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First, change the class to a struct. This allocates the data on the stack so it will not be moved. While this isn't the direct cause of your problem, it may lead to them. If it's a class - which is allocated on the heap - the GC (Garbage Collector) may move it when necessary and your handle that your enumerator is using would be invalid. Declaring this as a struct should also fix the other error.
There is a problem with your EnumChildWindows as well. An HWND is a processor-dependent type. You should really declare this as IntPtr, which works well since P/Invoking other unmanaged Windows APIs will use IntPtr and Control.Handle (the HWND for the control) is also of type IntPtr. Any native int or unsigned int should be declared as an IntPtr.
Also, for your struct, just use LayoutKind.Sequential. You really don't even need that, however, since the memory address to your struct's instance is being passed to your enumerator so it doesn't need to be marshaled for use with unmanaged code. Just a couple of tips.
Microsoft MVP, Visual C#
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Thanks... Heath Stewart
The tips helped ..
But i cannot change class to struct. Since struct won't allow the same struct as a member
Shaju Mathew
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In that case, use a GCHandle to pin the class instance in memory. The GC (Garbage Collector) may relocate the object in memory, so the address would change. Unmanaged code can't deal with those changes so you'll get all sorts of errors since your object isn't where it's supposed to be.
You can find more information about the GCHandle class in the .NET Framework SDK.
Microsoft MVP, Visual C#
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When I was marshalling EnumChildWindows, I declared the function like that:
[DllImport("user32.dll",SetLastError=true)]<br />
public static extern bool EnumChildWindows( <br />
IntPtr hWndParent,<br />
User32Functions.EnumWindowsCallback lpEnumFunc,<br />
IntPtr lParam<br />
);
The point is, why do you need to pass a class or struct as the third parameter?
I followed the MSDN recommendation and called the function like that:
GCHandle gch=GCHandle.Alloc(this.twHandles);<br />
User32.EnumChildWindows(handleParent,this.enumThreadCallback,(IntPtr)gch);<br />
gch.Free();
Here this.twHandles is a text writer, which i later (in the callback function) use like so:
private bool CaptureEnumThreadWindows(int handle, IntPtr param)<br />
{<br />
GCHandle gch=(GCHandle)param;<br />
TextWriter tw=(TextWriter)gch.Target;<br />
twHandles.Write(handle.ToString()+" ");<br />
twHandles.Flush();<br />
return true;<br />
}
Anyway, MSDN recommends to use GCHandle , 'so the delegate does not get moved by GC before the call ends, however I was trying to use without GCHandle, just passing IntPtr.Zero as the last parameter and it works anyway. Frankly I don't understand how this (GCHandle) can prevent the delegate from being moved by GC, but that's what MSDN says. (see GCHandle sample)
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Thanks Ael
GCHandle worked well And it solved my problem.
Shaju Mathew
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Hy.
My problem is that I'm new in this field (DirectShow filter) and I need to use a particular filter in my app.
I think is possible but I really don't know how.
So , I have a DirectShow filter with the AX extension (executable , I think)
written in C++ and I want to use it in my C# app.
Can anyone help me ?
Thanks.
Angel
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If you're working with DirectX in C#, I recommend you take a look at the Managed DirectX 9.0 extensions - written from ground-up for .NET - at http://msdn.microsoft.com/directx[^]. You can also download the Summer 2003 Update (the full thing - just the latest SDK and runtime) from there.
Unfortunately, Managed DirectX does not contain a managed assembly or classes for DirectShow (at least not yet; I'm really not sure of future plans). If it was, you'd be able to register your filter's COM server and use the CLSID like you can with other managed classes in Managed DirectX 9.0.
There are several ways you can use your filter, though. One would be to write a native C/C++ library (DLL) that instantiates your filter's COM object and streams data through it. You could export certain functions that do this and use P/Invoke in C# to execute those exported functions (see the DllImportAttribute class documentation in the .NET Framework SDK).
Another way would be to write a mixed-mode Managed C++ assembly that can use native functions and wrap them in a managed class. You can then use this assembly in your C# project. Thanks to the Common Language Infruastructure (the CLI), languages can interoperate with each other because they compile to a Common Intermediate Language, or CIL.
Microsoft MVP, Visual C#
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Thanks for answering.
What you are saying surely is interesting but I'm kind of on a time schedule with this app.
I found NetMaster's DShowNET on this site and is working just fine in C#.
My problem is that the video I receive comes from a network , so the first filter in my graph should be one that can extract data from a net. I think I have the filter but when I try to use DShowNET's EnumFilters NEXT function I receive an error about the IBaseFilter variable.The code compiles ok , the error comes at runtime.
****************
IBaseFilter[] pf;
IEnumFilters pe=null;
int fetch;
int hx,cod;
hx=gr.EnumFilters(out pe); // hx=0 after this
cod=pe.Next(1,out pf, out fetch); // Error : "Can not use SizeParamIndex for byref array parameters.
// gr is the graph.I've tested it and it works
*****************
Normaly , it shoud be possible to get graph filter's info , add and replace filters in C# using DShowNET.dll , but I can't get pass this error.
Any ideeas ?
Thanks in advance.
Angel
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I'm not familiar with that project. If yo uhave questions specific to that project, you should redirect them to the message board at the bottom of that article.
Microsoft MVP, Visual C#
My Articles
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Try replacing the current IEnumFilters Next COM signature with:
int Next([In] int cFilters, out IBaseFilter pFilter, [Out] out int filtersFetched);
Example client code would be:
FilterInfo fi = new FilterInfo();
while(0 == enumFilters.Next(filtersToFetch, out filter, out filtersFetched))
{
filter.QueryFilterInfo(fi);
}
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Hello,
I am new to this forum but I am most definitely not new to programming. I have been coding in C++ console for allmost 3 years and C++ console structures, pointers, trees, etc. for over a year. After completing a college course in VB.net I have found that C# is the ultimate in GUI programming. Integrating my console C++ programs into C# has been a breeze! I would say if you know C++ console very well and VB.net and with a couple of C# books you can become expert in no time. I have been developing a program in C++ console for the past year and I have only recently migrated to C# last month in April. C# has probably cut an least year off of my development time. I fully expect a release date on or around Sept.8,2004. If anyone reading this thread would like to follow my C# progress please check the following link...
http://www.demasoni.com
I would recommend C# for GUI C++ programming.
jjsjr
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Thanks very much for the advertisement...
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NO problem David, I rarely talk about the quality of a product but C# is a very nice development enviroment and my current software project is proof of it.
BTW: This site has some of the best examples on the web for C#. It has helped me with my current project. I will use it again from time to time.
js
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how to config a serial number in InstallShield.
Thank in advance.
QuocBao
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The InstallShield documentation explains this and gives examples if you look. This has nothing to do with C#.
Microsoft MVP, Visual C#
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I'm writing an MP3 player, with queueing capabilities - it writes the queue to a temporary text file, and I also have another form in the app that allows me to view the queue. This works fine, but I can't refresh the queue automatically. I would like to be able to just call the writeQ function in the main form to write the queue, then call the queue viewer forms' load function which would read the necessary data. But, my problem is, I don't understand how I can get the handle of the main form to call the writeQ. simply doing a MainPlayer mainP = new MainPlayer() then calling mainP.writeQ() (MainPlayer is the main form class) won't work, because it'll try to read the listBox in the queue viewer form...Anyone know how I could force it to read the listBox in its own form? I would think I can do it using IntPtr and window handles, but I have no idea quite how to do this.
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The thing you want to do, i think is done more easily in that way.
Once the user want to change your playlist immediately you go and update the file you are writing. The other form will use a filesystemwatcher component so that once it sees that the file you want changed he will go and update the view of the playlist. If you want to do the thing you are saying you will have to mark the writeQ method as public and when you create the viewer form pass a variable of type MainPlayer with the mainform in it in the constructor and store this variable as a member and call the function writeQ in it.
From Greece:
Dimitris Iliopoulos
dimilio@yahoo.com
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I have a TabControl with 7 different tabs. One of the Tabs has numerous text boxes and labels and a few buttons. When I run the app on this particular laptop that is running windows 2000 professional the text boxes, labels and buttons are shifted down and to the right. Part of the text boxes and labels are obscured and cannot be moved. This problem does not occur on XP nor does it happen on a Windows 2000 professional Desktop. I had to laugh when I saw it because I don't have a clue as to why it is happening. If my explaination is not clear let me know and I'll try harder to make it clear.
Any insight would be awesome!
Parrish
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Format and reinstall windows 2000 on the laptop !!! Most users play with the settings of the windows and they end up with a windows operating system missfunctioning
From Greece:
Dimitris Iliopoulos
dimilio@yahoo.com
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 What kind of advice is that? If you can't give a reasonable answer, please don't answer at all.
Microsoft MVP, Visual C#
My Articles
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Ignore that last reply. That's not a solution but in the most extreme circumstances.
On laptops - and even some desktops - it's common that the DPI (dots per inch) is set higher. Desktops are typically at 96 DPI while newer laptops (with much better displays capable of higher resolutions) are at 120 DPI. Unfortunately, the .NET Framework uses pixels, a logical unit. VB6, for example, uses twips which are a physical unit (like an inch or a point). See http://visualbasic.about.com/cs/visualbasicfaq/a/dykpixeltwip.htm[^] for more information.
How do you convert this? By P/Invoking GetDeviceCaps and initializing a couple of static properties with the scale factor. You should also handle the Microsoft.Win32.SystemEvents.DisplaySettingChanged event so that you can update these when the display settings change. See How to Write High-DPI Applications[^] in the MSDN Library.
Using those concepts, you could create a class like so:
public sealed class Display
{
static Display()
{
SystemEvents.DisplaySettingsChanged += new EventHandler(Update);
}
private Display() {}
[DllImport("gdi32.dll")]
private static extern IntPtr GetDeviceCaps(IntPtr hdc, IntPtr index);
[DllImport("user32.dll")]
private static extern IntPtr GetDC(IntPtr hwnd);
[DllImport("user32.dll")]
private static extern IntPtr ReleaseDC(IntPtr hwnd, IntPtr hdc);
private static void Update()
{
Setup(true);
}
private static void Setup(bool force)
{
if (initialized && !force) return;
logsPerPixelX = logsPerPixelY = 0;
IntPtr hdc = GetHDC(IntPtr.Zero);
try
{
if (!hdc.Equals(IntPtr.Zero))
{
IntPtr value;
value = GetDeviceCaps(hdc, 88);
logsPerPixelX = 1440 / value.ToInt32();
value = GetDeviceCaps(hdc, 90);
logsPerPixelY = 1440 / value.ToInt32();
ReleaseDC(IntPtr.Zero, hdc);
}
}
catch {}
if (logsPerPixelX == 0) logsPerPixelX = 15;
if (logsPerPixelY == 0) logsPerPixelY = 15;
initialized = true;
}
private static bool initialized;
private static int twipsPerPixelX;
private static int twipsPerPixelY;
public static int TwipsPerPixelX
{
get
{
Setup(false);
return TwipsPerPixelX;
}
}
public static int TwipsPerPixelY
{
get
{
Setup(false);
return TwipsPerPixelY;
}
}
public static int FromPixelsX(int x, ScaleMode mode)
{
switch (mode)
{
case ScaleMode.Points:
return PixelsToTwipsX(x) / 20;
case ScaleMode.Inches:
return PixelsToTwipsX(x) / 1440;
default:
throw new ArgumentException("Invalid scale mode.", "mode");
}
}
public static int FromPixelsY(int y, ScaleMode mode)
{
switch (mode)
{
case ScaleMode.Points:
return PixelsToTwipsY(y) / 20;
case ScaleMode.Inches:
return PixelsToTwipsY(y) / 1440;
default:
throw new ArgumentException("Invalid scale mode.", "mode");
}
}
public static int ToPixelsX(int x, ScaleMode mode)
{
switch (mode)
{
case ScaleMode.Points:
return TwipsToPixelsX(x * 20);
case ScaleMode.Inches:
return TwipsToPixelsX(x * 1440);
default:
throw new ArgumentException("Invalid scale mode.", "mode");
}
}
public static int ToPixelsY(int y, ScaleMode mode)
{
switch (mode)
{
case ScaleMode.Points:
return TwipsToPixelsY(y * 20);
case ScaleMode.Inches:
return TwipsToPixelsY(y * 1440);
default:
throw new ArgumentException("Invalid scale mode.", "mode");
}
}
public static int PixelsToTwipsX(int x)
{
Setup(false);
return x * twipsPerPixelX;
}
public static int PixelsToTwipsY(int y)
{
Setup(false);
return y * twipsPerPixelY;
}
public static int TwipsToPixelsX(int x)
{
Setup(false);
return x / twipsPerPixelX;
}
public static int TwipsToPixelsY(int y)
{
Setup(false);
return y / twipsPerPixelY;
}
}
public enum ScaleMode
{
Points,
Inches
}This is similar to code I developed for our application, based on the Type Microsoft.VisualBasic.Compatibility.VB6.Support, Microsoft.VisualBasic.Compatibility. You can use this to convert pixels to physical units more suitable for different display resolutions.
Microsoft MVP, Visual C#
My Articles
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I am really sorry if my answer was not reasonable. I have seen your code and it is really excellent! But lot of times and i mean (lot of times) i have installed a product of mine which worked perfectly in all of the previous installations on a computer and simply on that computer didn't play, after lot of time on debuging my code for the problem i have seen, i found that the user has deleted some keys from the registry himself  and this was the problem!!!!!! My answer was not a programming one and i am sorry, but it is true that sometimes you need to go that way!!!
From Greece:
Dimitris Iliopoulos
dimilio@yahoo.com
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Then why don't you reinstall your product? Your installation should be responsible for setting default registry keys as well as removing them during uninstall. Formatting and reinstalling the OS is a last-ditch effort. It's your application that was screwed up more than likely - thorugh no fault of your own, just the users - so it's your application that should be repaired first. There are many other things one could do before resorting to reinstalling the OS.
Microsoft MVP, Visual C#
My Articles
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Heath,
I appreciate your insight and expertise but your talking to someone who only has a very basic understanding of this type of development environment. Please forgive my ignorance. To be honest I'm not completely sure I understand how to use it. Whenever the screen size is changed do I run all my Text boxes and labels through the scaling functions to reposition them? I did incorporated this class into my code. I instantiate a Display object when I bring up my application and the Update service is called when I change the screen dimensions. I did have to make a few changes to get it to work (as I'm sure you expected). I had to add the following at the appropriate places...are they ok?
static int logsPerPixelX,logsPerPixelY;
IntPtr eightyEight = new IntPtr(88);
IntPtr ninety = new IntPtr(90);
value = GetDeviceCaps(hdc, eightyEight); // LOGPIXELSX
logsPerPixelX = 1440 / value.ToInt32();
value = GetDeviceCaps(hdc, ninety); // LOGPIXELSY
logsPerPixelY = 1440 / value.ToInt32();
ReleaseDC(IntPtr.Zero, hdc);
Because I'm not real sure how to use it, I don't understand why the logsPerPixelX and logsPerPixelY are setup but never used and why twipsPerPixelX and twipsPerPixelY are never setup?
I also don't understand why it is only one tab page out of 7 that has this problem? I have numerous other Forms that display properly. If you could just grit your teeth and drop kick me into the right areas I would be most appreciative.
If it jams, force it!!
Parrish Pope
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You don't instantiate the Display class as I presented it - it defines static methods and properties: there is no need to instantiate it (which is why I made it sealed and the default constructor private).
Yes, when your display changes you would need to run the sizes and locations of the controls through these methods. If you don't understand them, read the other links I gave you.
There is more information about programming for different resolutions at http://msdn.microsoft.com[^].
Microsoft MVP, Visual C#
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