Introduction
During discussions in forums, I come across many people who want to write COM/ATL DLL, but don't know how to create properties, methods or raise events from component or strive for fundamental knowledge to create them. For them, I had written this article in VC++ 6.0. Since Visual Studio 6 is now out of support, many beginners requested me for the same article using Visual Studio 2005/2008 as there is much GUI difference between the two.
So, I am presenting the same article using Visual Studio 2005 and as it’s a new article, I have to provide readers with something new, otherwise they will reject this article. .NET application is slowly eating into Visual C++ share of applications. So to follow popular demand, I will show how to use COM component in .NET application instead of Unmanaged Application. As it is a beginner article, I am included a few extra screenshots in the article. Please don't flame for using the same.
Table of Contents
- Creating ATL Component
- Using it in Visual C# Application (.NET 2005)
Creating ATL Component
Let us go step by step to create an ATL component in Visual Studio 2005:
- Open Visual Studio 2005, and Click on File| New | Project menu, which will show you the following File-Save dialog box, where you can provide a name for your new project. Here I put the name as
SimpleATLCom
and it is advisable to choose the destination folder, where you want to create your project, otherwise it will clutter your Document Folder. Press OK to confirm your changes. This will create a blank ATL component.
Figure 1: File Open Dialog
Now, in the next dialog box (ATL Project wizard), choose default setting and press Finish. If you need MFC Support, check Support MFC checkbox.
Figure 2: ATL Project Wizard
Now insert ATL Object in Project which I will show in the next step.
- Choose Project | Add Class. The following dialog box will appear:
Figure 3: Add Simple ATL Object
Choose ATL|ATL Simple Object and Press ADD button.
- Enter new Interface name in ATL Simple Object Wizard. You will see rest of the details are auto filled by Visual Studio development environment when you begin typing the interface name. Also check the Connection Point check box in the Option Tab which provides component ability to fire events.
Figure 4: ATL Simple Object
Figure 5: Select Connection Point Check Box
-
Now if you check the following IDL (Interface Definition Language) will be generated and included into your project:
1. 2. 3. 4. 5.
6. import "oaidl.idl";
7. import "ocidl.idl";
8.
9. [
10. object,
11. uuid(8F4FEC76-F1F6-4D69-A2E8-FFF4F316C101),
12. dual,
13. nonextensible,
14. helpstring("ISimpleCom Interface"),
15. pointer_default(unique)
16. ]
17. interface ISimpleCom : IDispatch{
18. };
19. [
20. uuid(2CA18A17-D157-4D1E-A2C7-3D69EBD87250),
21. version(1.0),
22. helpstring("SimpleATLcom 1.0 Type Library")
23. ]
24. Library SimpleATLcomLib
25. {
26. importlib("stdole2.tlb");
27. [
28. uuid(85D35B5B-8DBF-4562-96B0-66A4C4718DD5),
29. helpstring("_ISimpleComEvents Interface")
30. ]
31 dispinterface _ISimpleComEvents
32 {
33. properties:
34. methods:
35. };
36. [
37. uuid(A7657FC5-D63C-49C3-AEE5-D8799F412C74),
38. helpstring("SimpleCom Class")
39. ]
40. coclass SimpleCom
41. {
42 [default] interface ISimpleCom;
43. [default, source] dispinterface _ISimpleComEvents;
44. };
45. };
- At Line 11: This is default UUID (Unique ID) generated by Dev environment, this makes the component uniquely identifiable.
- At line 17: That’s our component name and UUID, its contents can be used to uniquely identify a component, you can use this id to create component.
- At Line 31: Our dis-interface i.e. event function.
- Now Add Property and method using Add Property and Add Method Wizard. This can be found in class view, right click on ISimpleCom interface then ADD->Add Method or Add Property:
Figure 6: Add Method/Add Property
Add method Calculate with Long as OUT, RETVAL parameter like this:
Figure 7: Add Method
Add Property ComMark of type Long as shown in the example:
Figure 8: Add Property
Similarly add property AtlMarks as long and StudentName as BSTR yourself. Sorry I forgot to mention about IN, OUT and RETVAL type in parameter.
Propget
– stands for property for getting the value from Component
PropPut
– stands for property for putting property to Component. This can be optional and if you remove it, this can make your property readonly
Method
— simple function to perform some calculation
[in]
- means data is going in or you are putting some value to Component
[out,retval]
- Notation states that argument using this will return with data
HRESULT
- Standard Error reporting variable
- Now add Event almost in the same way, we add method in interface. Now right click on
_ISimpleComEvents
and Add | Add method.
Figure 9: Add Event
-
Once everything is done, modified IDL File would look like this:
1. interface ISimpleCom : IDispatch
2. {
3. [id(1), helpstring("method Calculate")] HRESULT Calculate([out,retval]
4. LONG* a_lTotalMarks);
5. [propget, id(2), helpstring("property ComMarks")] HRESULT ComMarks([out,
6. retval] LONG* pVal);
7. [propput, id(2), helpstring("property ComMarks")] HRESULT ComMarks([in]
8. LONG newVal);
9. [propget, id(3), helpstring("property AtlMarks")] HRESULT AtlMarks([out,
10. retval] LONG* pVal);
11. [propput, id(3), helpstring("property AtlMarks")] HRESULT AtlMarks([in]
12. LONG newVal);
13. [propget, id(4), helpstring("property StudentName")]
HRESULT StudentName([out,
14. retval] BSTR* pVal);
15. [propput, id(4), helpstring("property StudentName")]
HRESULT StudentName([in]
16. BSTR newVal);
17. };
18.
19. dispinterface _ISimpleComEvents
20. {
21. properties:
22. methods:
23. [id(1), helpstring("method TotalMarks")] HRESULT TotalMarks([in] LONG
24. a_lTotalMark);
25. };
- Now add connection points into the main interface. For adding it, right click on CSimpleCom and click ADD | Add Connection Point. The following screenshot will appear:
Figure 10: Chose Add Connection Point
Choose > button to move _ISimpleComEvents source interface to implement connection point and click on finish. A new function Fire_TotalMarks is added to CSimpleCom class which can be used to raise event.
Figure 11: Add Connection Wizard
-
Now code all properties and functions present in CSimpleCom
class, i.e. Add Class Variable for ComMarks
, ATLMarks
and StudentName
for storing information coming from the outer world. After coding, our class would look like this:
1. 2. long m_lComMarks,m_lAtlMarks;
3. CComBSTR m_bstName;
4.
5. 6. STDMETHODIMP CSimpleCom::Calculate(LONG* a_lTotalMarks)
7. {
8. long lTotalMarks = m_lAtlMarks + m_lComMarks;
9. * a_lTotalMarks = lTotalMarks;
10. Fire_TotalMarks(lTotalMarks); 11. return S_OK;
12. }
13. 14. STDMETHODIMP CSimpleCom::get_ComMarks(LONG* pVal)
15. {
16. * pVal = m_lComMarks;
17. return S_OK;
18. }
19. 20. STDMETHODIMP CSimpleCom::put_ComMarks(LONG newVal)
21. {
22. m_lComMarks = newVal;
23. return S_OK;
24. }
25. 26. STDMETHODIMP CSimpleCom::get_AtlMarks(LONG* pVal)
27. {
28. * pVal = m_lAtlMarks;
29. return S_OK;
30. }
31. 32. STDMETHODIMP CSimpleCom::put_AtlMarks(LONG newVal)
33. {
34. m_lAtlMarks = newVal;
35. return S_OK;
36. }
37. 38. STDMETHODIMP CSimpleCom::get_StudentName(BSTR* pVal)
39. {
40. *pVal = m_bstName.Copy();
41. return S_OK;
42. }
43. 44. STDMETHODIMP CSimpleCom::put_StudentName(BSTR newVal)
45. {
46. m_bstName = newVal;
47. return S_OK;
48. }
Now Build the solution, your DLL would be registered automatically, when the build process is over.
Using it in Visual C# Application
Now again move forward step by step to create a project in C#.NET and include support of COM component in project.
- Add a new C# Window application Project (
SimpleATLcomTest
) in the same solution and click to accept default configuration to create a test project.
Figure 12: Add a New C# Project
-
Design the interface as shown in the screenshot given below; add three Textbox
es for putting values into the Component and four boxes for retrieving all values including the calculated value.
Figure 13: Test Application Design
-
Now, add a reference for SimpleATLCom.dll into your project, by right clicking on Project name and clicking on Add Reference menu item.
Figure 14: Add Reference Menu
Click on COM Tab item and select SimpleATLCom.dll to add reference of Component into the project.
Figure 15: Add Reference
-
Now, write the following code to use the component into your project.
1. 2. using SimpleATLcomLib;
3. namespace SimpleAtlComTest
4. {
5. public partial class SimpleATLCom : Form
6. {
7. 8. ISimpleCom objSimpleCom = new SimpleComClass();
9. 10. _ISimpleComEvents_Event event1 = null;
11. public SimpleATLCom()
12. {
13. InitializeComponent();
14. 15. event1 = (_ISimpleComEvents_Event)objSimpleCom;
16.
17. 18. event1.TotalMarks += new _ISimpleComEvents_TotalMarksEventHandler
(ISimpleCom_TotalMarksEvent);
19.
20. }
21. 22. private void btnPutValues_Click(object sender, EventArgs e)
23. {
24. objSimpleCom.AtlMarks = int.Parse(txtPATLMarks.Text);
25. objSimpleCom.ComMarks = int.Parse(txtPComMarks.Text);
26. objSimpleCom.StudentName = txtPName.Text;
27. }
28. 29. 30. private void btnGetDetails_Click(object sender, EventArgs e)
31. {
32. txtGAtlMarks.Text = objSimpleCom.AtlMarks.ToString();
33. txtGComMarks.Text = objSimpleCom.ComMarks.ToString();
34. txtGName.Text = objSimpleCom.StudentName;
35. objSimpleCom.Calculate();
36. }
37. 38. void ISimpleCom_TotalMarksEvent(int lTotalMarks)
39. {
40. txtTotalMarks.Text = lTotalMarks.ToString();
41. MessageBox.Show("Total Marks is " + txtTotalMarks.Text);
42. }
43. }
44. }
- Run the Test application, and you will see the result:
Figure 16: Running Application
About the Download Code
Source Code Includes
- SimpleAtlCom.dll (with source code)
- Test Project in Visual C#
Using of Demo Application
If you like, use the Com DLL and Test application first. Don't forget to register Com DLL, i.e., SimpleAtlCom.dll, to your computer. You can use this command line to register the Component.
Drive:> %sys%regsvr32 path_to_dll\SimpleAtlCom.dll
Author Comment
I tried my level best to tell each and every simple aspect of com DLL. If it is missing something, feel free to contact me or leave your precious comments in the discussion forum below.
Special Thanks
- To my mother (Late) and father and off course my wife
- To CodeProject.com, for providing a platform for Programmer Interaction.
- To Leeland Clay for correcting editing mistake(s) and providing suggestion(s) for improvement.
History
- 18th July, 2009: Initial post