Re: Threading using the ref statement? Wha Happen? - C# Discussion Boards

Threading using the ref statement? Wha Happen?

27-Oct-03 6:29

Sounds like you didn't instantiate the control. It looks like you got a NullReferenceException? Just 'new it up' like every other class:

MyOCXClass ocx = new MyOCXClass();

Adding a COM control to your .NET projects in VS.NET automatically creates a Runtime Callable Wrapper (RCW), which is what MyOCXClass is (assuming your OCX is named "MyOCX"). It also imports all the interfaces, enums, structs, etc. that are defined for the object(s).

jremignanti27-Oct-03 5:23

27-Oct-03 5:23

Has anyone noticed anything strange happening when you try to use the ref statement to pass a parameter while in a sub-thread?

Here's what I did:

<br />
public void ThreadProc()<br />
{<br />
    byte[] data=new byte[7];<br />
    data[0]=0;<br />
    data[1]=0;<br />
    data[2]=1;<br />
    data[3]=0;<br />
    data[4]=1;<br />
    data[5]=7;<br />
    data[6]=7;<br />
<br />
    chip1.WriteSPI(ref data[0], 7);<br />
}

where ThreadProc is called when I start a new thread:

<br />
thread1=new System.Threading.Thread(new ThreadStart(ThreadProc));<br />
thread1.Priority=System.Threading.ThreadPriority.Lowest;<br />
thread1.Start();

chip1.WriteSPI(ref byte datain, datasize) calls a COM object method that writes a stream of bytes on the USB port to a device downstream. It uses the reference as a pointer to the byte array.

All of this works fine in the main part of my app, but when I try to put it in a separate thread it writes garbage data to the port (actually it keeps writing the same garbage data every time). Has anyone done anything like this? Please feel free to point out my gross ignorance where appropriate.

Thanks
JR

Heath Stewart27-Oct-03 6:35

27-Oct-03 6:35

Is your COM object implemeneted as an STA or an MTA? If it's an STA, threading it can lead to unknown results. Marshalling could also be the culprit. If you're not marshalling the data correctly, its representation in the other context might not be correct and would produce garbage (right memory, wrong structure).

jremignanti27-Oct-03 8:00

27-Oct-03 8:00

My COM object is not implemented as an STA.
so if it's marshalling, what can I do? (I know there probably isn't a short answer)

thanks.

Heath Stewart27-Oct-03 8:05

27-Oct-03 8:05

Instead of importing the typelib automatically, you may have to define your own interface in .NET (that which reflects the class interface of your OCX), putting the appropriate marshaling attributes (MarshalAsAttribute). See that class (and the System.Runtime.InteropServices namespace for more details (and it'd be good to take a quick glance before proceding).

Question, though. Are you trying to pass the first byte array element as a reference, or do you want to pass the entire array. The way you're doing it means that you're passing the address of the first element and this will definitely requiring marshaling. If you want to pass the whole array as a ref, use ref myByteArray as a parameter instead. .NET will take care of a lot of things for you, including stuff like this.

jremignanti27-Oct-03 8:28

27-Oct-03 8:28

I want to pass the entire array, but what data type will my COM object be expecting if I pass ref bytearray?
right now, the prototype for my COM method is:
STDMETHODIMP CUSB::WriteSPI(unsigned char* datain, int size)
so, when C# gets a hold of that, it takes the pointer as a ref byte
in other words, what is the C++/COM equivalent of a ref to an array?

Heath Stewart27-Oct-03 8:34

27-Oct-03 8:34

First, an array is always a reference type. While some examples use ref with arrays, it's really only necessary for value types (int, long, byte, etc.) Passing a reference type results in the address passed to the native function.

For your interface, though, you'd want to write your method to that functions like so:

[Guid("...")]
public interface IUSB
{
  void WriteSPI(
    [MarshalAs(UnmanagedType.LPArray,SizeParamIndex=1)]byte[] array,
    int size);
  // ...
}

This will marshal the array as the address to the first element, which is what you're wanting to do.

jremignanti27-Oct-03 9:02

27-Oct-03 9:02

I understand, but C# still sees the unsigned char* from my COM method as a ref byte so how can I get around that?
sorry to keep bugging you.

Heath Stewart27-Oct-03 10:08

27-Oct-03 10:08

Hmm, it's usually right...but not always the easiest to implement. It would make sense, since ref'ing the first element would return the address of the array, but as you can see...it's not working. Cry | :((

What I was referring to was actually defining the interface yourself and not using the interop assembly that's generated automatically. Especially for small typelibs or for typelibs which you only need a couple of things (like many do for mshtml's typelib), it's just easier defining the interface with the right attributes and method placements (for IUnknown interfaces, order of the methods is important; for IDispatch interfaces, using the DispIdAttribute with the correct ID is important). You can still instantiate the COM object through the interop, or derive a class from AxHost and override the necessary things, also implementing your interface, or using various methods in the Marshal class or Type class, and set the reference to a variable defined as your class interface. Access the methods from the interface (as in all COM you should, anyway).

Still, though, that method signature should be right. When you say jibberish, what exactly do you mean?

jremignanti27-Oct-03 10:36

27-Oct-03 10:36

When I said it was putting out garbage data, when I call
WriteSPI(dataarray, size) I was looking at the output in bytes and I would get:
00 00 AA 00 size 00 ...
so the size value was being sent in the part that was supposed to be the data, the first three bytes of data was always the same though, no matter what I sent.

Are you saying that I can write a separate interface for my COM object in C#, that will override the one that was automatically generated when I compiled the C++ code for the COM object?
If so, I didn't realize you can do that. If I specify the GUID as an attribute for the object, it will be able to find it?
hmmmm...

Heath Stewart27-Oct-03 10:43

27-Oct-03 10:43

This definitely sounds like a marshaling problem. Seems like data about the array is being sent when you want the array data since the bytes should be the same on both.

You shoud read Advanced COM Interop in the MSDN Library. Basically, you're interface is just a way to access the class. In COM, you treat every object through it's interface by QI'ing (QueryInterface) for the interface that the class implements. In .NET this is acheived by merely casting.

You can define the interface in your project regardless of what is in the interop assembly, yes. As long as the method signatures are marshalable and similar (proper number of params) and use the same return types (should all be void unless PreserveSignature is true, which then you use int to represent an HRESULT). Just instantiate your COM class and cast it to the interface you redefined (remember, use the same GUID for the interface in the GuidAttribute and keep all that stuff the same I said in the previous post) and you should have a valid reference to your object through that interface (again, it's like calling QI, which doesn't care about qualified names like .NET does).

I'm not sure I'm explaining this as easily as possible, but read that section in MSDN (or perhaps start with the more basic stuff that comes before it). COM interop is powerful but is also is a beast to tame.

jremignanti27-Oct-03 10:54

27-Oct-03 10:54

okay, I get it...
Thanks a lot for your help.
just one last question, for my new interface, do I use the GUID from the COM interface or from the COM class itself?

that's it, I swear.
thanks again.

Jesse

Heath Stewart27-Oct-03 10:55

27-Oct-03 10:55

The interface.

jremignanti27-Oct-03 11:17

AllowDrop Property Problem

27-Oct-03 11:17

arrrrrgggggghh...
Using the interface works fine, except when it is in my new thread.
damn.

Volker Jacobsen27-Oct-03 3:14

Volker Jacobsen

27-Oct-03 3:14

Hi
In my Application I can't set the AllowDrop Property of any component to true. I allways get the runtime error Drag&Drop registration failed.

My application is an MDI Container with two ListViews ,one TreeView and a login-window, that is loaded the actual Form.

The error also happends, when I try to load an MDI Child with a ListView and the AllowDrop Property on true.

I am not so long in C# so maybe I just missed some important detail. But I can't find it.

Thanks for your help

Re: AllowDrop Property Problem

Heath Stewart27-Oct-03 8:44

Re: AllowDrop Property Problem

27-Oct-03 8:44

This is a threading problem. "Drag&Drop" registration includes a call to OleInitialize, which must be called on an STA (which all processes should be anyway). What does this mean? Well, first take a look at the STAThreadAttribute. Apply that to your entry point (Main). Second, and in some cases*, you may have to call Thread.CurrentThread.ApartmentState = ApartmentState.STA before calling Application.Run (starts your application message pump):

public class MyApp : Form
{
  private MyApp()
  {
  }
  [STAThread]
  public static void Main()
  {
    Thread.CurrentThread.ApartmentState = ApartmentState.STA;
    Application.Run(new MyApp());
  }
}

* Those rare cases happen when the application is invoked in an MTA, like Internet Explorer invoking the app via IEExec.exe for Internet-deployed, touchless installations. The STAThreadAttribute does not seem to affect the runtime, so I had to include that one-liner hack.

Volker Jacobsen27-Oct-03 20:46

Volker Jacobsen

27-Oct-03 20:46

Thank you. Now it works. Smile | :)

Two ImageList and two ImageIndex (and maybe... useful source code for you)

god4k27-Oct-03 1:36

god4k

27-Oct-03 1:36

Hello, Sir
I have two ImageList and two ImageIndex as the code below.
My problem is indexA and indexB show the same list of images.
How to make the indexA show list of image in _imagelistA
and make the indexB show list of image in _imagelistB ?

Thank You.
Sorry for bad English.

public ImageList imagelistA
{
get { return _imagelistA;}
set { _imagelistA = value; }
}
[TypeConverter(typeof(ImageIndexConverter)), Editor("System.Windows.Forms.Design.ImageIndexEditor, System.Design,Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a",typeof(System.Drawing.Design.UITypeEditor))]
public int indexA
{
get { return _indexA; }
set { _indexA = value; }
}

public ImageList imagelistB
{
get { return _imagelistB;}
set { _imagelistB = value; }
}
[TypeConverter(typeof(ImageIndexConverter)), Editor("System.Windows.Forms.Design.ImageIndexEditor, System.Design,Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a",typeof(System.Drawing.Design.UITypeEditor))]
public int indexB
{
get { return _indexB; }
set { _indexB = value; }
}

Re: Two ImageList and two ImageIndex (and maybe... useful source code for you)

Heath Stewart27-Oct-03 2:37

How do I catch Windows messages in c#??

27-Oct-03 2:37

If you mean in code, simple:

Image imgA = imageListA.Images[indexA];
Image imgB = imageListB.Images[indexB];

If you mean through the designer, you'll have to create your own TypeConverter (or derive from ImageIndexConverter) and return the image indeces from the currect ImageList, meaning that you'll have to use two separate TypeConverters.

See the docs about the TypeConverter.GetStandardValues method for clues on how to do this, or take a look at System.Windows.Forms.ImageIndexConverter through some disassembler (like ildasm.exe that comes with the .NET Framework SDK) or decompiler (like .NET Reflector).

IrishSonic27-Oct-03 0:03

IrishSonic

27-Oct-03 0:03

How do I catch windows messages in c#??

In MFC, I would do this:

// to catch windows messages
MSG msg;
while( PeekMessage( &msg,NULL,0,0,PM_REMOVE ) )
{
TranslateMessage( &msg );
DispatchMessage( &msg );
}

Thanks.

Re: How do I catch Windows messages in c#??

Heath Stewart27-Oct-03 2:13