Access 97/2000: Controls
What Are Controls?
As a program, Access is built to provide database
developers with a lot of flexibility. Part of this flexibility is having
different types of objects that carry out quite specific functions.
For instance, tables contain your structured data, queries allow you to
work with that data, forms present your data and help you to automate database
navigation and functions, and reports gather your data for printing.
All of the information stored in your tables and manipulated in your
queries is contained in fields. All of the information on a form
or report is contained in controls. Every item on a form or report
is, then, a control. Controls are articles on a form or report that display
data, perform actions, or enhance the object in question.
Types of Controls
Forms and Reports usually draw information from
Tables or Queries. Forms and Reports use graphical objects called controls
to link the object back to the underlying table or query. Three important
controls are text boxes
, frames
, and labels. Text boxes
display
names and numbers stored in your underlying table or query. Frames
show pictures and graphs. Labels display text as titles or other
markers that describe data, but are not linked to information in the underlying
table or query. Other kinds of controls, like lines and rectangles, visually
organize the information and group data on-screen. There are three types
of basic controls in Access: unbound, bound, and calculated.
-
Unbound: An unbound control allows you to display information that
is not stored in the database-- the title of the form or a descriptive
label. This kind of control does not have a data source. You use unbound
controls to enhance the presentation and clarity of your form by adding
titles or descriptive labels, lines, and pictures.
-
Bound:
A bound control is always linked to information stored in
the form's underlying table or query. A text box is always a bound control.
To display a person's name in a Mailing List
table, the text box
would get it from the Name field because you have bound it to that
field. You can also use a bound control to display a picture if it is stored
in the underlying table.
-
Calculated: Calculated controls are a subset of bound controls,
but they do not present information as it appears in a table or query.
Instead, they operate on data taken from the table or query by using an
expression - a combination of operators such as (+, -, and =), control
names, field names, and constant values. For example, the following expression
would combine a table's FirstName and LastName fields to
present them together:
=FirstName + ì î & LastName
Note:
Access's on-line help has more detailed information on building
expressions.
The Toolbox
The
Toolbox
is a special kind of toolbar containing buttons that allow you to select
the type of control that best suits your needs. Since the same toolbox
is used for designing both forms and reports, you may not find all tools
useful for all forms.
The toolbox should be visible when you enter the form's Design View
.
If it is not visible, you can turn it on by selecting Toolbox from
the View menu or by selecting the Toolbox icon on the toolbar.
The toolbox controls belong to five major categories: text display and
entry, presentation of yes/no options, list boxes, graphics and subforms,
and layout enhancement tools.
Text Boxes and Labels
Text boxes
and labels are the default tools for looking at information in an Access
form or report. Text boxes display the information entered in a field or
calculated on the form; labels are captions or descriptive text. You can
use labels to create titles and headings. All labels are unbound controls,
but they can be attached to other controls. Every text box you create
on your form will automatically have an attached label.
Yes/No Options
The toolbox
contains four different kinds of controls for displaying Yes/No values.
Check boxes
and optionbuttons
(also called radio buttons)
when turned on or selected indicate a Yes value. A check box
contains
a check mark when turned on, while an option button
has a dot when
selected. Toggle buttons
indicate a choice between two values. You
can change the face of a toggle button
to display your own text.
An
option group
shows which option was selected from several alternatives.
Option groups
frame a set of either check boxes
or option
buttons
.
Note: only one option in the field can be selected for each record.
Drop Down Boxes
Access's toolbox
contains two varieties of drop-down boxes: a List box and a Combo
box. These controls display a series of values from which you can select.
They are most useful when entering data. You can take the values for listing
in the boxes from existing values in a table or query or from a list you
specify using the control's properties. The most effective way to take
values from an existing table is to create a query that extracts all the
unique values from a table and sorts them.
Graphics Objects and Subforms
Forms can be
enhanced by including different kinds of graphics objects, or by including
other forms inside of the main form. The Graph tool allows you to
create a graph in Microsoft Graph
and place it on your form. The
Subform/Subreport tool lets you insert a pre-existing form into
your current form. The bound and unbound object frames allow you to insert
onto your form pictures or other OLE objects.
Layout Enhancement Features
You can improve
the appearance of your forms by including lines, boxes, or page breaks.
The line and box tools are designated sections of your form that you want
to separate visually from other sections. Page breaks allow you to control
how much information goes on one page of each form.
Selecting, Moving, and Sizing Controls
Access has easy drag and drop movement of controls
in forms and reports. You select a control by clicking on it. You can also
select several adjacent controls by "lassoing" them. To lasso, you need
to click in an open space on the form, then drag the pointer through all
of the controls that you want to select. Make sure that you start lassoing
from a point on the form that will allow you to drag through all of the
desired controls without intersecting any others. To select controls that
are not adjacent, you begin by clicking on the first control, then select
subsequent controls by clicking on them while holding down the <Shift>
key. Once selected, you can move a control and its attached label anywhere
in the form by dragging it to a new location.
If you place the cursor on a control's border, you will see one of three
options. An open hand means you can move both the control and its attached
label. A hand pointing with the index finger means that you can move either
the selected control or label, but not both. A double-headed arrow means
you can re-size the control. You then move or re-size by holding down the
left mouse button and dragging the control to its new location or size.
Customizing Your Controls
In Access, properties determine the characteristics
of fields, controls, tables, queries, forms, and reports. Every control
on a form has properties. Control properties determine the structure and
appearance of the control and the characteristics of the data it contains.
For instance, using a control's properties, you could set properties that
would format all displayed values as currency and in bold type. To modify
a control's properties by changing its property sheet, open the property
sheet by:
-
Double clicking on the control (unless you're using subforms/subreports
or unbound object frames).
-
Selecting the control by clicking on it. Now either choose Properties
from the View menu, or click the Properties button on the
toolbar.
-
Right-clicking on the control and selecting Properties from the
drop-down menu.
Where Control Properties Come From
A bound control in a form inherits the same property
settings that went with the field in the underlying table or query. These
settings include the Format,
InputMask, and DecimalPlaces
properties. If you set the input mask for a telephone number to be !(000)000-0000,
then your form would automatically include the parentheses and dash. If
you create a calculated control on the form, then it does not inherit any
properties from the underlying table or query.
Changing a Control's Properties
Changing a control's property setting does not affect
the property setting for the underlying field. You can set the appearance
to be different in a form, but creating a difference usually leads to a
cluttered look. Most of the time, for a uniform appearance, it is better
to set the Format,
InputMask, and DecimalPlaces properties
in the underlying table or query. The exception is calculated field properties,
which you will want to set to ensure the appearance of your data in the
form is as you desire.
You customize controls by changing their properties on the property
sheet. Access gives you several property categories. All Properties
shows
all of the control's properties. Data Properties
deal with the characteristics
of data displayed in the control, like the default data value, format,
or number of decimal places. Event Properties
specify a macro or
module to be executed when an event occurs such as pressing certain keys,
clicking or double-clicking the control, or changing data. Layout Properties
define
appearances like height, width, color, if the control can shrink and grow
with the data, and font characteristics. Other Properties
show the
control's name and the description that appears on the status bar. Note:
You
select a property by clicking on that option in the property sheet. If
you click on the property and an arrow appears, you can click the arrow
to display a list of settings. Otherwise, type an entry in the box.
Changing Properties for Multiple Controls
If you want several controls to have the same properties,
such as height, width, or color, you can save time by changing the controls
as a group rather than individually. To change the property of any control,
display the property of any control. Then, select the controls you want
to change by holding down the <SHIFT> key and clicking on each
one. Change the desired properties in the control sheet.
Changing an Object's Appearance
Once you have created a form or report, you need
to remember a few basics about working with controls in Access. First,
for the best way to create and position controls on your form, use both
the Toolbox and the Form Design Toolbar
. The Toolbox,
the Field List
for the underlying table or query, and the Properties
box can be displayed for easy access. You can turn all of these options
on by selecting the appropriate buttons from the Form Design
toolbar
or from the View menu.
The easiest way to create a new control is by selecting the type of
control you want in the Toolbox, and then clicking and dragging
in the form to create an unbound control. You can then bind the control
to a field in the underlying table or query by filling in the Control
Source
property with the appropriate field name. The best way to create
a new control is to combine these two actions into one. When the both the
Field List
and the Toolbox are displayed, you can select
the control type that you want to add in the Toolbox and drag the
field you want bound from the Field List
to the form's design window.
Aligning Controls
Access comes with tools that make it easy to get
all the controls to their desired location. To align controls use the Snap
To Grid
command in the Format menu. When this command is turned
on, Access automatically aligns controls to the grid. When you have selected
multiple controls, you can make the alignments match up. Under the Format
menu, select whether you want to align controls with each other or with
the grid underneath the form.
To Align One or More Controls to the Grid
-
Select the controls you want to align.
-
From the Format menu, choose Align, and then choose To
Grid
. Access will then align the upper left hand corner of each control
to the grid.
To Align Controls Relative to Each Other
-
Select the controls you want to align.
-
From the Format menu, choose Align, and then Left,
Right,
Top,
or Bottom depending on which edge you want to align. Left aligns
the edges of the controls with the edge of the leftmost control. Right,
Top, and Bottom do the same with the edge of the right, top, and bottom-most
control.
Note: When you are aligning controls relative to each other, select
only controls in the same row or column.
On-the-fly Control Switching
Older versions of Access had one huge annoyance
when it came to form design: you could not change one type of control into
another without deleting the control and replacing it with a different
type. The designers finally got around to remedying this problem in this
version. When you want to change a control's type on the fly, right-click
on the desired control and choose Change To
from the shortcut menu.
This allows you to ìmorphî a text box into a combo box.