Many Active Document projects will have more than one type of Active Document.
In these cases, you will have two or more
UserDocument objects, and it may be necessary
to pass data between the two documents. This can occur when one document has data upon which
the other document depends.
Additionally, with Active Documents, you do not necessarily know in what sequence
your Active Document was invoked. You might expect that the normal course of your application
is to use document A, for example, and then document B. However there is no automatic way
to prevent the user from going to document B directly. If you have code in document B that
depends on data from document A, you could have some problems.
This behavior can be controlled using global variables to pass between documents.
Consider a VB project made up of three files: a Standard Code module and two
UserDocument modules. In the Code module, a global variable called
gobjCurrentDocument is defined as an object. This variable is used to pass the document
object references between documents. The entire contents of the Standard module reads as follows:
Option Explicit
Public gobjCurrentDocument As Object
The two UserDocuments are for the most part identical; they
both display each other's data. The code listing for one UserDocument
is shown as follows (the code listing for the second UserDocument
would simply contain changed references to the "other"
UserDocument):
Public Property Get DocText()
'Return the current document's code
DocText = txtMyDoc.Text
End Property
Private Sub Command1_Click()
'Navigate to a new document
Set gobjCurrentDocument =
Me
Hyperlink.NavigateTo App.Path & "\usrdoc2.vbd"
End Sub
Private Sub txtMyDoc_Change()
PropertyChanged "DocText"
End Sub
Private Sub UserDocument_ReadProperties(PropBag As PropertyBag)
txtMyDoc.Text = PropBag.ReadProperty("DocText",
"")
End Sub
Private Sub UserDocument_Show()
'When show is called
then get the other documents
'data using the global
variable
If gobjCurrentDocument Is
Nothing Then
txtOutPutFromOtherDoc.Text
= "No Older Document"
Else
txtOutPutFromOtherDoc.Text
=
gobjCurrentDocument.DocText
'destroy
the object reference
Set gobjCurrentDocument
= Nothing
End If
End Sub
Private Sub UserDocument_WriteProperties(PropBag
As PropertyBag)
PropBag.WriteProperty "DocText",
txtMyDoc.Text, ""
End Sub
Each module has only the following procedures:
-
The DocText property is used to return the document's data.
-
The Command1_Click event sets the global variable to
the current document and then navigates to the other document.
-
The Show event is fired when the document is displayed.
The global variable is checked, and the data from the other document is shown on
a No Older Document message.
-
The Change event of the TextBox calls
the PropertyChanged method to alert the system that the
DocText property has changed.
-
If there has been a change in the DocText property, the
WriteProperties event fires when the container closes the document.
-
The ReadProperties event fires each time the document
is resited in its container.
When the application is executed in an Internet Explorer container, a window appears, as shown in Figure 14.5.
FIGURE 14.5 The first document opened.
Notice that the Document Two text box is set to No Older Document.
This means that the global variable is set to Nothing, indicating that an older instance of
Document Two has not yet run during this session. When the user presses the
CommandButton, a window appears, as shown in Figure 14.6.
FIGURE 14.6 The second document opened.
Notice that the second text box now has Document One's data. You could further
enhance this method to enforce the sequence in your Active Documents. If the global
variable were not equal to a predetermined value, you could then notify the user
and navigate to the appropriate document.
