There are several properties that are shared
by many of the standard controls.
Name
You use a control's Name property in code
to refer to the control object when you want
to manipulate its properties or methods. For
example, if you name a TextBox txtFirst, you
could write code to change its Enabled property
and invoke its Move method as follows:
txtFirst.Enabled = True
txtFirst.Move 100,200,500,200
A control's Name also becomes part of
all the event procedure names of that control.
See the section in this chapter on "Assigning
Code to a Control to Respond to an Event"
for more discussion and its implications.
You should always rename a control a meaningful
name as soon as you place it on its container.
Most VB programmers use the "Hungarian
notation" convention for naming controls
and variables. This means that the name of each
control begins with a lowercase prefix that
is one to three (or sometimes four or five)
letters long. The prefix is the same for all
objects of the same type.
For instance, you should rename a TextBox control
a name beginning with the letters txt as shown
in the example given just above with txtFirst.
Although you can reference the control's
Name property directly in code (though it's
almost never necessary), you cannot change the
Name property at runtime.
Enabled
The Enabled property of a control is a True/False
property that you can set to determine whether
or not the control can receive focus or respond
to user-generated events such as the Click event.
Many controls' Caption or Text properties
(including the CommandButton, TextBox and Label)
will appear fainter or "grayed out"
to the user when you set their Enabled properties
to False, as illustrated in Figure 3.12.
FIGURE 3.12 A form with Enabled and Disabled
controls.
Since the Label control never gets focus,
its Enabled property has no effect on whether
the user can set focus to the Label (the user
never could set focus to a Label, anyway). However,
an enabled Label can still receive events such
as the Click and DblClick events when the mouse
pointer is over it. Setting the Label's
Enabled property to False disables these events
for the Label as it does for other controls.
You can set a control's Enabled property
at both design time and runtime.
Visible
This property is True by default. Setting it
to False means that the control will not be
visible to the user. If you set Visible to False
at design time, you (the programmer) will still
be able to see the control on the design surface
but the user won't be able to see it at
runtime. You can set the Visible property at
both design time and runtime.
Font
This property is actually an object that contains
many properties of its own. You can manipulate
the Font object's properties through a
design time dialog box that you can call up
in one of two ways:
-
Double-click the word
"Font" in the control's
Properties window (see Figure 3.13).
FIGURE 3.13 The Font property dialog box.
-
Click the ellipsis button
(…) to the right of the word "Font"
in the Properties window.
You may also refer to the Font object's
sub-properties in your code by using double-dotted
syntax or the With construct. For instance,
if you wanted to make the type in the Label
named lblName appear bold (after first saving
its original Bold setting), you would write
the lines of code:
Dim blnOrigBold As Boolean
BlnOrigBold = lblName.Font.Bold
lblName.Font.Bold = True
However, if you wanted to refer to or manipulate
several Font properties at the same time, it
is more efficient to write lines such as
Dim blnOrigBold As Boolean, blnOrigUnderline
As Boolean
Dim sOrigFontName As String
Dim iOrigSize As Integer
With lblName.Font
BlnOrigBold = .Bold
.Bold = True
blnOrigUnderLine = .Underline
.Underline = False
sOrigFontName = .Name
.Font = "Courier"
iOrigSize = .Size
.Size = 24
End With
NOTE: Different Use of a Timer's Enabled Property
The Enabled property for the Timer control has a different meaning from the other
controls. When you set a Timer's Enabled property to True, you cause the Timer
event to fire at the interval of milliseconds specified by the Timer's Interval
property. When you set its Enabled property to False, the Timer event will not
fire.
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