Programming Excel with VBA and .NET : Tasks in Visual Basic - Run Other Applications

CreateObject and GetObject work only with Windows applications that have support for ActiveX automation built in to them. Most Microsoft products and many other Windows products support that type of automation, which is sometimes also called OLE automation .

ActiveX or OLE automation allows you to use the internal objects, properties, and methods of the application in the same way that you control Excel from Visual Basic. For example, the following code starts Microsoft Word from Excel, creates a new document, inserts some text, and saves the file:

    Sub UseWord( )
        Dim word As Object, doc As Object
        Set word = CreateObject("Word.Application")
        ' Show Word (otherwise it's invisible).
        word.Visible = True
        ' Create document.
        Set doc = word.Documents.Add
        ' Insert some text
        doc.Range.InsertAfter "Some text to insert."
        ' Save the file
        doc.SaveAs ThisWorkbook.Path & "\StartWord.doc"
    End Sub

You can use GetObject to get a running instance of an application. For example, the following code uses a running instance of Word to open the document created by the preceding code:

    Sub GetWord( )
        Dim word As Object, doc As Object
        ' Get a running instance of Word.
        Set word = GetObject(, "Word.Application")
        ' Open a document.
        Set doc = word.documents.Open(ThisWorkbook.Path & "\StartWord.doc")
        word.Visible = True
    End Sub

In the preceding code, GetObject fails if Word is not already running. You can use GetObject with a filename to start the application associated with the file if it is not already running, as shown here:

    Sub GetDocument( )
        Dim word As Object, doc As Object
        ' Get the demo document whether or not is it open.
        Set doc = GetObject(ThisWorkbook.Path & "\StartWord.doc")
        ' Show the document.
        doc.Application.Visible = True
    End Sub

In this case, GetObject starts Word if it is not already running and loads the document. If Word is running or if the document is already open, the code just returns a reference to that object without starting a new instance.

Both CreateObject and GetObject do something called late binding . Late binding means that the type of the object is not checked until the application is running. It's often better to use early binding , since that allows Visual Basic to check that types match when the code is compiled, which helps correct type-mismatch errors.

Early binding requires that you add a reference to the library for the application you want to use from Excel. To add a reference to an application in Visual Basic:

There may be quite a few libraries installed on your computer, and sometimes it is difficult to find the one you want. Microsoft groups most of its libraries under the company name so they sort together, and most other companies do the same.

Once you have added a reference to another application, you can use objects from that application in the same way that you use Excel objects. For example, the following code creates a new document in Word and inserts some text:

    ' Requires reference to Microsoft Word object library.
    Sub EarlyBinding( )
        Dim doc As New Word.Document
        doc.Range.InsertAfter "This is early-bound."
        doc.Application.Visible = True
    End Sub

One of the key advantages of using explicit types, such as Word.Document, is that it enables Visual Basic's Auto Complete features to help you navigate through the various objects, properties, and methods that an application provides. Figure 2 shows the Auto Complete feature in action for the Word objects.

Figure 2. References and explicit types enable Auto Complete

Table 2 lists some common applications that provide ActiveX objects you can use from Visual Basic. Be aware that most of these applications provide a very complex set of objects that may be organized differently from Excel's objects. Using the objects from other applications often requires a good deal of research and learning.

Not all applications support ActiveX, however. Some of the simple (and common) applications can be started only with the Shell function. Shell runs the application using its filename and returns a nonzero number if the application started successfully. You can combine Shell with SendKeys to automate applications in a simple way:

    Sub StartNotepad( )
        Dim id As Integer
        id = Shell("notepad.exe", vbNormalFocus)
        ' If id is not zero, then Shell worked. This is some text to insert
        If id Then
            SendKeys "This is some text to insert", True
            SendKeys "^s", True
            SendKeys ThisWorkbook.Path & "\StartNote.txt", True
            SendKeys "~", True
        End If
    End Sub

The preceding code starts Notepad, inserts some text, and saves the file. You can send keystrokes to only the application that currently has focus in Windows. If the user changes the focus while your code is running, the keystrokes may go to the wrong application. This makes debugging the preceding code very difficult. If you try to step through the code, the keystrokes are sent to the Code window, rather than to Notepad!

You can switch the focus to another application using the AppActivate function. AppActivate uses the text displayed in the window's titlebar to select the window to grant focus. If you run the preceding code, the Notepad window will contain the text "StartNote.txt — Notepad", so the following code will switch focus to that window to make some changes:

    Sub GetNotepad( )
					
					
					 

        Dim id As Integer
        On Error Resume Next
        AppActivate "StartNote.txt - Notepad", True
        If Err Then MsgBox ("StartNote.txt is not open."): Exit Sub
        SendKeys "{end}", True
        SendKeys ". Some more text to insert.", True
        SendKeys "^s", True
    End Sub

You can also use the ID returned by the Shell function with AppActivate to activate a running application. SendKeys uses the predefined codes listed in Table 3 to send special keys, such as Enter or Page Up, to an application.

I should point out here that Excel provides methods for running two of the most commonly used applications. Use the FollowHyperlink method to display a web page in the default browser or to create a new email message. Use the SendMail method to send a workbook as an attachment. The following code demonstrates these different approaches:

    Sub BrowserAndMail( )
        ' Starts browser and displays page.
        ThisWorkbook.FollowHyperlink "http://www.mstrainingkits.com"
        ' Creates a new, blank mail message
        ThisWorkbook.FollowHyperlink "mailto:[email protected]"
        ' Sends the workbook as an attachment without displaying message.
        ThisWorkbook.SendMail "[email protected]"
    End Sub