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This is the documented and expected behavior. All COM methods (and, by extension, properties) are supposed to return HRESULTs (as yours does), and what COM clients like VB and .NET via COM interop see is return values (although in .NET you can attribute your methods with PreserveSigAttribute - among other ways - to make sure an HRESULT is returned as an Int32 since the return result code might be important and may not be an error (like S_FALSE).
I recomend that you read Creating a CCW for COM enabled non .NET applications[^] here on CodeProject, as well as Exposing .NET Framework Components to COM[^]. Make sure that you hard-code GUIDs with the GuidAttribute and never change published interfaces (i.e., interfaces you've released unto the world). Always derive new ones. Also never use auto-generated class interfaces. Define your interfaces explicitly and implement your class interface as the first interface in your implementation list.
Also, what examples are you looking at? I've read about every article and API doc in MSDN and COM methods are all return HRESULTs or SCODEs (legacy) - it's part of the COM spec to do so. VB (pre-.NET) interprets [retval]s as return values, just like tlbimp.exe and VS.NET do when importing a typelib. Other late-bound clients like Windows Script (VBScript, JScript) do so as well.
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles]
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You're actually supposed to use the PreserveSigAttribute when you do this. Some times the samples are incorrect. Try compiling the following:
using System;
using System.Runtime.InteropServices;
[assembly: ComVisible(true)]
[assembly: Guid("519a4822-f224-47fa-bdc7-8037829365dc")]
[InterfaceType(ComInterfaceType.InterfaceIsDual)]
[Guid("f9b77b61-b4f0-4be4-9c53-ded9592e90c6")]
public interface ITest
{
[DispId(0)]
int Foo(string value);
}
[ClassInterface(ClassInterfaceType.None)]
[Guid("ae5e53c8-54d6-4667-9396-582f5c8611bf")]
public class Test
{
public int Foo(string value)
{
return value.Length;
}
}Compile using:
csc.exe /t:library test.cs Next, register the library and generate a typelib:
regasm.exe /tlb test.dll Finally, view the typelib:
oleview.exe test.tlb You'll see the following:
[
uuid(519A4822-F224-47FA-BDC7-8037829365DC),
version(1.0),
custom(90883F05-3D28-11D2-8F17-00A0C9A6186D, Test, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null)
]
library Test
{
importlib("mscorlib.tlb");
importlib("stdole2.tlb");
interface ITest;
[
odl,
uuid(F9B77B61-B4F0-4BE4-9C53-DED9592E90C6),
version(1.0),
dual,
oleautomation,
custom(0F21F359-AB84-41E8-9A78-36D110E6D2F9, ITest)
]
interface ITest : IDispatch {
[id(00000000), propget,
custom(54FC8F55-38DE-4703-9C4E-250351302B1C, 1)]
HRESULT Foo(
[in] BSTR value,
[out, retval] long* pRetVal);
};
[
uuid(AE5E53C8-54D6-4667-9396-582F5C8611BF),
version(1.0),
custom(0F21F359-AB84-41E8-9A78-36D110E6D2F9, Test)
]
coclass Test {
[default] interface _Object;
};
};If you used PreserveSigAttribute, then it would simply be HRESULT Foo(BSTR value).
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles]
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Also, while we're on the subject.
How do strings returned from .net work?
If I have a method string getSomething()
I have to call it as: HRESULT getSomething(BSTR* result);
It seems I have to allocate the string for the result.
I'm doing:
CComBSTR result(20);
and call it:
getSomething(&result.m_str);
what happens if I return string longer than 20 characters? Does CLR allocate more chars?
I tried looking in MSDN, but I couldn't find any information. It seems all examples I can find only deal with ints or doubles.
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It's an [out, retval]. Most often, you don't allocate these as the caller. Merely declare a variable and pass the address of the variable. Also, if you read the documentation for the CComBSTR class, you'll see the following remarks:Memory Leak Issues
Passing the address of an initialized CComBSTR to a function as an [out] parameter causes a memory leak.
In the example below, the string allocated to hold the string "Initialized" is leaked when the function OutString replaces the string.
CComBSTR bstrLeak(L"Initialized");
HRESULT hr = OutString(&bstrLeak);
To avoid the leak, call the Empty method on existing CComBSTR objects before passing the address as an [out] parameter.
Note that the same code would not cause a leak if the function's parameter was [in, out].
So, as you see - don't initialize it. You also don't need to mess with m_str. Since the CComBSTR contains only one member - m_str - passing the address of the CComBSTR instance is passing the address of the m_str (because of the way the class/struct is aligned).
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles]
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I see. thanks.
Do you know if there are any restrictions on types you can use within .net COM client?
I have my C# class do:
new SqlConnection(connectionstring)
and it throws access violation exception:
Error Msg: System.TypeInitializationException: The type initializer for 'System.
Data.SqlClient.SqlConnectionFactory' threw an exception. ---> System.TypeInitial
izationException: The type initializer for 'System.Data.SqlClient.SqlPerformance
Counters' threw an exception. ---> System.AccessViolationException: Attempted to
read or write protected memory. This is often an indication that other memory h
as been corrupted.
at System.Data.ProviderBase.DbConnectionPoolCounters.GetInstanceName()
at System.Data.ProviderBase.DbConnectionPoolCounters.InitCounters(String cate
goryName, String categoryHelp)
at System.Data.SqlClient.SqlPerformanceCounters..ctor()
at System.Data.SqlClient.SqlPerformanceCounters..cctor()
--- End of inner exception stack trace ---
at System.Data.SqlClient.SqlConnectionFactory..ctor()
at System.Data.SqlClient.SqlConnectionFactory..cctor()
--- End of inner exception stack trace ---
at System.Data.SqlClient.SqlConnection..ctor()
at System.Data.SqlClient.SqlConnection..ctor(String connectionString)
When I use my client thru C#, it's all fine. My C++ COM clinet is very simple for the test case, it just creates COM object and calls one method with no parameters and no return values (I did that to see if it was some memory problem in C++ client).
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I have a form with a fairly large client area. Therefore I allow it to scroll. On the form I have OK/Cancel Buttons. I really would like them to remain stationary. I tried a Forms Toolbar, but it scrolls with the client area.
Any ideas?
Thanks!
Mark
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You could put a panel inside the form that would be your effective client area. The panel would be set to allow scrolling, but not the form. The panel would leave enough room for the OK\Cancel buttons, which would be on the form, not the panel.
Brian
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Thanks Brian! I should have thought of that.
Mark
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reference: http://msdn.microsoft.com/library/en-us/gdi/monitor_4mr7.asp?frame=true
========================================================================
SETUP:
I have two monitors using a dual video output NVIDIA Quadro NVS. One of them is the primary. The other is NOT part of the VIRTUAL DESKTOP.
APPLICATION:
One monitor will be for the cashier running her program and the other Independent Monitor will be for WEB, FLASH and VIDEO CONTENT to be played on, plus a section of the monitor for the running itemize total. I don't want the cashier to be able to move the mouse or window accidently over to the other monitor.
QUESTION:
How do I accomplish this? The Microsoft hyerlink above is quite cryptic for a C# guy learning C++. If anyone has another solution or a way to impliment this idea or can tell me some books to read, I would highly grateful, since I am on a very TIGHT SCHEDULE. THANK YOU ADVANCE.
Peter B.
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Dunno if this helps, but this is how I place a form over the second monitor:
Screen [] screens = Screen.AllScreens;<br />
<br />
if (screens.GetUpperBound(0) > 0)<br />
{<br />
Screen secondary = screens[1];<br />
secondMonitor.Bounds = secondary.Bounds;<br />
secondMonitor.MinimumSize = secondary.Bounds.Size;<br />
}<br />
else<br />
{<br />
secondMonitor.Visible = false;<br />
}
My second monitor is part of the virtual desktop tho. Why isn't yours ?
Christian
I have drunk the cool-aid and found it wan and bitter. - Chris Maunder
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Hi,
I want to send to SQL server a query I want to get randomly generated 100 rows where they are no generated before. I made my query like below:
mySqlCommand.CommandText = "SELECT name,rand(name) FROM people LIMIT 100 WHERE generated_before IS NULL";
Gives system error???
Thank you,
Cem Louis
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You want to generate 100 rows, or get back 100 rows at random ?
Christian
I have drunk the cool-aid and found it wan and bitter. - Chris Maunder
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I'm not sure when you get the LIMIT keyword from, it doesn't appear to be a valid T-SQL keyword.
Try
SELECT TOP 100 ....
Also, the RAND() function only accepts interger types. I am assuming that name is a string of some kind. I am not sure what you are trying to do with RAND()
If you can explain more about what you are trying to do I might be able to help more.
Do you want to know more?
Not getting the response you want from a question asked in an online forum: How to Ask Questions the Smart Way!
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Anyway I did it like below:
"SELECT TOP 100 name FROM people ORDER BY NEWID()"
Cem
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I have a project with several Forms open at the same time. Is there a way I can keep certain ones always on top? At runtime, each time the user clicks a form it gets focus and hides an overlapping forms.
Thanks!
Mark
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Set the TopMost property of the form to true.
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Waaaaaaaaaaahhhh
Have the same problem, to lazy to research and test code.
Please help the weaklings and the lazy ones...
Thank you very much for your help
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hi all,
i would like to write C# code that would allow a user to upload images to a file on a remote server any ideas or solutions for me pleez. this would require ftp access and i am uncertain how i am going to integrate this into the app. the idea is the to upload new images when the need arises...
many thanks
butchzn
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Uploading files greatly depends on what the server protocol is. If you're using HTTP, for example, the HttpWebRequest already supports this. Since you're requiring FTP, realize that the current .NET BCL has no FTP support - but don't let that stop you.
Some articles on this site and others have simply wrapped the ftp.exe application in a class library. This is dodgy and not very well designed. A proper design - like HttpWebRequest and HttpWebResponse - would extend WebRequest and WebResponse, classes for pluggable protocols.
It just so happens that there's a good example in the Microsoft Knowledge Base: http://support.microsoft.com/default.aspx?scid=kb%3BEN-US%3B812409[^]. It has a link at the bottom to GotDotNet (a Microsoft developer community site) with the full source.
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles]
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Is there a simple way to paint in a colour inverse to the current image?
(I'm implementing a mouse-drag selection box, and want to just draw a rectangle on screen where each pixel is the inverse of whatever's already there)
--
Help me! I'm turning into a grapefruit!
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The inverse colors are easy to calculate. Subtract the red, green, or blue (RGB) component from 255:
Color Invert(Color c)
{
int r = 255 - c.R;
int g = 255 - c.G;
int b = 255 - c.B;
return Color.FromArgb((int)c.A, r, g, b);
}But there's a easier way, and it's a little faster since the Color structure stores the ARGB (alpha, red, green, blue) as a single 64-bit number (though most members reflect a 32-bit number):
Color Invert(Color c)
{
Color c2 = Color.FromArgb(0xffffff - c.ToArgb());
return Color.FromArgb((int)c.A, c2);
}All this is assuming you keep the same alpha value, which is typically want you want to do.
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles]
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Microsoft, I noticed, doesn't use a lot of unsigned types, even when private or internal (since unsigned types are not CLS-compliant, but for private and internal members I don't see why it matters). If they used a signed int, solid black would be -1, something that may pose a problem for those using reflection. Maybe Microsoft plans on supporting CMYK along with an alpha channel in the future (requiring more than 32 bits).
It's all just speculation, though. I really don't know.
This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft
[My Articles]
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Thanks, I was figuring I was going to have to do something like that - but was hoping I'd just be able to set my pen colour to some magic constant that'd tell the gdi functions to draw in an inversed colour
--
Help me! I'm turning into a grapefruit!
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can you explain the method in that madness? Support for 36,48,64 bit colors in the future?