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Fig 5.1B Addressing the objects

frmFindStay

txtName

subStayList

+ fsubStayList

current record

Ctrl+G: Open the

Immediate window

we look for the SourceObject property of subStayList.

The result is the name of the fsub. (Notice that our pre-

fix rules help us distinguish between the subform con-

trol and the fsub connected to this control).

19. Try setting SourceObject to nothing (an empty text

in quotes):

Forms!frmFindStay!subStayList. SourceObject = ""

The subform in the user window becomes blank.

Try setting it back again (it is a text, so remember

the quotes.)

As soon as we set SourceObject, Access closes the

previous subform and opens the new one. The Source-

Object property is a dialogue variable, so a change will

not survive close and open.

Form property. Above we looked at the SourceObject

property, which is a text - the name of the fsub. But a

subform has another interesting property, Form. It is a

reference to the open form that is shown in the subform

area. You cannot see this property in the property box

because it is not a text, but a pointer that only exists in

user mode. However, you can use the Form property in

VBA.

20. Try this command in the Immediate window:

?Forms!frmFindStay!subStayList. Form!name

It should print the name of the guest selected in the

subform area. The first part is the reference to sub-

StayList on frmFindStay. Now comes a dot saying that

we look for the Form property of subStayList. The re-

sult is a reference to the open form that is shown in the

subform area.

Next comes a bang and a reference to the name field,

i.e. the address of a guest. Now which guest? The sub-

form shows many records - which of the addresses will

we get? The address in the currently selected record.

Was this what you got? Try selecting another record on

the list and repeat the command.

Bang versus dot

21. Try using a dot instead of a bang before name:

?Forms!frmFindStay!subStayList. Form. name

It doesn't print the name of the guest, but the name of

the subform. Because of the dot, the statement asks for

the name property of the form.

When you use the bang, you ask for a control on the

fsub - or a field in the bound record behind the fsub.

Abbreviations. Above we have used the full address

expressions, but Access allows various abbreviations.

For instance you may refer to the guest control of the

subform in any of these ways:

Dot instead of bang

Forms!frmFindStay!subStayList. Form. address1

This works only because there is no address1 property

in a form.

Form omitted

Forms!frmFindStay!subStayList!guest

However, you cannot omit Form and use a dot at the

same time. Access will believe that you ask for a prop-

erty of the sub-control.

Warning. The bang mechanism works only in Visual

Basic. It doesn't work in SQL. For instance you have to

write

... JOIN ON tblGuest.guestID = tblStay.guestID

If you write

tblGuest!guestID

, the system gives an error

message.

5. Access through Visual Basic

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5.2 Event procedures (for text box)

Above, we have executed VBA statements through the

Immediate window, but when the user uses the system,

we need another way to activate VBA. We want the

system to respond to user actions, for instance the user

clicking a button, typing something in a text box, etc.

These user actions are called events. You can write a

VBA procedure for each kind of event.

AfterUpdate event

We will now write an event procedure that makes

txtName respond when the user has entered a search

criterion.

1. Open frmFindStay, select the txtName search cri-

terion, and view the property box. (In Access 97

you can only do this in Design mode.)

2. Look at the Event tab. It has a list of the events

that the control can respond to (Figure 5.2A). The

event we are interested in is AfterUpdate. It hap-

pens when the user has finished entering the text in

the control.

3. Create event procedure. Choose AfterUpdate, the

three dots, and Code Builder. This creates the

event procedure for AfterUpdate.

You are now in the Visual Basic window. You may

make the window smaller so that you can see frmFind-

Stay too. Also make the Access window smaller so that

you can see the two windows side by side.

Inside the Visual Basic window you see the event pro-

cedure for AfterUpdate (Figure 5.2A, right). The first

line reads

Private Sub

txtName_AfterUpdate

It shows that it is the AfterUpdate subroutine (proce-

dure) for the txtName control.

4. The body of the procedure is initially empty. Now

enter this statement:

Me!subStayList . Requery

Me. The word Me means the open form where this

control is placed - in this case the same as

Forms!frmFindStay

. We ask Access to find the

subStayList control. Finally we ask Access to call the

procedure Requery in this control. The result is that

subStayList recomputes the query behind the subform.

Since the query gets its where-condition from txtName,

the stay list should change.

Omitting Me. In most cases you can omit Me. You

may for instance write

subStayList . Requery

The exception is when some built-in function or

property has the same name as the control. In the

following sections we will sometimes write Me for

emphasis, sometimes omit it.

When is the AfterUpdate procedure called? Whenever

the user shows that he has finished entering the text, for

instance when he clicks on another control in the same

form, tabs to another field, or hits Enter. Try it:

5. Enter a criterion in the name field, for instance "a".

Click Enter. The stay list should now shrink ac-

cording to the new criterion. Enter another crite-

rion and use Tab. The system should respond.

6. Change the criterion and then - without using En-

ter, etc. - click in another window, for instance the

property box. The stay list should not change be-

cause txtName still has the focus and Access as-

sumes that the user hasn't finished the field. Now

click another field on FindStay. The stay list

should respond.

5.2.1 More text box properties

We will now make txtName respond each time the user

hits a key. To do this, we need to act on another event,

OnChange. This event happens whenever the user

types something in the text box or deletes a character.

When Access calls this event procedure, the situation is

a bit complex because several properties of the text box

are involved:

Value: This property is the value before the user

started editing the text box. Note that Value is the

default property for a text box, so if you don't spec-

ify another property in your address expression,

VBA will use Value. When the Value property is

empty, it has the value Null, similar to a database

field

Text: The value the user enters, but hasn't finished yet.

This is the text the user sees on the screen, but it is

not yet stored in Value. You can only access this

property when the text box has the focus. At other

times, the Text variable doesn't exist at all. When

the Text property is empty, it is a zero-length text

with the value "", similar to a VBA string variable.

OldValue: The value before the user started editing the

text. For bound controls (bound to a field in the

database), this is the same as the value in the

database. When the entire record is complete,

Access transfers Value to OldValue. OldValue is

useful when the editing must be undone for some

reason. For unbound controls, OldValue and Value

are always the same.

5. Access through Visual Basic

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Fig

2A An event procedure

Click three dots.

Select Code Builder

Form

module

Important Textbox attributes

Value:

Last value completed by user (default attribute)

Text:

What user sees during editing

OldValue:Value saved in database

Change event

We will now make txtName respond to each keystroke.

Proceed in this way:

7. On the event tab for txtName, choose OnChange

and the three dots. You now see the event proce-

dure for the Change-event.

8. Write these statements in the procedure body (Fig-

ure 5.2A):

Me.txtName = Me.txtName.Text

Me.subStayList.Requery

Me.txtName.SelStart = 100

9. Try it in user mode. As soon as you enter some-

thing in the text box, the stay list changes accord-

ingly.

The first procedure line copies Text to the Value of the

control. As a result, Value becomes what the user has

entered until now. Then the program recomputes the

stay list. During this it gets the search criterion from

the value of txtName. This is why we moved Text to

Value.

The last procedure line is more of a mystery. If you try

using the system without this line, the entire text box

becomes selected whenever you enter something. This

seems to be an undocumented side-effect of setting the

Value. To compensate for it, we let the program define

what is selected. We define the selection start point

(SelStart) to be character 100 of the text. Since the text

is much shorter, Access interprets it as being the end of

the text.

This solution works, but not very well. If you for in-

stance try to change a few characters in the middle of

the search criterion, the system annoyingly moves the

cursor to the end of the text. We could repair it by

storing the position before we set the Value, and set it

back afterwards. This is messy, and in the next section

we will show a more professional solution.

5. Access through Visual Basic

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5.2.2 Computed SQL and live search

We will now the professional solution. We don't

change Value at all, but compute the SQL-statement to

be used for the stay list. Let us first assume that the

user has entered the search criterion john. The event

procedure could then compute the list of stays in this

way:

Me.subStayList.Form . RecordSource = _

"select * from qryStayList where name like ( '*john*' );"

This is one long Visual Basic statement split into two

lines by means of the space and underscore at the end

of the first line.

Now, what does the statement do? The first line refers

to the open form in subStayList. The form has a record

source property, which defines the records to display.

We had bound the form to qryStayList, so the record

source was "qryStayList".

Now the procedure changes the record source to the

SQL statement in the second line. This statement takes

all records in qryStayList where the name contains

john. And it selects all attributes from the records. This

is what we need.

Notice that the SQL statement is a text surrounded by

double quotes. Inside the statement we have another

text string '*john*'. This text string is surrounded by

single quotes to distinguish it from the large text. We

haven't cared to write SELECT etc. with caps. The

SQL engine accepts the statement anyway.

The only problem is that john should be the text that

the user has entered. So the event procedure has to

compose the SQL statement from three parts, like this:

"select * from qryStayList where name like ('*" & _

Me.txtName.Text & "*');"

Note: Some developers don't use single quotes for the

text inside the text. They use double quotes for the

inner text. So instead of

" . . . like ('*" &

they would write

" . . . like (""*" &

The rule is that inside a text string, the characters ""

mean a single ".

Try it out

You may try the solution right away, but take care. The

next time you open frmFindStay and try to search,

Access remembers the SQL statement your program

has set. It uses this statement as the initial query for the

future. (I would call this an error.)

To avoid problems do as follows:

1. In qryStayList, remove the user criterion that we

defined earlier (like . . . ). We don't need it any-

more.

2. In fsubStayList, the record source is qryStayList.

Change it to select * from qryStayList;

3. Change the event procedure and try it out (see

Figure 5.2B).

You should now have a live search similar to the one

used in the real system.

(If Access still remembers the previous search crite-

rion, open frmFindStay in design mode and set once

more the Source Object of subStayList to fsubStayList.)

Computed SQL may seem very cumbersome. Yes - it

is, no doubt! However, when we need complex user

criteria, for instance a combination of name and/or

phone and/or date, the easiest way is to let the program

compute the SQL statement. In general, computed SQL

is the professional way to make complex systems.

In the next section we will use computed SQL to deal

with combinations of search criteria, some of them live

and some lazy.

5. Access through Visual Basic

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Fig 5.2B Computed SQL and live search

Define new

record source

To make it work properly:

Remove the old user criterion from qryStayList.

Set record source of fsubStayListto: select * from qryStayList;

Change the event procedure as above. Try it out.

Compute SQL from

part1 & part2 & part3

Note the single quotes around

text strings that end up in SQL:

(

'*"

& . . . &

"*'

); "

5. Access through Visual Basic

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5.2.3 Composite search criteria

Figure 5.2C shows an example where the user can use

one or more criteria in any combination - composite

search criteria. The figure also shows the programmer

names of the various controls. The name criterion is

called txtName, the booked criterion chkBooked, etc.

The user may fill in part of the guest's name, and/or

parts of his address, etc. The user may also restrict the

search to booked stays, and/or checked-in stays, etc.

To achieve this, the program must generate a suitable

SQL statement for each combination of criteria. The

pattern in the final SQL should be this, with optional

parts shown in square brackets:

SELECT * FROM ... WHERE TRUE

[ AND name Like( "*john*") ]

[ AND address1 Like( "*buf*") ]

[ AND phone Like( "*3700*") ]

[ AND arrival = #21-10-02# ]

AND (FALSE [ OR state=1 ] [OR state=2 ]

[ OR state>2 OR ISNULL(state) ] );

Notice that we start with a useless TRUE before the

optional AND's, and a useless FALSE before the

optional OR's. This is a trick that makes the program

far simpler. Each piece of the program doesn't have to

care whether it adds the first element to an AND/OR

list, or a later element.

The figure shows the program that generates the SQL

statement. It gradually builds up the SQL-statement in

the string variable s. First it puts SELECT * . . . TRUE

into s. Next it tests whether the name criteria holds

something. If so, it appends AND name Like . . . to s.

And so on. Finally, it stores the SQL statement as the

records source of the stay list.

In the places where the pattern has john, buf, etc., the

program inserts the value from the appropriate text

box.

Notice how we have written SQL parts in caps.

Professionals do so to make the SQL pattern stand out

more clearly. We explain the details below.

Shared procedure

When should this tricky piece of program be executed?

If the screen used an ordinary Search button, the

program should be the event procedure for the button.

However, we want to make a live search. In this case

the program must be executed whenever one of the

criteria changes value, i.e. for a whole bunch of event

procedures.

The solution is to make the program piece a separate

procedure. It starts with Private Sub and ends with End

Sub (see more on procedures in section 6.2). The

appropriate event procedures call this procedure as

shown for txtName_Change, txtArrival_AfterUpdate

and chkBooked_AfterUpdate.

Live search criteria

In order to make a live search, the program must

respond whenever the user has typed something. The

partially finished criteria are used for the search, and

the stay list shrinks gradually. While the user types, the

result is not in the box's Value, but in the temporary

variable Text. The other text box values are in Value.

It would complicate the search procedure to deal with

this too. The solution is to let the event procedures

store the current criteria in the variables copyName,

copyStreet and copyPhone. The event procedure

txtName_Change shows how. The search procedure

uses these copies to generate the SQL statement.

Note how we have declared the copy variables in the

first line of the form (see more in section 6.2).

Lazy search criteria

Some of the search criteria should not be live. The

check boxes, for instance, are either true or false. It is

sufficient to let their AfterUpdate procedure call the

search procedure and let it use the checkbox values. No

copy is needed.

The arrival date might be live, but while the user types

the date, the intermediate value has little meaning. The

stay list would just flicker and confuse the user. For

this reason, the arrival date reacts only at AfterUpdate.

Date comparison

In Figure 5.2C, the arrival date is a text box control

with the format property short date. Access will check

that the text corresponds to a valid date. It will show

the date according to the format property, but it will

store it as a Double number - the number of days since

the end of 1899 (see page 11).

When generating the SQL statement, the program uses

the CDbl function (Convert to Double) to show the

date as a number:

" AND arrival = " & CDbl(txtArrival)

This would generate an SQL fragment like this:

AND arrival = 37550

Later, the SQL engine will compare the dates in their

number form, and everything works fine.

Why all this fuzz? Couldn't we simply write:

" AND arrival = " & txtArrival

When Access appends txtArrival, it converts it to text

format by means of the CStr function. This function

produces a date in the regional date format set up in

MS Windows. With a European date format, we would

get this SQL fragment:

AND arrival = 21-10-07

SQL would reject it since dates have to be enclosed by

# #. So what about this:

" AND arrival = #" & txtArrival & "#"

5. Access through Visual Basic

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Fig 5.2C Composite criteria

txtName

Dim copyName As String, copyStreet As String, copyPhone As String

Private Sub search()

Dim s As String

s = "SELECT * FROM qryStayList WHERE TRUE "

If copyName <> "" Then s = s & "AND name Like( '*" & copyName & "*' ) "

If copyStreet <> "" Then s = s & "AND address1 Like( '*" & copyStreet & "*' ) "

If copyPhone <> "" Then s = s & "AND phone Like( '*" & copyPhone & "*' ) "

if txtArrival > 0 Then s = s & "AND arrival = " & CDbl(txtArrival)

s = s & "AND (FALSE "

If chkBooked Then s = s & " OR state = 1 "

If chkCheckedIn Then s = s & " OR state = 2 "

If chkOther Then s = s & " OR state > 2 OR ISNULL(state) "

s = s & ");"

Me.subStayList.Form.RecordSource = s

End Sub

Private Sub txtName_Change()

copyName = txtName.Text

Call search

End Sub

Private Sub txtArrival_AfterUpdate()

Call search

End Sub

Private Sub chkBooked_AfterUpdate()

Call search

End Sub

frmFindStay3

txtStreet

txtPhone

chkBooked

chkCheckedIn

chkOther

Sub search doesn't know whether criteria

are in Value or Text. So they are always here.

SELECT * FROM qryStayList WHERE

TRUE AND name Like('*joh*') . . .

AND (FALSE OR state = 1 . . .

. . . );

txtArrival

Now we would get this fragment:

" AND arrival = #21-10-07#

Looks all right, but unfortunately, SQL expects dates in

the US format. In this case it would reject 21 as a non-

existing month, in other cases produce a wrong result.

Fortunately, the Access database engine can treat dates

as double numbers, but other databases may not. In

such cases you would have to generate the dates with

an explicit US-format, for instance in this way:

" AND arrival = #" & Format(txtArrival, "mm/dd/yyyy") & "#"

Empty texts

An empty field in the database has the value Null for

all types of fields. The same applies for the Value in an

empty text box. To test for an empty field , we would

ask for IsNull(f). In a VBA string variable, an empty

text is a zero-length text with the value "". Since

copyName is a string variable, we ask whether the text

is different from "".

Null values

Notice how the program deals with Other stays, i.e.

stays that are neither booked nor checked-in. These

stays include those with state > 2 and those without a

state (a NULL state). Stays with a NULL state are not

real stays, but records generated by the outer join for

guests that don't have a stay.

Initialize the form

A final touch is to make the Find Guest screen

initialize itself properly:

•

Let the three checkboxes have a mark initially.

Otherwise, the stay list will be empty initially and

the user may panic. To do this, set the initial value

of the boxes through their property sheet.

•

Let the Form's Load event procedure call the

search procedure in order to make the stay list

match the initial criteria:

Private Sub Form_Load()

Call search

End Sub

Try it out

You should try to make the solution work in practice. It

is a challenge, but fun. Make a copy of frmFindStay

and use it for the experiment.

5. Access through Visual Basic

5.2.4 Event sequence for text box

We have now looked at two events for the text box,

Change and AfterUpdate. However, there are many

more, as you can tell from the Event tab in the property

box. (Select the event procedure and click F1 to get an

explanation of the event.) Figure 5.2D shows typical

event sequences for a text box. We will explain what

happens.

User clicks in the text box. First, the text box's Form

object may get a Current event. This happens if the

text box is in a record that wasn't selected before.

Next, the text box receives two events, Enter and

GotFocus. Enter signals that now the control is

active. Before calling the Enter event-procedure,

Access creates the Text property and sets it to the

current Value of the text box. GotFocus signals that

typing will now go to this control.

Then the textbox receives this series of events:

MouseDown, MouseUp, Click and maybe also a

DblClick.

User types an Ascii character. The text box receives

four events: KeyDown, KeyPress, Change, KeyUp

(plus mouse events if the mouse is used). KeyDown

occurs when the user depresses any key. The event

procedure has parameters that give details of the

physical key and other keys depressed at the same

time, for instance Shift and Ctrl. KeyPress occurs

when the key has generated an Ascii character, for

instance a letter, digit, space, tab or backspace. All

of these correspond to characters in the Ascii al-

phabet.

The Change event occurs when the visible content

of the control has changed, for instance that a char-

acter was added to the text or a character was de-

leted. Before calling this event procedure, Access

updates the Text property so that it contains what

the user sees.

The KeyUp event occurs when the user releases the

key. If the user keeps the key down to generate for

instance a whole sequence of x's, each x generates

KeyDown, KeyPress and Change. The KeyUp oc-

curs only when the user releases the key.

User types a non-Ascii character, for instance Arrow

left or F6. This generates only the KeyDown-event

(and the KeyUp). Nothing happens to Text or

Value, and no Change event is generated.

User types Delete. Delete is not an Ascii character, so

no KeyPress-event occurs. However, one or more

characters may be deleted, and then a Change event

occurs. KeyDown and KeyUp occur too.

User tabs to the next field. Access generates several

events. KeyDown occurs since the user pressed the

Tab key. BeforeUpdate shows that the user has fin-

ished the field, but it is not yet accepted. Before

calling the event procedure, Access has copied Text

to Value. BeforeUpdate may check the value, and

in case something is wrong reject the update.

Rejecting the update means that focus remains on

the text box and no AfterUpdate event is generated

yet. The user may edit the field or click Esc to set

the value back to its old value.

If it is an unbound control (not connected to a

database record), Access will also copy Text to

OldValue before calling the procedure. This is quite

illogical because OldValue is intended for letting

the program restore an erroneous field. This is not

possible for unbound controls.

Next comes the AfterUpdate-event. The value has

been checked and the procedure may act on it. In

the example above we used this opportunity to re-

compute the stay list. If it is a bound control, the

value will not yet be stored in the database, nor will

OldValue be changed. Storing the value in the

database doesn't happen until the user moves to

another record or explicitly saves the record with

Shift+Enter (or Records -> Save Record).

Next comes the Exit event. It signals that the field is

not active anymore. Finally, LostFocus occurs and

signals that typing will go to another control. When

both events have occurred, the Text property disap-

pears.

What about KeyUp? It happens in the next field,

which accordingly receives the KeyUp event.

Before that, the next field receives Enter and

GotFocus - in the same way as if the user clicked in

the next field.

What about errors in what the user has typed, for

instance an incorrect date? Access shows an error

message to the user instead of calling Before-

Update, and the cursor remains in the field. Can't

the program interfere before this error message?

Yes it can. The form receives a Form_Error event,

which may take action and cancel the error message

that Access was about to show (see section 5.5.10).

User clicks in next field. Access does almost the same

as when the user tabs to the next field. The only dif-

ference is that there is no KeyDown event.

User moves to next record. First the text box in focus

will receive the same events as if the user moved to

another control in the same record.

Next, the Form object receives three events.

BeforeUpdate signals that the record is about to be

saved and that the program may check that values

are correct and consistent with each other. The Be-

5. Access through Visual Basic

Fig 5.2D Event sequence, textbox

User action

Events

Property changes before call

Click in textbox

(Form: Current)

Enter.

Text = Value, OldValue = Value

GotFocus.

MouseDown, MouseUp

Click, (DblClick).

Type Ascii character KeyDown, KeyPress.

(letter,digit, tab . . . ) Change.

Text = Modified text

KeyUp.

Type ArrowLeft or F6 KeyDown, KeyUp.

Type Delete

KeyDown.

Change.

Text = Modified text

KeyUp.

Tab to next field

KeyDown.

in same record

BeforeUpdate.

Value = Text. Unbound controls

(or Form: Error)

also have OldValue = Text

(Program may cancel update)

AfterUpdate.

Exit, LostFocus.

Text property disappears

Next field gets: Enter,

GotFocus,KeyUp.

Click in next field

As tab to next field,

but no KeyDown event.

Move to next record

Form: BeforeUpdate.

(Program may cancel update)

Form: AfterUpdate.

All bound controlsin the form:

Database = OldValue = Value

Form: Current.

Click outside form

LostFocus.

(no action)

Click in form again

GotFocus.

(no action)

Click outside Access (no event)

foreUpdate procedure may cancel further event

processing so that the database is not updated.

If everything is okay, Access stores all the bound

control values in the database and in OldValue,

then calls the AfterUpdate procedure. Finally,

Access calls the Current procedure to signal that a

new record is selected.

User clicks outside the form, but inside the same

Access window. Access generates a LostFocus

event to show that typing will go to another object

in Access. In this case the Text property does not

disappear.

User clicks in form again. The active text box

receives a GotFocus event. The Text property has

survived.

User clicks outside Access. The text box does not re-

ceive any events (except for MouseMove events).

All properties survive. When the user clicks on the

Form again - even on the title bar - focus will be

back at the text box, but it receives no events at that

point.

The OldValue property allows the program to undo

changes to bound controls until the moment when the

form receives an AfterUpdate event. To undo a change,

the program sets Value=OldValue.

Key Preview. In some cases we want a key or key

combination to perform the same thing no matter

which control is selected. One example is function

keys. For instance we may want F2 to mean Reset

Criteria no matter where in the form the cursor is. This

can be handled by letting the Form look at the key

before any control gets to know about it. See section

5.5.9 for this Key Preview function.

5. Access through Visual Basic

5.3 Visual Basic tools

Before we go on writing more complex event proce-

dures, we will show some tools that Visual Basic of-

fers.

1. Open a form in Design mode. Now click the Code

icon on the toolbar (close to the Toolbox icon).

You are now in the Visual Basic window. (You might

also get there by choosing an event procedure in the

property box, as we did above.)

Docking and undocking, Access 2000 and 2003

The Visual Basic window may contain many frames. In

Access 2000 and 2003, they may be docked inside the

window or undocked, i.e. floating as separate small

windows. By accident you may dock or undock them,

and it may be very frustrating trying to get them back

where you want. So better learn how to deal with it:

2. Make sure the Visual Basic window occupies only

part of the screen.

3. Make sure the Docking settings are all on: Go to

Tools -> Options -> Docking and make sure that all

the checkboxes are set. Close the option box.

4. Click the Project Explorer icon. The window may

now look like Figure 5.3A with a list of forms at the

left (the Explorer frame) and some program code at

the right. However, it may also show only the Ex-

plorer frame, or show the Explorer frame as a small,

floating window.

5. Drag the Explorer frame to somewhere outside the

Visual Basic window. The Explorer frame is now

undocked.

6. Drag the Explorer frame to somewhere inside the

Visual Basic window. The frame will dock some-

where along a side of the window. Where it docks

does not depend on where the frame is when you

release the mouse button. It depends on where the

mouse pointer is when you release the button.

7. Try dragging the frame around in the Visual Basic

window. Notice that when the mouse pointer is

close to one of the sides, the frame changes to a thin

line showing the new shape of the frame. Release

the button to dock the frame accordingly.

8. Try double-clicking the title bar of the frame. The

frame toggles between docked and undocked.

Leave it docked as on Figure 5.3A.

Project Explorer

To the left you see a list of all forms in the database. In

object-oriented terminology, each form is a class. The

class has a code module with event procedures for the

controls on the form. When you double-click a form on

the list, you will see the code module to the right in the

Visual Basic window.

The database may also contain code modules (classes)

that are not forms. They are shown at the bottom of the

Project Explorer list.

All code modules may contain procedures and declare

variables. VBA offers three kinds of modules:

Form module. A form module has event procedures

for all controls on the form, and it may have ordi-

nary procedures too. It may declare variables.

When you open a form, you get an object based on

the form class. The object is a visible form and it

has a set of variables corresponding to the declara-

tions.

You cannot open several versions of the form just by

clicking multiple times in the database window, but

you may do it from Visual Basic. Then you get more

form objects, appearing as other open copies of the

form. Each copy has its own variables, but the same

code. When the code uses addresses such as

Me.txtName, it refers to the controls and variables of

this particular copy of the form.

When you create a form, you don't get its form module

until you create its first event procedure.

Class module. A class module corresponds to a class

in other object-oriented languages. It has proce-

dures and declares variables, and you can create

multiple objects based on the class, each with their

own variables. The only difference between form

modules and class modules is that the latter are not

visible to the user and have no controls.

See section 5.7 on how to create modules.

Module (simple). A simple module is similar to a class

but there is only one object based on the module.

The system creates this object automatically. The

first versions of Visual Basic had no class modules,

only simple modules.

Code window

To the right in the Visual Basic window, you see the

code window with the Visual Basic program. Figure

5.3A shows the code module for frmFindStay. You see

three event procedures for the txtName control. You

can scroll to other event procedures and controls, or

you can select them by means of the two combo boxes

at the top.

Creating an event procedure. Initially, the event pro-

cedures are not in the code, but if you select one of

them by means of the combo boxes, Visual Basic cre-

ates it. The same thing happens if you select an event

procedure through the control's property window.

However, Access doesn't always coordinate these two

things. You may experience that you have created an

event procedure in the code window, but it doesn't

appear in the property box. As a result, Access never

calls the event procedure. This may for instance happen

5. Access through Visual Basic

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