JDT
06-07-2001, 09:13 PM
ActiveX Dll Tutorial --- by JDT
This tutorial is designed for those who know nothing about creating ActiveX Dll components in VB6.
Skill level --------> Intermediate
Prerequisites ---> Basic understanding of programming concepts and working knowledge of VB6
Time --------------> About 15 minutes
--------First let’s get a brief understanding of what a Dll is and why we would use one.
Dynamic-link libraries (DLL) contain reusable functions and data. With the use of Dll files, you can store often used functions in a common place, link to it through code, and leverage its functionality in any of your applications without adding the common procedures to every application. There is a down side to Dll’s; it must be installed on the users pc for your application to access it. The up side is mostly felt in large-scale applications. A good example is the Windows OS. Us VB programmers link to Dlls all the time (API) to get the functionality we need. Dividing your large projects into smaller pieces using Dlls is a more efficient way to manage you projects and fixing bugs in functions is a lot easier to just replace a small Dll than replacing a several meg exe.
--------What is ActiveX?
ActiveX technology is based on the Component Object Model (COM). COM is Microsoft’s standard that defines how software components interact with each other. COM is an implementation of Object Oriented Programming (OOP) that is language independent, which is a feature known as interoperability. ActiveX Dll's run in-process (uses memory space in your app). Most importantly, VB does the real work for you. If you know VB6 then you are 95% of the way there.
With those crash course descriptions out of the way, lets get started.
--------Make the Dll
1. Start VB and select ActiveX Dll for the project type.
2. In the properties window for the Class (the only code window in the project), name it 'CSomeDll'. Note - this is not the project properties window and is the same as naming a form.
3. Select Project from the menu, select Project1 Properties from the drop down list, change the project name to 'SomeDll', and change the Project Description to 'This is a useless DLL'. This description will show up in the Object Browser and the References list and is VERY IMPORTANT.
4. Now lets add a method (Function) to the class. Lets just have this take a string for its parameter and return it spelled backwards. Of course this function already exists in VB, but it will suit the needs of this simple example.
4.1 Make a Public function named 'ReverseString' in the class module. It must be Public if you want it to be visible to your client applications.
Option Explicit
Public Function ReverseString(ByRef SomeString As String) As String
ReverseString = StrReverse(SomeString)
End Function
5. Lets compile it by selecting File, in the drop-down list select Make SomeDll.dll and choose a safe place to save it.
6. Save the project wherever you like and close it.
That’s it, the Dll is ready for a client application to use it.
--------Lets now make a client application to implement our newly made Dll.
1. Start VB and Select 'Standard Exe' for the project type.
2. Add one textbox named Text1 and one Command Button named Command1 to the form.
3. Now lets reference our Dll by selecting Project from the menu bar, then select References from the drop-down list. Now you need to scroll through the list and look for ---> 'This is a useless DLL' <--- That is the Project Description we gave our Dll in step 4 of creating the Dll. Put a check mark by it and click ok. If you don't see it, browse for it in the location you saved it in step 5 of creating the Dll (should be unnecessary though)
4. Now our client app knows about the library we want to link to but we still need to assign the class in the Dll to an object variable. So add this code to the general declarations section of your forms code module:
Dim X As CSomeDll
'CSomeDll' is the name of the class in the DLL that has the method we want to use. We named it this in step 2 of creating the Dll.
5. Now add this code to Command1:
Private Sub Command1_Click()
Set X = New CSomeDll '<---Assigns an object reference
Text1.Text = X.ReverseString(Text1)
Set X = Nothing '<--------Release resources to the object
End Sub
As you just seen (unless you pasted the code), VB provided Intellisense to the variable X and we see the method we added to the Dll's class object.
6. Run the program and click the button a few times to see it work.
That’s it. Simple enough yet very powerful when the situation mandates it.
--------What about registering the Dll?
VB automatically registered the component when you compiled the Dll. If you are to distribute this, you will need to use a good Installer (not PDW) to do it for you. To manually register this on a pc, from the command prompt type this ---> REGSVR32 C:\PathToTheDll.dll <--- and to unregister it, type this --->REGSVR32 /u C:\PathToTheDll.dll Note -- 'C:\PathToTheDll.dll' should be the actual path to the Dll file.
--------Some noteworthy stuff about ActiveX dlls
You can use a Group project while designing the Dll. Highly recomended
ActiveX exe's do the same as ActiveX Dll's except exe's run out of process (their own address space) and uses asynchronous notification.
ActiveX Dll's beat out ActiveX Exe's on performance
You can make a *real* Dll in VB and declare it like the API calls you might have used but this can't be done with ActiveX. ActiveX is much more preferable. Unless you know C, this is quite difficult,
JDT
This tutorial is designed for those who know nothing about creating ActiveX Dll components in VB6.
Skill level --------> Intermediate
Prerequisites ---> Basic understanding of programming concepts and working knowledge of VB6
Time --------------> About 15 minutes
--------First let’s get a brief understanding of what a Dll is and why we would use one.
Dynamic-link libraries (DLL) contain reusable functions and data. With the use of Dll files, you can store often used functions in a common place, link to it through code, and leverage its functionality in any of your applications without adding the common procedures to every application. There is a down side to Dll’s; it must be installed on the users pc for your application to access it. The up side is mostly felt in large-scale applications. A good example is the Windows OS. Us VB programmers link to Dlls all the time (API) to get the functionality we need. Dividing your large projects into smaller pieces using Dlls is a more efficient way to manage you projects and fixing bugs in functions is a lot easier to just replace a small Dll than replacing a several meg exe.
--------What is ActiveX?
ActiveX technology is based on the Component Object Model (COM). COM is Microsoft’s standard that defines how software components interact with each other. COM is an implementation of Object Oriented Programming (OOP) that is language independent, which is a feature known as interoperability. ActiveX Dll's run in-process (uses memory space in your app). Most importantly, VB does the real work for you. If you know VB6 then you are 95% of the way there.
With those crash course descriptions out of the way, lets get started.
--------Make the Dll
1. Start VB and select ActiveX Dll for the project type.
2. In the properties window for the Class (the only code window in the project), name it 'CSomeDll'. Note - this is not the project properties window and is the same as naming a form.
3. Select Project from the menu, select Project1 Properties from the drop down list, change the project name to 'SomeDll', and change the Project Description to 'This is a useless DLL'. This description will show up in the Object Browser and the References list and is VERY IMPORTANT.
4. Now lets add a method (Function) to the class. Lets just have this take a string for its parameter and return it spelled backwards. Of course this function already exists in VB, but it will suit the needs of this simple example.
4.1 Make a Public function named 'ReverseString' in the class module. It must be Public if you want it to be visible to your client applications.
Option Explicit
Public Function ReverseString(ByRef SomeString As String) As String
ReverseString = StrReverse(SomeString)
End Function
5. Lets compile it by selecting File, in the drop-down list select Make SomeDll.dll and choose a safe place to save it.
6. Save the project wherever you like and close it.
That’s it, the Dll is ready for a client application to use it.
--------Lets now make a client application to implement our newly made Dll.
1. Start VB and Select 'Standard Exe' for the project type.
2. Add one textbox named Text1 and one Command Button named Command1 to the form.
3. Now lets reference our Dll by selecting Project from the menu bar, then select References from the drop-down list. Now you need to scroll through the list and look for ---> 'This is a useless DLL' <--- That is the Project Description we gave our Dll in step 4 of creating the Dll. Put a check mark by it and click ok. If you don't see it, browse for it in the location you saved it in step 5 of creating the Dll (should be unnecessary though)
4. Now our client app knows about the library we want to link to but we still need to assign the class in the Dll to an object variable. So add this code to the general declarations section of your forms code module:
Dim X As CSomeDll
'CSomeDll' is the name of the class in the DLL that has the method we want to use. We named it this in step 2 of creating the Dll.
5. Now add this code to Command1:
Private Sub Command1_Click()
Set X = New CSomeDll '<---Assigns an object reference
Text1.Text = X.ReverseString(Text1)
Set X = Nothing '<--------Release resources to the object
End Sub
As you just seen (unless you pasted the code), VB provided Intellisense to the variable X and we see the method we added to the Dll's class object.
6. Run the program and click the button a few times to see it work.
That’s it. Simple enough yet very powerful when the situation mandates it.
--------What about registering the Dll?
VB automatically registered the component when you compiled the Dll. If you are to distribute this, you will need to use a good Installer (not PDW) to do it for you. To manually register this on a pc, from the command prompt type this ---> REGSVR32 C:\PathToTheDll.dll <--- and to unregister it, type this --->REGSVR32 /u C:\PathToTheDll.dll Note -- 'C:\PathToTheDll.dll' should be the actual path to the Dll file.
--------Some noteworthy stuff about ActiveX dlls
You can use a Group project while designing the Dll. Highly recomended
ActiveX exe's do the same as ActiveX Dll's except exe's run out of process (their own address space) and uses asynchronous notification.
ActiveX Dll's beat out ActiveX Exe's on performance
You can make a *real* Dll in VB and declare it like the API calls you might have used but this can't be done with ActiveX. ActiveX is much more preferable. Unless you know C, this is quite difficult,
JDT