Variants in .net - C# Discussion Boards

16-May-02 13:21

Hi' how are you.

I'm having some trouble with an ActiveX Control which i use in a project i'm working on.

The Control has a method like this:

Ax.GetCurrentImage(ref variant image, ref variant size)

Where the image parameter is supposed to return a bitmap.
And the size parameter returns the size of the bitmap.

I've tryed going in the direction of using a variable of the type System.Object, but that doesen't work.

If anyone has some ideas on how to attack this problem i would be grateful.

I'll try and post some more concrete code and error messages tomorrow when i get to work.

Venlig hilsen / Regards

Steffen Otto Jensen
(Denmark)

Rama Krishna Vavilala16-May-02 14:35

Rama Krishna Vavilala

16-May-02 14:35

Did you not use AxImp tool or use IDE to add the ActiveX control. Variants are automatically converted to objects.

ElCortez16-May-02 20:51

16-May-02 20:51

Hi' and thanks for your reply.

Yes i did import the control with the AxImp tool.
The code that is giving me trouble is the following:

object bmp = new System.Object();
object size = new System.Object();

ax.GetBMP(ref bmp, ref size);

** pictureBox1.Image = (Bitmap)bmp;

** The exception gets thrown on this line, and sounds like this:
an unhandled exception of type System.InvalidCastException occured in WindowsApplication2.exe
Additional information: Specified cast is not valid.

The "blueprint" for the method looks like this:
ax.GetBmp(ref object vimage, ref object vsize)

And in the documentation for the ActiveX Control the two parameters of the GetBMP method is listed af Variant types.
Holding that together with this table from the framework SDK i guess the variant type is not completely supported:
TypeCode COM variant type
----------------------------------------
TypeCode.Empty --> VT_EMPTY
TypeCode.Object --> VT_UNKNOWN
TypeCode.DBNull --> VT_NULL
TypeCode.Boolean --> VT_BOOL
TypeCode.Char --> VT_UI2
TypeCode.Sbyte --> VT_I1
TypeCode.Byte --> VT_UI1
TypeCode.Int16 --> VT_I2
TypeCode.UInt16 --> VT_UI2
TypeCode.Int32 --> VT_I4
TypeCode.UInt32 --> VT_UI4
TypeCode.Int64 --> VT_I8
TypeCode.UInt64 --> VT_UI8
TypeCode.Single --> VT_R4
TypeCode.Double --> VT_R8
TypeCode.Decimal --> VT_DECIMAL
TypeCode.DateTime --> VT_DATE
TypeCode.String --> VT_BSTR
Not supported. --> VT_INT
Not supported. --> VT_UINT
Not supported. --> VT_ARRAY
Not supported. --> VT_RECORD
Not supported. --> VT_CY
Not supported. --> VT_VARIANT

Or am i just confused..

I hope to get some input back

Venlig hilsen / Regards

Steffen Otto Jensen
(Denmark)

Gaul21-May-02 4:34

Gaul

21-May-02 4:34

Try to create an actual bitmap object and see if it works, like this:

Bitmap bmp = new System.Drawing.Bitmap();
int size = 0;
ax.GetBMP(ref bmp, ref size);

pictureBox1.Image = (Bitmap)bmp;

Gaul C. Ihenacho
Gaulles Technologies, Inc
http://www.gaulles.com

ElCortez21-May-02 12:11

21-May-02 12:11

Bad luck.

when i use your suggestion:

Bitmap bmp = new System.Drawing.Bitmap(352, 288);
int size = 0;
axImage1.GetBMP(ref bmp, ref size);
pictureBox1.Image = (Bitmap)bmp;

I get the folowing error messages:

* The best overloaded method match for 'AxATLCAMIMAGELib.AxCamImage.GetBMP(ref object, ref object)' has some invalid arguments

* Argument '1': cannot convert from 'ref System.Drawing.Bitmap' to 'ref object'

* Argument '2': cannot convert from 'ref int' to 'ref object'

But thanks for your help.

Im not sure what i should do now... Confused | :confused:

Venlig hilsen / Regards

Steffen Otto Jensen
(Denmark)

Rama Krishna Vavilala21-May-02 12:30

Rama Krishna Vavilala

21-May-02 12:30

I see that this problem is not yet solved.

What are you returning the Variant as VT_DISPATCH? Can you post a bit of implementation of your COM method GetImage.

ElCortez21-May-02 13:05

21-May-02 13:05

Unfortunatly i can't do that, as i didn't implement it, the control is supplied by the manufacturer of a camera.

The only documantation i have about it is the following:

GetBMP Method:

Description:
Returns the data and size of the current bitmap image.

Syntax:
CamImage.GetBMP Image, Size

Part Description
Image: Required. A variant containing the bitmap data.
Size: Required. Contains the size of the returned bitmap data.

Remarks:
Returns the data and size of the current bitmap image. The Display property has to be set to True when using the GetBMP method, otherwise the Jpeg images won’t be decompressed to bitmaps.

Example:
In this example a bitmap is captured with the GetBMP method and saved to a file.
Dim b As Variant
Dim Size As Variant
Dim a() As Byte
Call CamImage1.GetBMP(b, Size)
a() = b
Open "C:/Test.bmp" For Binary Access Write As #1
Put #1, , a()
Close #1

I hope this is helpfull!

I appreciate your help.

Venlig hilsen / Regards

Steffen Otto Jensen
(Denmark)

Rama Krishna Vavilala21-May-02 14:46

Rama Krishna Vavilala

21-May-02 14:46

This is what you do

object bmp = new System.Object();
object size = new System.Object();

ax.GetBMP(ref bmp, ref size);

System.IO.MemoryStream ms = new System.IO.MemoryStream((byte[])bmp);
System.Drawing.Bitmap image = new System.Drawing.Bitmap(ms);

ElCortez22-May-02 2:15

String handling book excerpt

22-May-02 2:15

Thanks Rama Krishna

The code you gave me was Paste'n'Run.

That helped me a lot!

Venlig hilsen / Regards

Steffen Otto Jensen
(Denmark)

Tom Archer16-May-02 5:37

16-May-02 5:37

For those of you who've not seen it, I've uploaded part 1 of a chapter excerpt from my Inside C# book. This particular part is based on a topic I see frequently asked about - string handling in C# - and I believe covers many areas and issues not found in the online documentation and other texts.

Enjoy and please feel free to drop me a line regarding the article/chapter and even how it can be improved!

Cheers,
Tom Archer
Author - Inside C#, Visual C++.NET Bible

Rickard Andersson²⁰16-May-02 7:15

Rickard Andersson²⁰

16-May-02 7:15

Thats good!
And helpful! Thank you man! Smile | :)

Rickard Andersson@Suza Computing
ICQ#: 50302279 (Add me!)
E-mail: nikado@pc.nu
I'm from the winter country SWEDEN!

Albert Pascual16-May-02 7:19

Albert Pascual

16-May-02 7:19

When is Visual C++ .NET Bible available?

Tom Archer16-May-02 7:16

16-May-02 7:16

Thanks for the interest, Albert!

That book is being "processed" now. In other words, I'm done with my work and the publisher is printing it. That usually takes about 2 months to get to the store.

Cheers,
Tom Archer
Author - Inside C#, Visual C++.NET Bible

Albert Pascual16-May-02 7:30

Albert Pascual

16-May-02 7:30

Cool!

So, should I buy it? Duh! I am asking the Author Smile | :)

Anything different from Step by Step Visual C++ .NET? How long it took you to write the book?

Tom Archer16-May-02 7:30

16-May-02 7:30

Albert Pascual wrote:
So, should I buy it? Duh! I am asking the Author

Actually, I'm very forthcoming and will tell you exactly whether or not you should buy the book based on your needs. Remember, it doesn't do me any good to sell someone a book that they don't like, will probably return and certainly not have nice things to say about.

Having said that, it doesn't look like the book is for you as the book you're comparing it to is a managed extensions book and mine is an MFC book.

Therefore, if you're looking for a beginner-level managed extensions book, I'd recommend the Step by Step. I don't know of any decent intermediate-to-advanced managed extensions books. On the other hand, if you're looking for a really good MFC book, then I would recommend mine without hesitation.

Cheers,
Tom Archer
Author - Inside C#, Visual C++.NET Bible

Albert Pascual16-May-02 7:43

Albert Pascual

16-May-02 7:43

Thanks Tom,

Actually I am moving away from any MFC. I only use MC++ extensions and C# for UI (I use Inside C# as a reference)

Even that I think I am going to buy your book when it comes out, if is just as good as your Inside C# I am going to enjoy reading it!

Thanks
Al

Tom Archer16-May-02 7:38

16-May-02 7:38

Albert Pascual wrote:
I use Inside C# as a reference

Thank you very much for the support. Have you seen the second edition yet?

Albert Pascual wrote:
Even that I think I am going to buy your book when it comes out, if is just as good as your Inside C# I am going to enjoy reading it!

Definitely the MFC book is very strong. While there will be a lot of beginner level material (no way a pub will let anyone write just an advanced MFC book for some reason), it also has tons of great material not found in any other MFC book. I think you'll get a lot out of it.

Cheers,
Tom Archer
Author - Inside C#, Visual C++.NET Bible