If Dir(Filename) <> "" Then - file exists

where FileName is the name of the file checked.

Declare Function SetWindowPos Lib "user32" (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

and the code for making the form stay on top is:

SetWindowPos Me.Hwnd, -2, 0, 0, 0, 0, &H1 Or &H2

and to make it back normal use:

SetWindowPos Me.Hwnd, -1, 0, 0, 0, 0, &H1 Or &H2

replace Me with another form name if you need.
Here is a description of the above values:

 

Value	Constant	Meaning
-2	HWND_TOPMOST	Form will stay on top
-1	HWND_NOTOPMOST	Form won't stay on top
&H1	SWP_NOSIZE	Do not resize the form
&H2	SWP_NOMOVE	Do not move the form
0,0,0,0		X, Y, Width, Height - ignored

Run URL


We will use ShellExecute API function which is usually used to run executables or other files associated with a given application to connect to an internet site. Declaration:

Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" (ByVal hwnd As Long, ByVal lpOperation As String, ByVal lpFile As String, ByVal lpParameters As String, ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long

and the code:

R& = ShellExecute(Me.hwnd, "Open", "http://geocities.datacellar.net/SiliconValley/Lab/1632/", "", App.Path, 1)

replace the internet address with the one you want.
Value description:

Value	Description
R&	error code returned if error occured
Me.Hwnd	a handle of a window to receive some kind of messages. You don't really need them.
"http ...."	the internet address
""	null string. Actually specifies any parameters if an EXE is run
App.Path	work directory
1	show the application run

Get Disk Free Space


We use GetFreeSpace API function.
Declaration:

Declare Function GetDiskFreeSpace Lib "kernel32" Alias "GetDiskFreeSpaceA" (ByVal lpRootPathName As String, lpSectorsPerCluster As Long, lpBytesPerSector As Long, lpNumberOfFreeClusters As Long, lpTtoalNumberOfClusters As Long) As Long

and the code looks something like that:

If GetDiskFreeSpace("d:\", SecPCl&, BytPSec&, FreeCl&, TotCl&) Then
MsgBox "Free Space - " & BytPSec& * SecPCl& * FreeCl&
MsgBox "Total Space - " & BytPSec& * SecPCl& * TotCl&
Else
MsgBox "Error"
End If

Value Descriptions:

Value	Description
"d:\"	the root directory of the disk. If NULL - the root of the current directory is assumed
SecPCl&	sectors per cluster
BytPSec&	bytes per sector
FreeCl&	number of free clusters
TotCl&	total number of clusters

Check For Another Instance Of Your App


It is very simple, just check App.PrevInstance. If it is True, then another instance is already running, else no other instances are available.


Wait Some Time


You have two choices here - VB code or API.
VB Code:

x! = Timer
Do Loop While Abs(Timer - x!) <= TimeInSeconds

or API:
Declaration:

Declare Sub Sleep Lib "kernel32" Alias "Sleep" (ByVal dwMilliseconds As Long)

to wait some time call:

Sleep(TimeInMilliSeconds)

Getting Windows And System Directories


There are two API functions for doing it - GetWindowsDirectory and GetSystemDirectory. Here are the declarations:

Declare Function GetSystemDirectory Lib "kernel32" Alias "GetSystemDirectoryA" (ByVal lpBuffer As String, ByVal nSize As Long) As Long
Declare Function GetWindowsDirectory Lib "kernel32" Alias "GetWindowsDirectoryA" (ByVal lpBuffer As String, ByVal nSize As Long) As Long

and the code:
Windows Directory:

S$ = Space(260)
SLen& = GetWindowsDirectory(S$, 260)
MsgBox Left(S$, SLen&)

System Directory:

S$ = Space(260)
SLen& = GetSystemDirectory(S$, 260)
MsgBox Left(S$, SLen&)

So S$ is initialized to be a string of 260 spaces (260 is currently the MAX length for a path). Then we pass it to the function and tell her its length as well. The function returns the actual length and we use it to clip the rest of the string (in fact the string we'll be something like: C:\WIN95 ... - spaces till 260 len and if you don't clip the rest after the NULL MsgBox S$ will display the same result, but MsgBox S$ & "some text" won't.