![\"startvstudio\"](\"http:\/\/salzlechner.com\/dev\/wp-content\/uploads\/sites\/2\/2016\/02\/startvstudio.png\")
<\/a><\/p>\nOnce Visual Studio is started we need to create a new project<\/p>\n
<\/p>\n My preferred language is C# but you can do the same in Visual Basic of course. Select a Class Library project and type in a name and location<\/p>\n Visual Studio will create a project with an empty class called Class1 for you<\/p>\n First you want to rename your class and probably also the code file (Class1.cs) or simply delete the class1 file and add a new one with a proper name<\/p>\n Also at the top above\u00a0the class you will need to add a using statement for the\u00a0System.Runtime.InteropServices which will be needed to enable COM Interop<\/p>\n <\/p>\n In order to create and use this component we need two main parts.<\/p>\n A class implementing the functionality of our component and a so-called Interface that is\u00a0a contract\u00a0describing all the methods and properties that will be available in\u00a0an object created from this class<\/p>\n We already have an empty class now lets add an empty Interface definition<\/p>\n as you can see right above the class definition (inside the namespace declaration) we define a public interface<\/p>\n The next step is to tell Visual Studio about this interface. We can do this by using metadata. In that metadata we have to do the following<\/p>\n Whats a GUID?<\/p>\n A GUID is a globally unique identifier. It a 128-bit value generated from random numbers and most often displayed as 32 hexadecimals digits. COM uses GUIDs as unique identifiers for components<\/p>\n Where do we get these GUIDs. The beauty of GUIDs is that we can programatically generate them at any time. Visual Studio has a little utility built in to handle this task for us.<\/p>\n From the tools Menu select Create GUID<\/p>\n The Create GUID dialog will be shown. In this case we will need format #5. Select Format #5 and then click New GUID and then click copy to copy the new GUID to the clipboard<\/p>\n Now lets add the metadata<\/p>\n We add a line that tells Visual Studio to make this interface visible as a COM component<\/p>\n then the next line we add the GUID generated earlier. This is our interfaces unique identifier and will be used to register the interface.<\/p>\n The InterfaceType is defined as an IDispatch interface.<\/p>\n Now lets work on the implementation of our class<\/p>\n Our class needs to inherit from the interface. In addition we also need to add metadata to the class.<\/p>\n The class also needs to be set to ComVisible and we need another GUID for our class.<\/p>\n In addition we define the class interface type and assign a ProgId to our class<\/p>\n To make it easier on us we can tell Visual Studio to automatically register our component for COM Interop when the project is built<\/p>\n You can simply open the project build\u00a0properties and enable to Register for COM Interop option<\/p>\n You do not have to do the above step. You can also manually register the component using the REGASM utility. In order to register your component using REGASM simply start a Visual Studio command prompt as Adminstrator and execute the following<\/p>\n REGASM dllfilename.dll \u00a0\/tlb \/codebase<\/p>\n The codebase switch is not required nor should it be used when deploying but it makes life easier on the development machine<\/p>\n At this point our full source should look as follows<\/p>\n Now we build the project in Visual Studio which will build our component and register it for COM Interop<\/p>\n Now in our DataFlex project we can import the component<\/p>\n On the import Automation library dialog browse to the folder containing your dll and tlb file and select the tlb file created by\u00a0Visual Studio<\/p>\n Once selected the Studio will generate a DataFlex class package based on the interface published in our Visual Studio project<\/p>\n Create a new view to test the component<\/p>\n At the top of the view use our class and add a Button to the view<\/p>\n We can add our COM object to the view and then in the OnClick procedure of the button we can call the\u00a0CreateComObject method to instantiate the COM object<\/p>\n Of course at this point our class is somewhat boring so we need to add actual functionality to our class. Back to Visual Studio<\/p>\n Our first major\u00a0feature will be the Hello function. We want to function to accept a name as a parameter and then let it return a new string saying\u00a0something like ‘Hello name, how are you?’<\/p>\n In order to do this we need to do 2 things<\/p>\n First in the interface we add the declaration<\/p>\n as you can see above we declare a function called Hello that returns a string and accepts a string as a parameter<\/p>\n above the function declaration you can see a metadata line. We are assinging a DispId\u00a0of 1. The DispId is the numeric identifier for this method in the COM component.<\/p>\n This line is not required because Visual Studio can automate assignment of DispIds but we prefer controlling our own DispIds.<\/p>\n Next we need to implement the actual method<\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n\n
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