Visual Basic 6 Black Book:OLE
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Chapter 26OLE


If you need an immediate solution to:
Adding An OLE Control To A Form
Creating And Embedding An OLE Object At Design Time
Linking Or Embedding An Existing Document At Design Time
Autosizing An OLE Control
Determining How An Object Is Displayed In An OLE Container Control
Using The OLE Control’s Pop-Up Menus At Design Time
Inserting An OLE Object Into An OLE Control At Runtime
Deactivating OLE Objects
Using Paste Special To Insert A Selected Part Of A Document Into An OLE Control
How To Activate The OLE Objects In Your Program
Activating OLE Objects With A Pop-Up Menu That Lists All OLE Verbs
Activating OLE Objects From Code
Is An Object Linked Or Embedded?
Handling Multiple OLE Objects
Using OLE Control Arrays To Handle Multiple OLE Objects
Loading New OLE Controls At Runtime
Dragging OLE Objects In A Form
Deleting OLE Objects
Copying And Pasting OLE Objects With The Clipboard
Zooming OLE Objects
Saving And Retrieving Embedded Object’s Data
Handling OLE Object Updated Events
Disabling In-Place Editing

In Depth
For obvious reasons, Object Linking and Embedding (OLE) is a very popular programming topic. Using OLE you can give the users of your program direct access to OLE server programs like Microsoft Word or Excel. In fact, you can integrate all kinds of programs together using OLE, giving your program the power of database, spreadsheet, word processor, and even graphics programs all wrapped into one.

Visual Basic lets you do this with the OLE control. This control can display OLE objects, and those objects appear as mini-versions of the programs connected to them. For example, if you display an Excel spreadsheet in an OLE control, the control displays what looks like a small version of Excel right there in your program. The program that creates the object displayed in the OLE control is an OLE server, and your program, which displays the OLE object, is called an OLE container. In fact, the proper name for the OLE control is the OLE container control.
You can use the OLE object in the OLE control just as you would in the program that created it; for example, you can work with an Excel spreadsheet in an OLE control just as if it was open in Excel itself. How does that work? There are two primary ways of working with the OLE objects in an OLE control: opening them and editing them in place.
When you open them, the OLE server application is launched in its own window and the OLE object appears in that application. When you want to save your changes to the OLE object in the OLE control, you use the server’s Update item in the File menu.
When you edit an OLE object in place, the server application is not launched in its own window; instead, the object becomes active in the OLE control itself and may be edited directly. The OLE container program’s menu system is taken over by the OLE server—and you may be startled to see Microsoft Word’s or Excel’s menu system in your program’s menu bar. To close an OLE object that is open for in-place editing, you click the form outside the object.
As an example, the Microsoft Excel spreadsheet in Figure 26.1 is open for in-place editing.

Figure 26.1  Opening an Excel spreadsheet in an OLE control for in-place editing.
When the OLE object in an OLE control is closed, it appears in its inactive state, as shown in Figure 26.2.


Figure 26.2  An inactive OLE object.
OLE actions are called verbs; for example, opening an OLE object is accomplished with the VbOLEOpen verb, and editing it in place is accomplished with the VbOLEInPlaceActivate verb. We’ll see how to handle OLE verbs in this chapter when we use the OLE control’s DoVerb method.
What other methods does the OLE control support? Those methods and what they do appear in Table 26.1. You can also use the OLE control’s Action method to invoke the methods in Table 26.1, and the values for this property also appear in Table 26.1. When you use the Action property, the control often uses other properties of the control, such as the SourceDoc property, to find the data it needs to perform the requested operation. Note, however, that the Action property is considered obsolete, and we’ll use the OLE methods instead.
Table 26.1 OLE methods.

Method
Action Value
Meaning

CreateEmbed
0
Creates embedded object

CreateLink
1
Creates linked object from the contents of a file

Copy
4
Copies the object to the system Clipboard

Paste
5
Copies data from the system Clipboard to an OLE container control

Update
6
Retrieves the current data from the application that supplied the object and displays that data as a picture in the OLE container control

DoVerb
7
Opens an object for an operation, such as editing

Close
9
Closes an object and terminates the connection to the application that provided the object

Delete
10
Deletes the specified object and frees the memory associated with it

SaveToFile
11
Saves an object to a data file

ReadFromFile
12
Loads an object that was saved to a data file

InsertObjDlg
14
Displays the Insert Object dialog box

PasteSpecialDlg
15
Displays the Paste Special dialog box

FetchVerbs
17
Updates the list of verbs an object supports

SaveToOle1File
18
Saves an object to the OLE version 1 file format

The term Object Linking and Embedding implies two ways of inserting objects into an OLE control—through linking and embedding such objects. How do those operations differ?
Linking Vs. Embedding
What’s the difference between linking and embedding OLE objects in the OLE control? The main difference has to do with where the object’s data (such as the data in a spreadsheet) is stored. Data associated with a linked object is manipulated by the OLE server application that created it and is stored outside an OLE container control. Data associated with an embedded object is contained in an OLE container control, and that data can be saved with your Visual Basic application.




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