using ref in C# for reference types - C# Discussion Boards

Re: Starting a GUI app with a windows service in C#

29-Jul-04 5:23

An alternative to what Chris said is to run the service as a particular user with local login rights and an associated desktop session (if they don't, a new should be initialized when the service logs in as that user), like your user account. In this case, however, the service will only run in the specified user's desktop session (which could be in the background of another current desktop session for an interactive user).

In most cases, what Chris said is best but I just wanted to present this alternative.

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satorical29-Jul-04 6:13

satorical

29-Jul-04 6:13

Thanks very much to both you and Chris. Chris' solution would work except that I need to have the service access a network share folder. The Local System account can't access the network resource. I tried using my own account to run the service, but my service started the test application in the background - I could see the process, but no desktop interaction. What you say makes it sound like the test application should be interacting with my desktop session, since the service is running under my account and I'm currently logged in. Can you think of any reason why it isn't?

Re: Starting a GUI app with a windows service in C#

Heath Stewart29-Jul-04 6:23

how to get cd information

29-Jul-04 6:23

You could use impersonation. See the documentation for the WindowsIdentity.Impersonate method in the .NET Framework SDK for an example.

This won't prompt for credentials, however. That's your code's job but simply requires a dialog with a couple TextBoxes and Buttons (or however you want it to look).

Another option - though a hack - is to set the password for the local SYSTEM account on both machines to the same password. This has worked for several other people in workgroup setups before.

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civc28-Jul-04 13:23

civc

28-Jul-04 13:23

hi there,

i would like to receive information about a cd/dvd in my cd-rom drive. i already use the freedb and volumeinfo article's code to receive the audio track names and other details (thx a lot for the code!).

what i need is the following:
- i want to get the disk size in bytes. this works with a system.management.managementobject, but _not_ for audio cd's, it returns 0 (it works for mixed cd's and dvd's e.g.).
- what i need even more is the date when the cd/dvd was pressed/burned. this must work somehow! nero shows it! also windows shows a date for each track...

could anyone help me with that please?

greetings, have a nice week,
civc

How to enumerate windows belong to an instance?

Old Gun28-Jul-04 13:04

Old Gun

28-Jul-04 13:04

Please help me

Re: How to enumerate windows belong to an instance?

Dave Kreskowiak28-Jul-04 14:17

Dave Kreskowiak

28-Jul-04 14:17

You have to be alot more specific about what your asking and what your doing. Instance of what?

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

using ref in C# for reference types

vista2728-Jul-04 12:48

vista27

28-Jul-04 12:48

please correct me if anything i state is incorrect about ref in C#. i'm trying to make sure i understand these 100%.

- using a ref parameter in C# for VALUE types (eg ref Int32 i) is basically the same thing as using "int* pInt" in C++.

- for reference types, C# defaults to passing references, so any function in C# (Without ref or out keyword) when passing references is basically also "classType* pObj" in C++.

- when using the REF keyword with a REFERENCE type in C#, this is essentially the same as pointers to pointers in C++. that is, in C# a function "void func (ref ClassType p)" would be written equivalently in C++ as "void func (ClassType** p), and when p is used in the C# function, such as p.memberFunction(), the equivalent in the C++ function would be (*p)->memberFunction(). in other words, in C# the levels of dereferencing are hidden from the programmer, wheras in C++ you must dereference the proper levels yourself.

is my understanding of how C# implements references correct? thanks.

Heath Stewart28-Jul-04 13:00

28-Jul-04 13:00

Yes, but with one other thing. If you reassign a parameter reference without ref or out, the variable that was passed to the method will not reference the new object.

With this comes something very important, one of the few things that can truly crash the CLR. If you are P/Invoking a function that takes an LPTSTR or something as an [out] variable, do not use out or ref in your managed declaration (unless the function parameter type is LPTSTR*). To make sure the marshaler knows to reassign the parameter, use the OutAttribute instead.

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vista2728-Jul-04 13:58

vista27

28-Jul-04 13:58

you mean like so:

void function (MyClass myObj)
{
myobj = new MyClass();
}

so in this case, it appears that after the function call the reference to the new MyClass obj is lost and is just garbage collected, and the ref passed in would remain referring to whatever it was before the function call. right?

Heath Stewart29-Jul-04 4:17

29-Jul-04 4:17

Yes, that is correct. Consider the following example:

using System;

class Test
{
  static void Main()
  {
    Exception e = new Exception("From Main()");
    Console.WriteLine(e.Message);

    A(e);
    Console.WriteLine(e.Message);

    B(ref e);
    Console.WriteLine(e.Message);
  }

  static void A(Exception e)
  {
    e = new Exception("From A()");
  }

  static void B(ref Exception e)
  {
    e = new Exception("From B()");
  }
}

The output would be:

From Main()
From Main()
From B()

Exception was just the first object that came to mind, but any reference type - and in this case, value types - would do.

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MKlucher28-Jul-04 18:12

MKlucher

28-Jul-04 18:12

This is a side question, but so similar I didn't want to start a whole new thread for it. I have a Managed DLL that takes a int* but I can't seem to pass anything that works (ref, out) it's a Managed DLL so I'm not using Pinvoke, but I am wondering if there is a way to do this without using unsafe code or changing the Managed DLL code (Although that probably what I'll have to do).

Thanks!!

Heath Stewart29-Jul-04 4:28

IDispDataVwDataConn => casting Server Explorer node to this interface

29-Jul-04 4:28

An int* in unmanaged code (even though your targeting the CLR with your C++ compiler) is still a pointer to a native int, not a managed int. Try using System::Int32*. If that doesn't work, I recommend you ask in the Managed C++ forum. I've used MC++ in the past but not a whole lot. Sorry.

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mikker_12328-Jul-04 12:18

Re: IDispDataVwDataConn => casting Server Explorer node to this interface

28-Jul-04 12:18

I'm developing add-in for VS and am having extreme trouble with getting ConnectionString from node in Server Explorer. I've done most of the job getting one of the node as UIHierarchyItem but I can't cast either it or it's .Object to IDispDataVwDataConn which is type when I select node and then look into property window (I found that interface in VS7DataProject)...

Maybe the problem is that the object I am casting is a COM object, the object I am casting to is a .Net wrapper - they are not really the same thing, though I was hoping all the gory details would have been taken care off for me (interop being so seemless). If anyone has a suggestion as to how to get said COM object to cast to the .Net interop type or some other way of accessing the COM object's properties directly...then that would possibly solve the whole problem....

Tnx in advance to anyone who tries to help...

Heath Stewart28-Jul-04 12:41

Re: IDispDataVwDataConn => casting Server Explorer node to this interface

28-Jul-04 12:41

The IDispDataVwDataConn interface must be declared in your managed code (resumably C# since you're in this forum) with the ComImportAttribute (so that the CLR QI's for the interface instead of doing a type cast), the correct GuidAttribute (with the right IID), and the InterfaceTypeAttribute with the correct value that dictates from which interface(s) the interface in question derives. The methods must also be in the correct order (when derived from IUnknown or a dual interface) and have the correct DispIdAttribute values (when derived from IDispatch or a dual interface).

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mikker_12329-Jul-04 5:14

Re: IDispDataVwDataConn => casting Server Explorer node to this interface

29-Jul-04 5:14

First of all tnx...

Second - am still at newbee level I guess as I can't get this thing working... So if you can I would be grateful if you could provide more pointers or answers to my questions. I included code I tried to made.

Question:
---------
Is IDispDataVwDataConn really the one needed to be set with all those attributes and defined in mine project? As it is already defined in VS7DataProject and it's managed code.
UIHierarchyItem.Object is COM object...

Code:
-----

<br />
//////////////////////<br />
public class TempClass<br />
{ <br />
// Already implemented logic for getting instance of EnvDTE... so it is inrelevant<br />
EnvDTE containerApplication; <br />
// ComboBox I'm filling... already defined <br />
ComboBox cmbConnection; <br />
<br />
void LetsPresumeThisFunctionGetsCalledWhenItsNeeded()<br />
{<br />
EnvDTE.Window win = containerApplication.Windows.Item(Constants.vsWindowKindServerExplorer);<br />
UIHierarchyItem uih = ((UIHierarchy)win.Object).GetItem("Data Connections");<br />
<br />
if (uih.Collection.Count > 0)<br />
{<br />
cmbConnections.Enabled = true;<br />
<br />
foreach(UIHierarchyItem item in uih.UIHierarchyItems)<br />
{<br />
// So what I would try to do here would be:<br />
// IDispDataVwDataConn dc = (IDispDataVwDataConn)item.Object;<br />
// cmbConnections.Items.Add(dc.ConnectionString); <br />
} <br />
} <br />
} <br />
}<br />
//////////////////////<br />

tnx again mate...

Heath Stewart29-Jul-04 6:03

Re: IDispDataVwDataConn => casting Server Explorer node to this interface

29-Jul-04 6:03

I wasn't able to find the assembly that defines the IDispDataVwDataConn interface you mentioned to make sure it is attributed correctly, but there is the Microsoft.VSDesigner.dll assembly (in the Common7\IDE sub-directory of your VS.NET installation directory) that has the IDataConnectionsService which could accomplish the same thing.

Perhaps if you told me what the full assembly name is and where I might find it (I've looked to no avail) I might be able to help you better.

Make sure you also have referenced that assembly in your project, otherwise the interface won't be found when compiling (but I'm assuming you've done that and are having runtime problems).

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mikker_12329-Jul-04 6:34

Re: IDispDataVwDataConn => casting Server Explorer node to this interface

29-Jul-04 6:34

Add Reference => COM => Visual Studio.NET Data Projects (DLL can be found at <path to="" vs.net2003="" dir="">\Common7\Tools\VDT\vdt70p.dll).

I also saw that interface (IDataConnectionsService) but I guess it can do no good as first one is used. If you wish to see what I mean start VS.NET => Server Explorer => expand Data Connections node => right click on any exiting one => Properties => Next to name of is type and it's IDispDataVwDataConn.

Cheers mate...

Heath Stewart29-Jul-04 8:58

Re: IDispDataVwDataConn => casting Server Explorer node to this interface

29-Jul-04 8:58

Since it's being imported from a typelib, it is a COM wrapper (RCW) and is an imported interface (just to be sure it was correct, I double-checked). Casting the Object property should work (and obviously doesn't). Have you tried just casting the node itself?

If anything, there is a developer forum for the VSIP (developing and integrating components with VS.NET itself) on the MSDN[^] web site somewhere. You might consider that approach.

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mikker_12329-Jul-04 9:20

29-Jul-04 9:20

As said in first post I tried casting both Object and node... unsuccesfuly. Also I found extensibility newsgroup (microsoft.public.vstudio.extensibility) with same subject but no answer (guys came as close as I did). Google search => also founde one unfinished discussion. So I guess I should just quit it...? Smile | :)

read-only

Anonymous28-Jul-04 12:17

Anonymous

28-Jul-04 12:17

how do I check if a file with a given path is read only?

mikker_12328-Jul-04 12:22

28-Jul-04 12:22

Use =>

System.IO.File.GetAttributes(string pathToFile);

and then compare it using System.IO.FileAttributes enum...

Anonymous28-Jul-04 12:40

Anonymous

28-Jul-04 12:40

But the following lines never give anything but '1'. How am I to distinguish between read-only and read/write files?

System.IO.FileAttributes att = System.IO.File.GetAttributes( this.currentFolder);
MessageBox.Show(att.CompareTo(System.IO.FileAttributes.ReadOnly)+"");

Heath Stewart28-Jul-04 12:43

28-Jul-04 12:43

Bitwise conditions:

FileAttributes attribs = File.GetAttributes("file.txt");
if ((attribs & FileAttributes.ReadOnly) != 0) Console.WriteLine("Read-only");
else Console.WriteLine("Read-write");

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