Declare Function WaitForSingleObject Lib "kernel32.dll" (ByVal hHandle As Long, ByVal dwMilliseconds As Long) As Long
WaitForSingleObject halts program execution temporarily, until either a specified object enters a signaled state or a specified timeout period elapses. This function allows a program to wait until something else has happened before execution continues.
The function returns one of the following flags:
None.
Const WAIT_ABANDONED = &80 Const WAIT_FAILED = &HFFFFFFFF Const WAIT_OBJECT_0 = &H0 Const WAIT_TIMEOUT = &H102 Const INFINITE = &HFFFF
Open the file "C:\Docs\readme.txt" using whatever program is associated with *.txt files (by default, Notepad). Wait until the user has closed the window before continuing with the example. The example begins when the user clicks button Command1. Obviously, to use this example, you need to place a command button named Command1 on a form window.
' This code is licensed according to the terms and conditions listed here. ' Declarations and such needed for the example: ' (Copy them to the (declarations) section of a module.) Public Type SHELLEXECUTEINFO cbSize As Long fMask As Long hwnd As Long lpVerb As String lpFile As String lpParameters As String lpDirectory As String nShow As Long hInstApp As Long lpIDList As Long lpClass As String hkeyClass As Long dwHotKey As Long hIcon As Long hProcess As Long End Type Public Const SEE_MASK_NOCLOSEPROCESS = &H40 Public Const SW_SHOWNORMAL = 1 Public Declare Function ShellExecuteEx Lib "shell32.dll" Alias "ShellExecuteExA" (lpExecInfo As _ SHELLEXECUTEINFO) As Long Public Const SE_ERR_FNF = 2 Public Const SE_ERR_NOASSOC = 31 Public Declare Function WaitForSingleObject Lib "kernel32.dll" (ByVal hHandle As Long, ByVal _ dwMilliseconds As Long) As Long Public Const INFINITE = &HFFFF Public Const WAIT_TIMEOUT = &H102 ' *** Place the following code inside window Form1. *** Private Sub Command1_Click() Dim sei As SHELLEXECUTEINFO ' structure used by the function Dim retval As Long ' return value ' Load the information needed to open C:\Docs\readme.txt ' into the structure. With sei ' Size of the structure .cbSize = Len(sei) ' Use the optional hProcess element of the structure. .fMask = SEE_MASK_NOCLOSEPROCESS ' Handle to the window calling this function. .hwnd = Form1.hWnd ' The action to perform: open the file. .lpVerb = "open" ' The file to open. .lpFile = "C:\Docs\readme.txt" ' No additional parameters are needed here. .lpParameters = "" ' The default directory -- not really necessary in this case. .lpDirectory = "C:\Docs\" ' Simply display the window. .nShow = SW_SHOWNORMAL ' The other elements of the structure are either not used ' or will be set when the function returns. End With ' Open the file using its associated program. retval = ShellExecuteEx(sei) If retval = 0 Then ' The function failed, so report the error. Err.LastDllError ' could also be used instead, if you wish. Select Case sei.hInstApp Case SE_ERR_FNF Debug.Print "The file C:\Docs\readme.txt was not found." Case SE_NOASSOC Debug.Print "No program is associated with *.txt files." Case Else Debug.Print "An unexpected error occured." End Select Else ' Wait for the opened process to close before continuing. Instead ' of waiting once for a time of INFINITE, this example repeatedly checks to see if the ' is still open. This allows the DoEvents VB function to be called, preventing ' our program from appearing to lock up while it waits. Do DoEvents retval = WaitForSingleObject(sei.hProcess, 0) Loop While retval = WAIT_TIMEOUT Debug.Print "Notepad (or whatever program was opened) has just closed." End If End Sub
See Also --> Synchronization
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Last Modified: October 29, 2000
This page is copyright © 2000 Paul Kuliniewicz. Copyright Information Revised October 29, 2000
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