A user uses an Active Document container application such as Internet Explorer
or Office Binder to directly open a second application's data file. The container application uses the
Windows Registry to determine the application associated with the data file's extension
and, if the data file's application is an Active Document server, it runs the server
application and its data in an Active Document window.
For instance, if an Internet
Explorer or Office Binder user attempts to open
a .DOC file, then IE or OB will host that file
in an Active Document implemented by Word. If,
on the other hand, the user opens an .XLS file,
then IE or OB will host that file in an Active
Document implemented by Excel.
You might now be wondering: What
data file must the user choose to bring up my
Active Document application written in VB? This
and other questions are answered in the following
sections.
Saving Information in the
.vbd File
The native document file format
for an Active Document application that you
create with VB is a file with a .vbd extension.
The .vbd file contains persistent property values
and other information that the container needs
to host your Active Document application. The
.vbd file is created at the same time the .EXE
file is compiled.
When the user tells the container
application to save information from your Active
Document (either because the user has chosen
a save option or because the user is trying
to exit your document), then the container application
saves the information back to the .vbd file.
When you run your VB Active Document
application from the VB design environment,
VB creates a temporary .vbd file in the VB program
directory. For more details on testing your
Active Document in the design environment, see
"Testing Your Active Document."
When you compile and distribute
your ActiveX DLL or EXE, the .vbd file is installed
in the same directory as the DLL or EXE.
Data Preservation Events
and the Properties Bag
As mentioned earlier in this chapter,
a UserDocument object
has the same ReadProperties
and WriteProperties
events as the UserControl
object of an ActiveX Control project.
Within the event procedures of
these events, you can use the Property Bag object's
ReadProperty and
WriteProperty methods to retrieve and
store persistent property values. Container
applications implement the Property Bag by reading
and writing the .vbd file. This happens transparently
to your Active Document application.
SAVING
INFORMATION WHEN A CONTAINER DOESN'T SUPPORT
THE PROPERTIES BAG
Although Internet Explorer and
Office Binder support the Properties Bag with
.vbd files, you can expect that other container
applications that appear in the future might
not use vbd files to implement a Properties
Bag.
In this case, you'll need
to change the type of code that you put in the
ReadProperties and
WriteProperties event procedures of the
UserDocument.
Instead of calls to the
ReadProperty method, you might put filehandling
code similar to the code in the listing below
into the ReadProperties
event procedure. It provides for a code
fragment to read data directly from a file into
a TextBox that delegates
an Active Document property.
Dim lHandle as Long
lHandle = FreeFile
Open lHandle for Input as _
gblstrPropBagFile
txtData.Text = _
Input(Lof(#lHandle), lHandle)
Close #lHandle
Instead of calls to the
WriteProperty method, you might put code
similar to the code in the listing shown below
into the WriteProperties
event procedure. It shows a code fragment
to write data directly to a file from a
TextBox that delegates an Active Document
property.
Dim lHandle as Long
lHandle = FreeFile
Open lHandle for Output as _
gblstrPropBagFile
Print #lHandle, txtData.Text
Close #lHandle
Note the use of the Open and Close statements and the Input function to manipulate
the file.
