Objects related to ActiveX control
The following are the objects that are
involved in the process of creating an ActiveX control.
¨
UserControl object
¨
AmbientProperties object
¨
Extender object
¨
Constituent control objects
UserControl Object
This is the object used to create a single
ActiveX control. Every ActiveX control is consisting of one UserControl object
and a set of constituent controls. Just like a From, a UserControl object also
has a designer, which allows you to place intrinsic control on the UserControl
object.
You have properties, methods, and events
for UserControl object. They are discussed later in this chapter.
AmbientProperties Object
This is used to get information from
container of ActiveX control. The
properties of AmbientProperties
object are the ambient properties of the control. These properties are read-only. These properties allow you to determine how
you adapt your control according to the capabilities of the container.
Not all ambient properties are standard.
Some of them are specific to only a particular container.
AmbientChanged event occurs whenever any of the ambient properties (properties in
container) changes. This enables programmer to change control according to the
container.
AmbientProperties object is not available in Initialize
event.
The following is the list of standard
ambient properties.
|
Property
|
Meaning
|
Default value if property is not supported by
Container.
|
|
BackColor
|
Color that
contains the suggested interior color of the contained control.
|
&H80000005
|
|
DisplayAsDefault
|
Returns True
if the control is the default control
otherwise false.
|
false
|
|
DisplayName
|
The name that
the control assigned by developer.
|
"".
|
|
Font
|
Contains the
suggested font information of the contained control.
|
MS Sans Serif 8.
|
|
ForeColor
|
Suggested
foreground color of the contained control.
|
0x80000008: the system color for window
text.
|
|
LocaleID
|
Specifies the
language and country of the user
|
System locale ID.
|
|
Palette
|
Picture
object whose palette specifies the suggested palette for the contained
control.
|
|
|
RightToLeft
|
Indicates the
text display direction and control visual appearance on a bi-directional
system.
|
False.
|
|
ScaleUnits
|
The name of
the coordinate units being used by the container.
|
""
|
|
TextAlign
|
Specifies how
text is to be aligned.
|
0 - General Align.
|
|
UserMode
|
Specifies if
the environment is in design mode or end user mode
|
True.
|
Table 28.1:
Ambient properties of a UserControl.
The following code changes the background
color of the text box to the background color of the container whenever
background color of the container is changed.
Private
Sub UserControl_AmbientChanged(PropertyName As String)
If
PropertyName = "BackColor" Then
txtNumber.BackColor = Ambient.BackColor
End If
End Sub
Listing
28.1: Changing BackColor property of text box to
BackColor property of user Control.
AmbientChanged event of the UserControl
object occurs whenever any of the ambient properties is changed. Ambient object
provides access to values of ambient properties.
PropertyName parameter of the AmbientChanged
event contains the name of the properties that has been changed in the
container.
Extender Object
This object holds properties of the control
that are actually controlled by the container of the control rather than by the
control itself
The properties, methods, and events of
Extender object are provided by the container. So there is no guarantee that
all these are supported in all platforms.
You can access extender properties using Extender property of UserControl.
The following is the list of extender
properties.
|
Property
|
Meaning
|
|
Name
|
Contains the
user-defined name of the control.
|
|
Visible
|
Specifies if
the control is visible or not.
|
|
Parent
|
Represents
the container of the control, such as a form in Visual Basic.
|
|
Cancel
|
Indicates
that the control is the Cancel button for the container.
|
|
Default
|
Indicates
that the control is the default button for the container.
|
|
Container
|
Represents
the visual container of the control.
|
|
DragIcon
|
Picture that
specifies the icon to use when the control is dragged.
|
|
DragMode
|
Specifies if
the control will automatically drag, or if the user of the control must call
the Drag method.
|
|
Enabled
|
Specifies if
the control is enabled. This is not present unless the control also has an
Enabled property.
|
|
Height
|
Specifies the
height of the control in the container’s scale units.
|
|
HelpContextID
|
Specifies the
context ID to use when F1 key is pressed being in the control.
|
|
Index
|
Specifies the
position in a control array that this instance of the control occupies.
|
|
Left
|
Specifies the
position of the left edge of the control to the left edge of the container,
specified in the container’s scale units.
|
|
TabIndex
|
Specifies the
position of the control in the tab order of the controls in the container.
|
|
TabStop
|
Specifies if
Tab will stop on the control.
|
|
Tag
|
Contains a
user-defined value.
|
|
ToolTipText
|
Contains the
text to be displayed when the cursor stays on the control for more than a
second.
|
|
Top
|
Specifies the
position of the top edge of the control to the top edge of the container,
specified in the container’s scale units.
|
|
WhatThisHelpID
|
Specifies the
context ID to use when the What’s This
pop-up is used on the control.
|
|
Width
|
Specifies the
width of the control in the container’s scale units.
|
Table
28.2: Extender properties.
The following are the methods provided by Extender object.
¨
Drag
¨
Move
¨
SetFocus
¨
ShowWhatsThis
¨
Zorder
The following are the events provided by Extender object
¨
DragOver
¨
DragDrop
¨
GotFocus
¨
LostFocus
Properties of UserControl object
The following are the properties that are
specific to user control object.
|
Property
|
Meaning
|
|
AccessKey
|
Returns or
sets a string that contains the keys that will act as the access keys (or hot
keys) for the control.
|
|
Ambient
|
Returns an AmbientProperties object holding the
ambient properties of the container.
|
|
ContainedControls
|
Returns a
collection of the controls that were added to the control.
|
|
EditAtDesignTime
|
Returns or
sets a value determining if a control can become active during the developer
design time
|
|
EventsFrozen
|
If it is set
to true, then events of usercontrol are ignored by container
|
|
Extender
|
Returns the Extender object for this control that
holds the properties of the control that are kept track of by the container.
|
|
ParentControls
|
Returns a
collection containing other controls in parent container.
|
|
PropertyPages
|
Is a string
array containing the names of the property pages in the project that are
associated with this control.
|
|
ContainerHwnd
|
Returns the
window handle (hWnd) of a UserControl’s container.
|
|
Parent
|
Returns a
reference to the container object on which the control is sited.
|
|
CanGetFocus
|
Determines
whether focus should move to this control or not.
|
Table
28.3: Properties of User Control.
UserControl Events
The following are the various events of
usercontrol object and their description.
|
Event
|
When does it occur?
|
|
AccessKeyPress
|
Occurs when
user presses one of the accesskeys for the control. It passes the key that is
pressed by user.
|
|
AmbientChanged
|
Occurs when an ambient property’s value changes. This passes the
name of the property as the only parameter
|
|
EnterFocus
|
This event
occurs whenever a constituent control receives focus.
|
|
ExitFocus
|
Occurs
whenever focus leaves the control.
|
|
GotFocus
|
Occurs in the
constituent control when focus enters it. The EnterFocus event is raised before the GotFocus event.
|
|
Hide
|
Occurs when
the object’s Visible property
changes to False.
|
|
InitProperties
|
Occurs when a
new instance of an object is created.
This allows
programmer to initialize new control when it is placed on the form.
|
|
ReadProperties
|
Occurs when
loading an old instance of an object that has a saved state. This is used to
read the values of the properties. Used for property persistence.
|
|
Show
|
Occurs when
the object’s Visible property
changes
|
|
WriteProperties
|
Occurs when
an instance of an object is to be saved.
This is used to save the values of properties.
|
|
AsyncReadProgress
|
Occurs when
more data is available as a result of an AsyncRead
method.
|
|
AsyncReadComplete
|
Occurs when
the container has completed an asynchronous read request.
|
|
HitTest
|
Occurs when
the user moves the mouse over a UserControl object. Only occurs when the Windowless property of the
UserControl is set to True and the BackStyle
property is set to Transparent.
|
|
Initialize
|
Occurs when
an application creates an instance of a user control.
|
|
Terminate
|
Occurs when
the instance of the control is about to be destroyed.
|
Table
28.4: Events of user control object.
Property Pages
Before we started creating ActiveX Control,
we had already used a few ActiveX controls.
All of them have Property pages that allow you to change properties of
the control. Now let us create two
property pages for our Number control. First one contains a text box to take
number from user and changes Value
property, Second one contains two text boxes Maximum Length and Minimum Length
properties. A developer using Number
ActiveX Control can invoke property pages and change properties.
The best way of creating a property page is
using Property Page Wizard. Now
having decided how many property pages to have and what to have in each of
these property pages, we are ready to use Property Page Wizard.
To
invoke property page wizard:
1.
First make Property Page Wizard
available to Visual Basic project by selecting
Add-Ins menu and then select Add-In Manager option.
2.
In Add-In Manager dialog box double click on VB 6 Property Page Wizard. You should see Loaded message in Load
Behavior column.
3.
Click on Ok.
4.
Then select Add-Ins menu and Property Page Wizard. You will see a series of windows prompting
for required information.
The following are the steps to create two
property pages and to place Value
property in first property page and MinLength
and MaxLength properties on the
second property page.
1.
When Property Page Wizard is
displayed, it first displays Introduction screen.
2.
Click on Next button to move to select the Property Pages page.
3.
Click on Add button.
4.
Enter ppValue
as the name of the page.
5.
Click on Add button again and
enter ppLength as the name of second
property page.
6.
Click on Next
button to move to Add Properties page.
7.
Available Properties list
contains the list of available properties.
8.
Make sure ppValue tab is selected in Available Property Pages.
9.
Select Value property and click on > to move the property to ppValue property.
10.
In the same way select ppLength tab and click on >> to place MinLength
and MaxLength properties on ppLength property page.
11.
Click on Finish button to start building property pages.
12.
Invoke ppValue property page and change Caption property to “Value”
13.
Invoke ppLength property page and change Caption property to “Length”.
Property Page Wizard has created two
property pages ( ppValue and ppLength, shown in figure 28.3, and 28.4).
The code that Property Page Wizard has
written for ppValue property page is
as follows.
Private
Sub txtValue_Change()
Changed = True
End Sub
Private
Sub PropertyPage_ApplyChanges()
SelectedControls(0).Value = txtValue.Text
End Sub
Private
Sub PropertyPage_SelectionChanged()
txtValue.Text = SelectedControls(0).Value
End Sub
Listing 28.1: Code
written by property page wizard.
Let us understand the code written by
Property Page Wizard. But before we try to do that, we have to understand
properties, events of property page.
Changed Property
When this property is set to true, Apply
button in the property page will be enabled.
In addition to that, setting it to true calls ApplyChanges event whenever you click on Ok button or move to a different property page.
SelectedControls property
This is a collection that contains the
controls that are currently selected on the form. SelectedControls (0)
references the control that is currently selected. This is used to get the
values for properties of the currently selected instance of the ActiveX control
for which property page belongs.
The code written by Property Page Wizard,
uses SelectedControls (0) (first
selected control) only. If you want to handle all selected controls, you have
to modify the code written by wizard.
SelectionChanged Event
This is fired whenever an instance of the
ActiveX control is selected for editing properties through property pages. This event is used to get the values of the
properties from selected control (SelectedControls
(0)) and assign those values to controls in property pages to enable user
to change them.
ApplyChanges Event
This event is fired whenever user is
selecting Apply button, selecting Ok button, closing page or shifting to
a different page.
The event occurs only when Changed property is set to true,
Now, if you look at the code written by
Property Page Wizard, you should be able to understand the code. The code uses
all the properties and events that we have discussed. The following is the
summary of the code.
¨
Sets Changed property to True, whenever user changes values in txtValue text box, which is meant for Value property.
¨
SelectionChanged event is used to get
the value of Value property of the
currently selected control (SelectedControls(0))
and put that value in txtValue
textbox.
¨
ApplyChanges event is used to write
value entered in txtValue textbox
into Value property of the currently
selected control (SelectedControls (0)).
Code for ppLength property page
The code written by Property Page Wizard
for ppLength property page is as follows.
Private
Sub txtMaxLength_Change()
Changed = True
End Sub
Private
Sub txtMinLength_Change()
Changed = True
End Sub
Private
Sub PropertyPage_ApplyChanges()
SelectedControls(0).MaxLength = txtMaxLength.Text
SelectedControls(0).MinLength = txtMinLength.Text
End Sub
Private
Sub PropertyPage_SelectionChanged()
txtMaxLength.Text = SelectedControls(0).MaxLength
txtMinLength.Text = SelectedControls(0).MinLength
End Sub
Listing
28.2: Code for ppLength property page.
This code needs no explanation, as it
doesn’t differ from the previous code.
Using property pages at the time of designing
Let us see how a developer who is using
Number ActiveX control can use Property Pages of Number control. Here are the steps to test it:
1.
Open testing project
(tstNumctrl) project
2.
Invoke Form designer
3.
Select Number1 control and
click right button
4.
You should see a new option in
popup menu – Properties.
5.
Select Properties option to invoke Property pages.
6.
Property pages window is
displayed with two tabs at the top, one for Value property page and another for Length property page.
7.
In Value property page, you will see the value you assigned to Value property of the selected control.
As shown in figure 28.5 , the value assigned to Value property is 1000. So
initially you will see 1000.
8.
Change the value to 2000 in
property page. It will enable Apply
button of the property page. At this
stage, your property Page should be identical to figure 28.5.
9.
Click on Apply to make Value
property of Number1 control. Click on Length
tab to move to Length property page.
Note: Pressing F4 on the control will invoke Properties Pallette. And
selecting Popup Menu -> Properties option will invoke Property
pages. This is same for all ActiveX controls.
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