forums.asp?msg=1035557&forumid=1649&XtraIDs=1649&searchkw=database+image&sd=11%2F15%2F2004&ed=2%2F13%2F2005#xx1035557xx[^] for one recent reply.

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Sasuko13-Feb-05 11:27

Sasuko

13-Feb-05 11:27

Oh finally, tnx!

whidbey - where is Global.asax codebehind file

abcxyz8213-Feb-05 2:35

13-Feb-05 2:35

How can I have codebehind file for global.asax file and how to reference it in global.asax as I want to execute some application start up code in Application_Start so I can access global variables like Global.HostName, Global.portalName and so on.

I am using VS005 beta1 - TecheEd 2004

REgards.
MaulikCE.

Heath Stewart13-Feb-05 7:15

13-Feb-05 7:15

Whidbey (.NET 2.0) introduced partial classes, which allow a class to be defined by two different source files. VS Whidbey (VS 2005) uses this to replace code-behind files.

To see hidden files like the partial classes (also used by forms designers to separate user code from designer code), click the Project -> Show Hidden Items (or something similar - I don't remember the exact text off-hand) menu items while a file in your project is selected.

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abcxyz8214-Feb-05 3:28

14-Feb-05 3:28

I have tried with "Show all files" and "Refresh" button in the solution explorer but couldn't see the form designers' codebehind and global.asax.cs...

Here's my story:

VS 2005 doesn't offer global.asax file, when I create File>New>Website...So, I have tried adding it mannually..So, I went to Add new item...so, it shows visual studio installed templates...I selected "Global Application Class"...but what's this!!!! ( Place code in seperate file checkbox is already disabled ) So, I have to have acccept inline coding ( it gives Application_start, Session_start in global.asax file itself) but I want sepearate class i.e. codebehind file..

Any help regarding this would greatly be appreciated!!!

REgards
MaulikCE.

Heath Stewart14-Feb-05 8:27

14-Feb-05 8:27

You'll need to define a class that extends HttpApplication in your project and set the Inherts attribute to that fully-qualified class name:

<%@ Application Language="C#" Inherits="MySite.Application" %>

You can then code in a separate file, although I wonder why. Whidbey extends IntelliSense to server-side script and the class is still compiled when parsed. You can even pre-compile an entire site, now. See ASP.NET 2.0 Internals[^] for this and more information.

For a look at the differences between tradition "code-behind" and how it will work in Whidbey, see ASP.NET 2.0 Compilation Model Changes[^].

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abcxyz8214-Feb-05 21:40

14-Feb-05 21:40

Thanks Heath, I have tried to apply what I can perceieve from your comment but It constantly gives build error - "Could not load type 'MySite.Application'."...Its tiresome!!!

So, At last I have decided to put all code here rightaway(though I feel its bad), so you can throw some light where I am making mistakes in adapting Whidbey...

//Applicaiton class

<br />
using System;<br />
using System.Web;<br />
<br />
public class Application: HttpApplication<br />
{<br />
	public Application()<br />
	{<br />
		// TODO: Add constructor logic here<br />
	}<br />
<br />
    public void Application_Start(Object sender, EventArgs e)<br />
    {<br />
        // Code that runs on application startup<br />
<br />
    }<br />
 ...<br />
}

Here's the only line I have in global.asax
<%@ Application Language="C#" Inherits="MySite.Application" %>

I have even tried, <%@ Application Language="C#" Inherits="Application" %> but same error!!!

D'Oh! | :doh:

REgards.
MaulikCE..

Heath Stewart15-Feb-05 5:57

15-Feb-05 5:57

"MySite.Application" is what you're supposed to replace. If you read the documentation for the @Application element, the Inherits attribute is the namespace + class name. Whatever namespace you use for your code you must add before Application, as you've defined your class.

I still recommend you use the file itself. You still get IntelliSense and you can compile the entire site using the links I gave you. If it's a matter of protecting your code 1) a developer could easily use something like ildasm.exe or ".NET Reflector" or any other disassembler or decompiler to see your code, or 2) simply change the Inherits attribute to point to a different type if you're concerned about security (and remember that security through obscurity is no security at all).

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abcxyz8215-Feb-05 6:47

15-Feb-05 6:47

Thanks again Heath,

well "MySite" is the dummy website I have created and I dont see the namespace keyword in newly created website - "MySite"...What I have is one default page with declaration like "public partial class" enclosed by no namespace declaration thats why I have tried applying "Application" and "MySite.Application"...

Its great to hear security stuff and vulnerability of .NET from ildasm. Anyways let me cleary stat the problem.

problem:
Presently I have full fledged portal based web application running up and fine in VS2003. There I have my global.asax.cs which does some processing in global events and sets few variables of this class to name, "ConnectionString", "hostpath" and many more, so can easily be accessed in all pages by Classname.VariableName (global.ConnectionString)...And this application also does initliazation of 2-3 classes in global events..

So, I need to have 2 things in inline scripting i.e. writing all code in global.asax),

1) Setting public variables as I said for Connectionstring, so I don need to change code in all my pages which currently references them with "global.Variable" way

2) Inititalizing other classes from global events..

I think main problem is "Codebehind" attribute which is taken away in Whidbey, And I think what you are saying could be an workaround to my problem. If it works then my last question would be "Is it true that you cant have codebehind feature with global.asax which's being considered a great boon to ASP.NET against ASP?"

Look forward to hearing from you.

abcxyz8215-Feb-05 6:55

15-Feb-05 6:55

Things written below are with respect to "Whidbey"

So, I need to have 2 things in inline scripting i.e. writing all code in global.asax),

1) Setting public variables as I said for Connectionstring, so I don need to change code in all my pages which currently references them with "global.Variable" way

2) Inititalizing other classes from global events..

I think main problem is "Codebehind" attribute which is taken away in Whidbey, And I think what you are saying could be an workaround to my problem. If it works then my last question would be "Is it true that you cant have codebehind feature with global.asax which's being considered a great boon to ASP.NET against ASP?"

REgards.
MaulikCE

Heath Stewart15-Feb-05 7:28

15-Feb-05 7:28

The default namespace for a file in C# (which works differently than VB.NET in this regard) is the combination of the root project namespace you can find in the Project properties plus any folders you define. Of course, in C# you can change the namespace regardless of the location or even the project root namespace, unlike VB.NET that combines these things in the same way but in a cummulative manner, meaning that you never repeat the root or parent namespace in a source file otherwise you'll get a much longer, practically doubled namespace!

"Code-behind" wasn't removed in Whidbey, it was redefined to use partial classes instead of the previous method, which was multiple inheritence. The page (.aspx file) inheritted from the code-behind class, which inheritted from the Page class. Scary, and an unnecessary burden on the CLR.

Both goals could be solved by using another class, perhaps called Globals (seems to be common), rather than overloading the HttpApplication class unnecessarily. Since any changes to Web.config for the application (in the application root) or certain other events will tear down the AppDomain, you must make sure you re-initialize your properties correctly. Pretty much any way you do it will work.

If you don't need global.asax don't use it. This wasn't nearly used as much as originally intended (I gather) which is probably why it was removed from the default project files.

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MSpaint TextBox..

jk chan12-Feb-05 20:43

jk chan

12-Feb-05 20:43

Hi all

I am C# programmer.. For my project i want to create a textbox like in Mspaint,which restrict the entering of characters upon reaching the Size.

I tried with MeasureString.. But not works

Pls tell if anyone knows how to do it..

Warm regards
Krishnan

If u can Dream... U can do it

Re: MSpaint TextBox..

Heath Stewart13-Feb-05 7:09