What's the difference between MODAL and MODELESS forms?
MODAL forms are forms which require user input before any other
actions can be taken place. In other words, a modal form has exclusive
focus in that application until it is dismissed. When showing a modal
form, the controls outside this modal form will not take user
interaction until the form is closed. The internal MsgBox and InputBox
forms are examples of modal forms. To show a form modally, use the
syntax:
MyForm.SHOW vbModal 'a predeclared
constant for 1
MODELESS forms are those which are shown but do not require immediate
user input. MDI child forms are always modeless. To show a form
modeless, use the syntax:
MyForm.SHOW
When/Why should I use Option Explicit?
Option Explicit forces you to declare all variables before using
them. Opinions vary greatly on this subject. The main reason to use the OPTION
EXPLICIT statement at the top of all modules is to minimize
the amount of bugs introduced into your code by misspelling a variable
name. Most variants of BASIC (including VB) have the capability to
create variables 'on the fly' (without any declarations). This
capability can be a double edged sword.
The OPTION
EXPLICIT statement causes VB to 'disable' its ability to
create variables on the fly. Thus, all variables must be declared using
a DIM or REDIM statement. All variables not declared will cause an error
when the OPTION
EXPLICIT statement is used. This will eliminate bugs caused
by a misspelled variable. The option works module-wide, so you can have
some modules with and some without this option in your project.
Declaring variables "on the fly" makes all but the most
trivial code difficult to debug and maintain.
VB creates Variant type variables by default.
Why does everybody say I should save in TEXT not BINARY?
Applies only to VB 3.0 and below: Actually, saving in binary
mode is a bit faster, so why do we recommend you to save in text?
If you save the source and the project as text, it becomes ASCII (or
really, ANSI) code that you can edit with any text editor or (if you are
careful when you save) word processor. If you save in binary, only the
VB development environment, current or later versions, will understand
the code. The Setup Wizard can not scan binary projects. Also, source
documenters and other programming tools usually require text mode. If
you use text, you can use a simple text editor (e.g. notepad) to cut and
paste code from other source/form modules into your current project.
Some 'tricks' (like making an array of 1 control into a single non-array
control again) is easily done with an editor but not that easy in the
environment. If you want to print your project to paper the file|print
option in the VB environment is often not good enough; you may want to
import the text files into your word processor. And, finally, if
something goes wrong (only one byte is changed!) you may be out of luck
in binary mode. In text mode you will more easily be able to fix it.
VB 4.0 and 5.0 does not offer the option of saving in binary, saving
us from a lot of problems.
Is the Variant type slower than using other variable types?
Generally, yes, if we are talking numeric variable types. The Variant
type also increases memory overhead. To test the speed difference, try
the following piece of code in something like a button_click event and keep the debug
window on the screen:
See code
This test shows (on our test system using VB 4.0) that integers are
~60% faster! However, for strings there where no real difference, or in
some instances, variants were faster than strings for routines with
heavy conversion usage. For the best result in your application, test
your routines directly.
How do I make a text box not beep but do something else when I hit
the Enter key?
Put "something else" in your _KeyPress event, depending on
what you really want. This code example makes nothing happen,
for an extended period of time:
Sub Text1_KeyPress (KeyAscii As
Integer)
If KeyAscii = 13 Then '13 is
Key_Return
KeyAscii = 0
End
If
End Sub
This might not be a very nice thing to do, since your users usually
have some intention when they press Enter. Often they will want to jump to the
next control, like the Tab
key does. To have the Enter
key emulate the Tab key action, you will need to add the line 'SendKeys
"{tab}"' above 'KeyAscii=0'
in the example above (Yes, I thought KeyAscii=9 works but it
doesn't! Tab
is obviously handled by Windows on a lower level).
By the way, you'll also find this in the Microsoft VB Knowledge Base
(see KB Q78305
and Q85562).
Note: If MultiLine=True
you will not want to disable the normal behaviour of the Enter
key.
How do I implement an incremental search in list/dir/combo/file
boxes?
This is your lucky day. Dan Champagne (Dan_Champagne@dell.com)
made some VB code (no DLLs are necessary!) which easily provides this
feature for your applications: See
code
How do I get the Tab key to be treated like a normal character?
You must set TabStop
= False for ALL controls on the active form. Then the user
will be able to insert Tab
(chr 9) characters in controls like the text box.
If you feel you need the Tab
key to behave like "normal" (e.g. jump to next control)
outside this specific control, it is trivial to emulate its
functionality in code:
Sub Command1_KeyDown (KeyCode As
Integer, Shift As Integer)
If KeyCode = 9 Then
If
Shift = 0 Then
Command2.SetFocus 'Tab=Next control
ElseIf Shift = 1 Then
Command3.SetFocus
'Shift-Tab=Prev.ctrl.
End If
End
If
End Sub
...etc.
How do I make an animated icon for my program?
For an example on how you change the icon for your application as it
is displayed when it is minimized, see the example REDTOP in the
\samples\picclip directory for VB/Win 3 Pro. This demonstrates a sort-of
fancy animated icon.
What is passing by reference?
Arguments are either passed by reference or by value. When they are
passed by value, they cannot be changed by the procedure or function
they are passed to. They can be altered when passed by
reference, since passing by reference is just passing the address.
Note that procedures are less strict about variable types when you
use BYVAL.
If you declare that your Sub takes a Variant, VB takes that seriously
and gives a nasty "mismatch error" if you try to pass e.g. a
string to it. Make it ByVal (at the cost of some speed) and your sub
will be more tolerant.
Also note the following nasty trap: Arguments are passed by reference
unless enclosed by parentheses or declared using the ByVal keyword. [VB
3.0 Language Ref., p. 55]
I get a "file not found" error on the IIF function when I
distribute by program. Uh?
There's a documentation error in VB 3.0, since the manual does not
tell you that the IIF
function requires the file MSAFINX.DLL to be distributed with your
application. No, IIF
is not really a financial function so go figure.
Is there any way to pass a variable to a form apart from using
global variables?
The standard workaround is to put an invisible text box (or caption
or any other control that suits your use.) on the target form and access
it by Form.textbox = "value". Then you can use the Change
event of that control to do anything you want in that form. Also, check
out the .Tag property which is a "what-you-want" property
where you can hook any string you want onto a control. This property can
also be accessed from other modules.
[Dave Mitton <mitton@dave.enet.dec.com>]
Perhaps a more elegant and flexible way is to implement a stack with
similar routines. I've done this for a math project, but this stack was
rather complicated and special purpose (and inspired by HP calculators,
of which I'm a great fan).
Jan G.P. Sijm <jan.sijm@intouch.nl>
has implemented some routines for general stacks: See
code
How should dates be implemented so they work with other language and
country formats?
If you use e.g. MM/DD/YY format dates in a program, you will get
either a runtime-error (e.g. month>12) or the wrong date (e.g. March
12 instead of December 3) when your program is used in Europe. And vice
versa, of course. Even Microsoft's own example programs (like the MAPI
sample in VB3) make this stupid mistake and fail miserably. Use the
Format command to make sure you get the date you want. For example:
strTodaysDate = Format[$](Now,
"Short Date")
As a side note, Microsoft has taken much heat on the newsgroup for
VB's bad support for internationalization! Just try to make a date
literal in source code that works everywhere as a little exercise.
Answer elsewhere in this document. No prizes :-)
Can a VB application be an OLE server?
No. Well, in VB 4.0 and 5.0 you can create OLE DLLs (OCXes) which
sort-of qualifies.
How do I dial a phone number without using the MSCOMM VBX?
[32-bit] For 32-bit programming, you can call the phone dialer
directly through the API. If you make a standard one-form project with
two buttons (Ok, Cancel), and two text boxes (txtName and txtNumber),
you can use the following code to dial a number:
Private Declare Function tapiRequestMakeCall Lib "TAPI32.DLL" _
(ByVal DestAddr$, ByVal AppName As String, _
ByVal CalledParty As String, ByVal Comment As String) As Long
Public Sub CallPhone(Number As String, Name As String)
Dim lRes As Long
If (Trim(Number) = "") Then
MsgBox "Sorry, no phone number defined"
Exit Sub
End If
If (MsgBox("About to call " & Trim(Name) _
& " at phone number " & Trim(Number) & vbCrLf & "Do it?", _
vbYesNo, App.Title) = vbYes) Then
lRes = tapiRequestMakeCall(Trim(Number), App.Title, Trim(Name), "")
Debug.Print Now; " CallPhone -> tapiRequestMakeCall Result code = "; lRes
End If
End Sub
Private Sub btnCancel_Click()
Unload Me
End Sub
Private Sub btnDial_Click()
CallPhone txtNumber.Text, txtName.Text
End Sub
This information provided by Peter Ibbotson <peter@ibbotson.demon.co.uk>
For a more rough approach, try the following code:
PhoneNumber$ =
"(123)456-7890"
Open
"COM2:" For Output As #1 'or COM1
Print
#1, "ATDT" & PhoneNumber$ & Chr$(13)
Close
#1
Ian Storrs <exuian@exu.ericsson.se>
first informed me that he had experienced problems with this when the VB
program was run from a network drive. A file named "COM1" was
created on the disk! Jeff Rife <jrife@health.org>
was the one to put in the ":" after COM2 to solve that
problem!
This trick is probably not a good idea for bigger applications, but
it's nice for small personal utilities.
I have [several] megabytes of memory. Why do I get an "out of
memory" error?
This problem and its solution(s) are not applicable to
Windows 95, but only Windows 3.x. If you receive this error
using Win95 or NT, it will probably be the wrong error message for some
other problem.
Unfortunately, Microsoft has earlier been more famous for memory
barriers than anything else. This is a late descendant of the infamous
640K barrier that has been plaguing us for years. Although Windows
allows the user to access several megabytes of memory, it uses two
limited (64K) memory areas called User Heap and GDI Heap for some
specific data structures. Go to the Help|About box in Program Manager to
see the percentage of free resources in the most exhausted
heap. If these areas are exhausted, you are out of luck. VB programs are
unfortunately rather greedy on these structures. Windows 4 is supposed
to free us from this limitation...
Note that every visible control (ie every button) is a window to
Windows. Every new control takes up some bytes in the precious User
heap.
Also, there is another way to run out of memory in Windows, not
related to VB. Windows requires free Upper Memory Area (UMA, also called
Upper Memory Blocks, not to be confused with High RAM, which is the
first 64K of extended memory) to do certain tasks. If you use QEMM or
DOS 6+ MemMaker and you have many device drivers (network, etc) this
area may have been filled up before you launch Windows. You will then be
unable to start applications, even though you have plenty of free RAM.
The problem can be solved with careful memory setup, but this is far
beyond the scope of this FAQ.
On a completely unrelated problem: When you run a program with an
outline control with some ATI graphics cards, it may crash with just
that error message. (see Knowledge Base Q100194
PRB: "Some ATI Video Drivers Hang When Using MSOUTLIN.VBX"). I
assume this problem is fixed both from ATI and Microsoft now.
How do I mimic a toggle button?
The only "fix" we know for this problem is to use a picture
or image control to mimic the action of a button or button3d control.
You need two bitmaps, one for buttonup and one for buttondown (and
perhaps one more for inactive state). This is a kluge, we know. Look at
the button bar used in the MDINOTE sample program supplied with VB for
an example of this.
How do I get my application on top?
To make your window truly topmost, use the SetWindowPos API call.
First, make these declares:
#IF WIN32 THEN
Declare Function SetWindowPos Lib
"user32" Alias "SetWindowPos" _
(ByVal hwnd As Long, ByVal hWndInsertAfter As Long, _
ByVal x As Long, ByVal y As Long, ByVal cx As Long, _
ByVal cy As Long, ByVal wFlags As Long) As Long
#ELSE 'Win16
Declare Sub SetWindowPos Lib
"User" (ByVal hWnd As Integer, _
ByVal hWndInsertAfter As Integer, ByVal X As Integer, _
ByVal Y As Integer, ByVal cx As Integer, ByVal cy As Integer, _
ByVal wFlags As Integer)
#END IF
Global Const SWP_NOMOVE = 2
Global Const SWP_NOSIZE = 1
Global Const FLAGS = SWP_NOMOVE Or SWP_NOSIZE
Global Const HWND_TOPMOST = -1
Global Const HWND_NOTOPMOST = -2
To set Form1 as a top-most form, do the following:
#IF WIN32 THEN
Dim lResult as Long
lResult = SetWindowPos (me.hWnd, HWND_TOPMOST, _
0, 0, 0, 0, FLAGS)
#ELSE '16-bit API uses a Sub, not a
Function
SetWindowPos me.hWnd, HWND_TOPMOST, _
0, 0, 0, 0, FLAGS
#END IF
To turn off topmost (make the form act normal again), do the
following:
#IF WIN32 THEN
Dim lResult as Long
lResult = SetWindowPos (me.hWnd, HWND_NOTOPMOST, _
0, 0, 0, 0, FLAGS)
#ELSE '16-bit API uses a Sub, not a
Function
SetWindowPos me.hWnd, HWND_NOTOPMOST, _
0, 0, 0, 0, FLAGS
#END IF
If you don’t want to force a window on top, which will prevent the
user from seeing below it, but simply want to move a Window to the top
for the user’s attention, do this:
Form1.ZOrder
You can, to make the application stay on top, put the ZOrder method
in a Timer event repeatedly called, say, every 1000 milliseconds. This
makes a "softer" on-top than other methods, and allows the
user to make a short peek below the form.
There are two different Zorder’s of windows (forms) in Windows,
both implemented internally as linked lists. One is for
"normal" windows, the other for "topmost" windows
(like the Clock application which is distributed with Windows). The
ZOrder command above simply moves your window to the top of the
"normal" window stack. There is another, independent stack for
topmost windows – like those created by the example code above –
which resolves problems if several of those should conflict.
Note that when a form is minimized, it loses its topmost attribute
and you will have to set it again.
Is there a way to break long lines in VB code?
Visual Basic 4.0 and above breaks any lines by placing " _"
(space+underscore) at the end of the line which will continue below. You
cannot break inside literals (ie. quotes). This was a much welcome
addition!
For earlier VB versions, the answer is you can't break long lines.
This feature first came with Excel 5 VBA.
There are a few tricks you can use to reduce line length, but
unfortunately there is very little to do with DECLARE statements which
can get very long. Still: Print your source in landscape :-/
How do I remove/change the picture property of a control at design
time?
Workaround for VB 3.0 bug: Mark the (bitmap) or (icon) text
in the property window and press Del
or Backspace.
"No!" I hear you cry, "It doesn't work". Well, it
does if you first select the object from the combo box at the top of the
Properties Window, and then immediately afterwards doubleclick (or paint
over) the "(bitmap)" text and press Del. Alternatively, just click
on another control, then click back to the first control. Now Del
works. Who said "bug"?
If you want to paste your picture directly into the VB program by
pressing Ctrl-V
when you are editing the picture property, you will have to use a
semilar procedure: select the control, select the property, press Ctrl-V. If you try it again
without deselecting the control first (or selecting it from the combo
box), it doesn't work.
How do I make my applications screen-resolution independent?
There are two methods: Either get a custom control that does the job
for you, or you write lots of complicated code in the Load and Resize
events.
For the first option, check out VideoSoft's $hareware VSVBX.VBX/OCX.
Go to http://www.videosoft.com
for updated info. It has a will of its own, as you will experience, but
it's generally better than trying what is described below.
For the brave (or stupid), try to write "screen resolution-smart
code" in the form's Load event. If the form is resizable (normally
it should be), you'll have to put some magic into the Resize event as
well. There are 4 rules of thumb:
- Do not trust the form's height
and width
properties. These measure the entire form, not the client area where
your controls are. To see this in action, create a simple applet
with the only code being in the resize event which resets a line
control from 0,0 to the form's width,height properties. The top left
corner is in the client area, the bottom right corner disappears.
The API call GetClientRect will return the size of the client area
in pixels. You can use the screen object's TwipsPerPixelX
and TwipsPerPixelY
properties to convert from pixels to twips. If that's not enough,
GetWindowRect will return the actual size of the entire form, client
and non-client areas combined. GetSystemMetrics
will return individual pieces of things like border width/hight,
caption height, etc.
- Use the TextWidth
and TextHeight
properties. You can use them off the form if all your controls share
the same font, otherwise use them off of the given control. I
typically do a TextWidth("X")
and TextHeight("X")
to get a value which I use as a margin between controls. I grab
these values on startup, and multiply it by 2, 1.5, .75, .5, .25 to
get varying margin sizes, depending on how close or far apart I want
to space things. If your control has an autosize property, you may
want to use it, and then calculate the maximum width of a control in
a given "column" of controls on your screen and position
all of them accordingly.
- Try not to resize your
controls in the resize event. You will spawn another resize event in
the process. Of course, you can use a flag to determine whether the
resize event is the original event or the spawned one. Using the load
event, and setting the forms borders to fixed minimizes the amount
of work you have to do.
- Make sure you use a
consistant scale. I don't even bother with the scale properties, but
instead just convert pixels (from API calls) into twips and be done
with it. If you do use scale properties, be sure you convert your
numbers correctly. I had no end of difficulty when I failed to
convert into twips with one number that was used in a series of
calculations to position controls. Also be sure all your controls
share the same SCALE -- another nasty problem I had before I gave up
on them completely.
[Thanks to our generous anonymous source "D"]
How do I do Peek and Poke and other low-level stuff?
VB provides no direct mechanism for this.
On The Microsoft Developer Network Library CD, you’ll find a
utility called VBASM which provides full access to all
sorts of low-level routines: peek, poke, memory pointer, port i/o and
interrupts. You should be able to find vbasm.dll easily
by searching for it on the net.
[Deane Gardner
<deaneg@ix.netcom.com> quotes Microsoft]
There are several 3rd party packages which provide this
functionality. Also, this often comes up in regards to the communication
ports and you can many times do what you want with the MsComm control
(which comes with the professional/enterprise editions of VB).
Why doesn't "my string" & Chr$(13) do what I want?
You need to also add a Chr$(10):
"my
string" & Chr$(13) & Chr$(10) will give you a
CR and LF.
[George Tatge (gat@csn.org)]
There are constants that make this more readable: "my
string" & vbCrLf and "mystring"
& vbCR & vbLF both equals the above.
How do I prevent multiple instances of my program?
In VB 3 and above, the property App.PrevInstance is set to True if an
older instance of the program already exist.
This
following piece of code, stolen from MS KB article Q102480,
will activate the old instance and then terminate itself.
As Robert Knienider(rknienid@email.tuwien.ac.at) informed me, this
piece of code will not work for non-English versions of
Mirosoft Windows where the word for "Restore" does not have
"R" as the underlined word. Replace the "R" in the
SendKeys line above with "{ENTER}"
or "~".
Note that you shouldn't prevent multiple instances of your
application unless you have a good reason to do so, since this is a very
useful feature in MS Windows. Windows will only load the code and
dynamic link code once, so it (normally) uses much less
memory for the later instances than the first.
How do I implement an accelerator key for a text box?
You want to use a label caption to identify a text box and to act as
if it were the text box caption:
Example:
&Label1 [text1 ]
How should I do to set the focus to text1, by typing <ALT>L
Make sure that the TabIndex property for the text box is 1 greater
than the label's TabIndex.
Since a label can't have the focus, the focus will go to the next item
in the tab order, which would be the text box.
Here's any easy way to set the TabIndex for a busy form. Select the
object that should be last in the tab order and then select the TabIndex
property. Press 0 (zero), click on the next to last object, press 0,
click on the the next object back, press 0, etc. When you're done, all
of the TabIndexes will be in order, because VB increments all of the
higher TabIndexes when you put in a lower number.
Many thanks to Jonathan Kinnick and Gary Weinfurther that provided
the answer on the FIDO net echo VISUAL_BASIC.
[Tiago Leal (Tiago.Leal@p25.f1.n283.z2.gds.nl)]
How do I force a file list box to reread the current disk?
If you make a simple dialogue box modelled after common dialogue
(normally you should use the common dialogue control), you will
notice that reselecting the diskette drive will not really rescan the
disk. Very annoying to change to C:,
and to reselect A:
just to make it read the directory of a new diskette.
To solve this problem, put
drive1.refresh
dir1.refresh
file1.refresh
in the code for the "Reread" button (or whatever).
How do I get the number of free bytes on a disk?
See Article Q113590
(or Q106553)
in Microsoft's VB KnowledgeBase. A short extract follows:
Declare Function DiskSpaceFree Lib
"SETUPKIT.DLL" () As Long
Dim free_space& 'Holds number of bytes returned from
DiskSpaceFree().
ChDrive "c:" 'Change to the drive you want to test.
free_space& = DiskSpaceFree()
[Geir Tutturen <itfgt@nlh10.nlh.no>]
As far as I know, there are three possibilities:
- SETUPKIT.DLL as mentioned
above
- Arjen Broeze's VBIO.VBX or
something like that, with a lot of options.
- Make your own DISKINFO.DLL
from the example code in VBKB article Q106553.
Data Control missing from toolbox when I use VB under NT 3.5. Huh?
Applies to VB 3.0 with Windows NT 3.5: Open the VB.INI file
and add these lines under the [Visual Basic] heading:
ReportDesign=1
DataAccess=1
[Danny Ames<dames@pic.net>]
How do I avoid the overflow error when assigning values to my
variable?
Be wary of the scopes of variables. In particular, be wary of the Integer.
It accepts values from -32,768 to 32,767. Anything else causes an
overflow run-time error:
i% = 30000 + 30000 'fails
There is little reason to not use the Long data type
instead, which brings us to some other, more subtle problem. Try this:
l& = 30000 + 30000 'fails. Huh?
The reason for this very odd problem is that VB evaluates the
expression internally, using the type of the constants, and in this case
it's still Integer. So the run-time error occurs even before it tries to
assign the value to the Long type variable. To make it work, you
have to do the following:
i&=30000& + 30000& 'ok
While the Long uses two bytes more internal space, this is nothing to
worry about. Since the 32-bit CPU actually works with 32-bit long
integers internally, it is even a (theoretical) bit faster than the
shorter counterpart. So if in doubt, and even if not, stick to Longs.
[PET PEEVE] Why doesn't VB provide an unsigned integer, which can
take values from 0 to 65,535? This is a major omission.
[NOTE] Some perfectly sane programmers prefer to create their VB
applications using the Variant data type almost
exclusively. While that would not solve the actual problem above, it
certainly will remove most type-conversion and mismatch problems with
VB. The extra execution time and memory overhead is rarely significant.
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