Accessing a Remote Object

With Visual Basic, accessing a remote object requires only that the program declare an object variable and assign the return of a New statement to the variable. The following is the syntax for the statements:

Dim ObjectVar As InterfaceName
Set ObjectVar = New CoClassName

The Dim statement declares a variable of an interface type. The New keyword creates an instance of an object. Used together, the two declare and create an instance of an ActiveX object. For example:

Dim MyLines As ILines
Set MyLines = New Lines.Lines

The Dim statement declares the object variable MyLines of the interface type ILines. The Set statement assigns a new object of the component object class (coclass) Lines to the variable MyLines. When you use the Dim statement to set a variable to an interface type, subsequent uses of the variable will execute faster than with the generic Object syntax.

The New keyword applies only to creating coclasses of interface or dispinterface types. To create other types of objects, the variable must be declared with the Dim statement, and the CreateObject function used as follows:

Set ObjectVar = CreateObject(ProgID)

CreateObject creates an ActiveX object, based on the specified programmatic identifier (ProgID). The ProgID has the form:

AppName.ObjectName

The AppName is the name of the application, and the ObjectName identifies the type of object to create. For more information about ProgIDs, see "Registering the Application" in Chapter 2, "Exposing ActiveX Objects."

You can use the GetObject function to re-establish the reference to the most recently used object that corresponds to the Filename and AppName.ObjectName specification, as follows:

Set ObjectVar = GetObject("Filename", ProgID)

For example, if the ActiveX client needs an existing instance of an object instead of a new instance, it can use the GetObject function.

The Hello sample application, included in the Win32 Software Development Kit (SDK), displays a Hello message in response to a mouse click. You can add a simple form that accesses the Hello application's exposed object from another process.

    To add a form

1. Start Visual Basic.
2. Click Open Project on the File menu.
3. In the dialog box, click Vb.mak in the Sample directory.
4. In the Forms box, click View Form to see the form, or click View Code to see the Visual Basic code.

   ‘Module-level declarations
   Dim HelloObj As IHello
   
   Sub Form_load ( )
   Set HelloObj = New Hello.Hello
   End Sub
   
   Sub Invoke_SayHello_Method_Click ( )
   HelloObj.SayHello
   End Sub
   
   Sub Get_HelloMsg_Property_Click ()
   Debug.Print HelloObj.HelloMessage
   End Sub
   
   Sub Set_HelloMsg_Property_Click ( )
   HelloObj.HelloMessage = "Hello Universe"
   End Sub
   
   Sub SetVisible_Click ( )
   HelloObj.Visible = True
   End Sub
   

The Form_Load subroutine creates the Hello Application object. Other subroutines manipulate the Hello Application object through the Visible and HelloMessage properties and the SayHello method.

To program an object in Visual Basic, you need its class name and the names and parameters of its properties and methods. For the Hello sample application, you need to know the exact names of the SayHello method, and the Visible and HelloMsg properties, along with the types of their arguments. This information is provided in the documentation for many objects, such as those exposed by Microsoft Excel. You can also get the information by viewing the object's type library with an object browser, such as the one included in Visual Basic. A sample browser, Browse, is provided in the Win32 SDK.