You can use the Windows API ShellExecute() function to start the
application associated with a given document extension without knowing the
name of the associated application. For example, you could start the
Paintbrush program by passing the filename ARCADE.BMP to the ShellExecute()
function.
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The ShellExecute function opens or prints the specified file. Following is
the declaration to use when calling this function from Visual Basic:
Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" _
(ByVal hwnd As Long, ByVal lpszOp As String, _
ByVal lpszFile As String, ByVal lpszParams As String, _
ByVal LpszDir As String, ByVal FsShowCmd As Long) _
As Long
The following table provides descriptions for each parameter:
Parameter Description
----------------------------------------------------------------------------
hwnd Identifies the parent window. This window receives any
message boxes an application produces (for example, for error
reporting).
lpszOp Points to a null-terminated string specifying the operation
to perform. This string can be "open" or "print." If this
parameter is NULL, "open" is the default value.
lpszFile Points to a null-terminated string specifying the file
to open.
lpszParams Points to a null-terminated string specifying parameters
passed to the application when the lpszFile parameter
specifies an executable file. If lpszFile points to a string
specifying a document file, this parameter is NULL.
LpszDir Points to a null-terminated string specifying the default
directory.
FsShowCmd Specifies whether the application window is to be shown when
the application is opened.
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Step-by-Step Example
The following example demonstrates how to start an application or load a
document into its associated application. The Windows API ShellExecute()
function is different from the Visual Basic Shell() function in that you
can pass the ShellExecute() function the name of a document and it will
launch the associated application, and then pass the filename to the
application.
| 1. | Start a New project in Visual Basic. Form1 is created by default.
|
| 2. | Add the following code to the General Declarations section of Form1:
Option Explicit
Private Declare Function ShellExecute Lib "shell32.dll" Alias _
"ShellExecuteA" (ByVal hwnd As Long, ByVal lpszOp As _
String, ByVal lpszFile As String, ByVal lpszParams As String, _
ByVal lpszDir As String, ByVal FsShowCmd As Long) As Long
Private Declare Function GetDesktopWindow Lib "user32" () As Long
Const SW_SHOWNORMAL = 1
Const SE_ERR_FNF = 2&
Const SE_ERR_PNF = 3&
Const SE_ERR_ACCESSDENIED = 5&
Const SE_ERR_OOM = 8&
Const SE_ERR_DLLNOTFOUND = 32&
Const SE_ERR_SHARE = 26&
Const SE_ERR_ASSOCINCOMPLETE = 27&
Const SE_ERR_DDETIMEOUT = 28&
Const SE_ERR_DDEFAIL = 29&
Const SE_ERR_DDEBUSY = 30&
Const SE_ERR_NOASSOC = 31&
Const ERROR_BAD_FORMAT = 11&
Function StartDoc(DocName As String) As Long
Dim Scr_hDC As Long
Scr_hDC = GetDesktopWindow()
StartDoc = ShellExecute(Scr_hDC, "Open", DocName, _
"", "C:\", SW_SHOWNORMAL)
End Function
Private Sub Form_Click()
Dim r As Long, msg As String
r = StartDoc("C:\WINDOWS\ARCADE.BMP")
If r <= 32 Then
'There was an error
Select Case r
Case SE_ERR_FNF
msg = "File not found"
Case SE_ERR_PNF
msg = "Path not found"
Case SE_ERR_ACCESSDENIED
msg = "Access denied"
Case SE_ERR_OOM
msg = "Out of memory"
Case SE_ERR_DLLNOTFOUND
msg = "DLL not found"
Case SE_ERR_SHARE
msg = "A sharing violation occurred"
Case SE_ERR_ASSOCINCOMPLETE
msg = "Incomplete or invalid file association"
Case SE_ERR_DDETIMEOUT
msg = "DDE Time out"
Case SE_ERR_DDEFAIL
msg = "DDE transaction failed"
Case SE_ERR_DDEBUSY
msg = "DDE busy"
Case SE_ERR_NOASSOC
msg = "No association for file extension"
Case ERROR_BAD_FORMAT
msg = "Invalid EXE file or error in EXE image"
Case Else
msg = "Unknown error"
End Select
MsgBox msg
End If
End Sub
|
| 3. | Run the project and click the form.
|
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General Information About the Process
If the function succeeds, the return value is the instance handle of the
application that was run. If there was an error, the return value is less
than or equal to 32.
The file specified by the lpszFile parameter can be a document file or an
executable file. If it is a document file, this function opens or prints it
depending on the value of the lpszOp parameter. If it is an executable
file, this function opens it even if the lpszOp specifies "PRINT."
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"Programmer's Reference, Volume 2: Functions" of the Microsoft Windows
Software Development Kit (SDK), pages 901-904
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