I frequent the various Microsoft-sponsored VB news groups and from time to time, I've seen posts requesting help with the Shell command. Some people want to pause their application until the program that they spawned no longer is running. Presumably, they are writing a helper app, or a training tool, or a data processing gizmo that depends upon the spawned service to create some information.
Other people are spawning DOS applications. Generally, they want this to be transparent to the end user, and they really don't want anyone to know that a DOS application is doing something. Maybe it needs to be hidden so that the user can't interact with the DOS app.
Regardless of the reason, waiting for and hiding spawned applications is something that you may find yourself needing to do. The Shell command isn't especially well suited for the task.
The SuperShell example that I have written addresses all of these needs and then some. Your application will be frozen until the wait time that you have set has elapsed. You can start the spawned application hidden, minimized, maximized, or normally. And finally, you can set the task priority for the program, giving the spawned application more priority (or speed) than it would have otherwise.
If you select HIDDEN as your window style, you will NOT be able to shut the spawned application down. Be careful when using a hidden window style and an INFINITE or long wait time.
I originally wrote the SuperShell command to take Optional auguments. As it turns out, optional auguments seem to have problems when more than one is sent, so I removed this support. Perhaps an update of VB 5 will address this problem.
Option Explicit Public Const INFINITE = &HFFFF 'STARTINFO constants Private Const STARTF_USESHOWWINDOW = &H1 Public Enum enSW SW_HIDE = 0 SW_NORMAL = 1 SW_MAXIMIZE = 3 SW_MINIMIZE = 6 End Enum Private Type PROCESS_INFORMATION hProcess As Long hThread As Long dwProcessId As Long dwThreadId As Long End Type Private Type STARTUPINFO cb As Long lpReserved As String lpDesktop As String lpTitle As String dwX As Long dwY As Long dwXSize As Long dwYSize As Long dwXCountChars As Long dwYCountChars As Long dwFillAttribute As Long dwFlags As Long wShowWindow As Integer cbReserved2 As Integer lpReserved2 As Byte hStdInput As Long hStdOutput As Long hStdError As Long End Type Type SECURITY_ATTRIBUTES nLength As Long lpSecurityDescriptor As Long bInheritHandle As Long End Type Public Enum enPriority_Class NORMAL_PRIORITY_CLASS = &H20 IDLE_PRIORITY_CLASS = &H40 HIGH_PRIORITY_CLASS = &H80 End Enum Private Declare Function CreateProcess Lib "kernel32" Alias "CreateProcessA" _ (ByVal lpApplicationName As String, ByVal lpCommandLine As String, _ lpProcessAttributes As SECURITY_ATTRIBUTES, lpThreadAttributes As _ SECURITY_ATTRIBUTES, ByVal bInheritHandles As Long, ByVal _ dwCreationFlags As Long, lpEnvironment As Any, ByVal lpCurrentDriectory _ As String, lpStartupInfo As STARTUPINFO, lpProcessInformation _ As PROCESS_INFORMATION) As Long Private Declare Function WaitForSingleObject Lib "kernel32" _ (ByVal hHandle As Long, ByVal dwMilliseconds As Long) As Long Public Function SuperShell(ByVal App As String, ByVal WorkDir As String, _ dwMilliseconds As Long, ByVal start_size As enSW, ByVal Priority_Class _ As enPriority_Class) As Boolean Dim pclass As Long Dim sinfo As STARTUPINFO Dim pinfo As PROCESS_INFORMATION 'Not used, but needed Dim sec1 As SECURITY_ATTRIBUTES Dim sec2 As SECURITY_ATTRIBUTES sec1.nLength = Len(sec1) sec2.nLength = Len(sec2) sinfo.cb = Len(sinfo) sinfo.dwFlags = STARTF_USESHOWWINDOW sinfo.wShowWindow = start_size pclass = Priority_Class If CreateProcess(vbNullString, App, sec1, sec2, False, pclass, _ 0&, WorkDir, sinfo, pinfo) Then WaitForSingleObject pinfo.hProcess, dwMilliseconds SuperShell = True Else SuperShell = False End If End Function
Supershell returns TRUE if it successfully spawned the application. If you have a wait time defined, you aren't going to get notification until after the spawned application terminates or the sleep time (dwMilliseconds) elapses. As a result, you may want to set a variable with the current time and check it when you return. Also, you will probably want to shutdown all timers and similar controls that can be sent messages generated outside of your application.
If you want to wait forever, set dwMillisecond to INFINITE (a public constant). Again, I caution you not to do that while spawning a hidden application, not unless you are sure that it will return control back to your program.
Finally, I should mention that you should hide the calling application. As you will soon discover, if you wait for a task to conclude, your program will not even repaint, which gets very ugly on-screen. Looks kinda cool though I doubt that users will appreciate it!
If you are interested into delving a little deeper into the CreateProcess function, you will find that with a little work you can add several other things which I elected not to implement. For instance, you can specify the exact location and size of the spwned application, down to the pixel.
Originally written by Tim Kilgore.