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Utilising the ShellExecute command to Open files

Posted on 2004-04-17
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Last Modified: 2012-06-21
Folks,

    I have a Visual Basic program that displays the contents of a folder. The folder can have both subfolders and files within it. When the user double clicks on the file - I want my program to open the file in its associated program. I have searched around and have come up with this ...

Declare Function ShellExecuteA Lib "shell32.dll" _
 (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


Now that is all well and good. And it does work. But I need to know what each of the variables mean and how I can get the best out of them - i.e add in further clauses to the opening of the file.

What I really want to do is lock the file for reading and writing when it opens. But dont know how!
I tried adding in :

   "Lock Read Write" for the value of 'ByVal lpParameters As String'

  But this doesnt appear to work. Maybe im doing it wrong.

  Can you help?

  Also - I need to know when the file is closed again i.e when the user has carried out his/her updates and has closed the file. Is that possible?


Thanks in advance,
     shanncan
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Question by:shanncan
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Accepted Solution

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AlexFM earned 125 total points
ID: 10851980
You cannot lock the file, it depends on the program associated with file. It may lock file or not. For example, text editors like Notepad don't lock file all time they are opened, only when file is loaded or unloaded.
You can know when the program associated with this file finished. To do this replace ShellExecute with ShellExecuteEx. It returns handle to created process in HANDLE hProcess member of SHELLEXECUTEINFO. You can wait for this process using WaitForSingleObject:

http://www.mangovision.com/vbapi/ref/s/shellexecuteex.html
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Expert Comment

by:jmeaux
ID: 10853867
Shanncan,

This info is from Microsoft's MSDN, which is freely accessible to everyone with Internet access at:
   msdn.microsoft.com

I have obtained your information from page:
   http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/shell/reference/functions/shellexecute.asp

Here is your anwser:

Parameters ********************************************************************************

hwnd
[in] Handle to a parent window. This window receives any message boxes that an application produces, such as error reporting.

lpOperation
[in] Pointer to a null-terminated string, referred to in this case as a verb, that specifies the action to be performed. The set of available verbs depends on the particular file or folder. Generally, the actions available from an object's shortcut menu are available verbs. For more information about verbs and their availability, see Object Verbs. See Extending Shortcut Menus for further discussion of shortcut menus. The following verbs are commonly used.
edit -Launches an editor and opens the document for editing. If lpFile is not a document file, the function will fail.
explore - Explores the folder specified by lpFile.
find - Initiates a search starting from the specified directory.
open - Opens the file specified by the lpFile parameter. The file can be an executable file, a document file, or a folder.
print - Prints the document file specified by lpFile. If lpFile is not a document file, the function will fail.
NULL - For systems prior to Microsoft® Windows® 2000, the default verb is used if it is valid and available in the registry. If not, the "open" verb is used.
For Windows 2000 and later systems, the default verb is used if available. If not, the "open" verb is used. If neither verb is available, the system uses the first verb listed in the registry.

lpFile
[in] Pointer to a null-terminated string that specifies the file or object on which to execute the specified verb. To specify a Shell namespace object, pass the fully qualified parse name. Note that not all verbs are supported on all objects. For example, not all document types support the "print" verb.

lpParameters
[in] If the lpFile parameter specifies an executable file, lpParameters is a pointer to a null-terminated string that specifies the parameters to be passed to the application. The format of this string is determined by the verb that is to be invoked. If lpFile specifies a document file, lpParameters should be NULL.

lpDirectory
[in] Pointer to a null-terminated string that specifies the default directory.

nShowCmd
[in] Flags that specify how an application is to be displayed when it is opened. If lpFile specifies a document file, the flag is simply passed to the associated application. It is up to the application to decide how to handle it.
SW_HIDE - Hides the window and activates another window.
SW_MAXIMIZE - Maximizes the specified window.
SW_MINIMIZE - Minimizes the specified window and activates the next top-level window in the z-order.
SW_RESTORE - Activates and displays the window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when restoring a minimized window.
SW_SHOW - Activates the window and displays it in its current size and position.
SW_SHOWDEFAULT - Sets the show state based on the SW_ flag specified in the STARTUPINFO structure passed to the CreateProcess function by the program that started the application. An application should call ShowWindow with this flag to set the initial show state of its main window.
SW_SHOWMAXIMIZED - Activates the window and displays it as a maximized window.
SW_SHOWMINIMIZED - Activates the window and displays it as a minimized window.
SW_SHOWMINNOACTIVE - Displays the window as a minimized window. The active window remains active.
SW_SHOWNA - Displays the window in its current state. The active window remains active.
SW_SHOWNOACTIVATE - Displays a window in its most recent size and position. The active window remains active.
SW_SHOWNORMAL - Activates and displays a window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when displaying the window for the first time.


Return Value ********************************************************************************

Returns a value greater than 32 if successful, or an error value that is less than or equal to 32 otherwise. The following table lists the error values. The return value is cast as an HINSTANCE for backward compatibility with 16-bit Windows applications. It is not a true HINSTANCE, however. The only thing that can be done with the returned HINSTANCE is to cast it to an int and compare it with the value 32 or one of the error codes below.

0 The operating system is out of memory or resources.
ERROR_FILE_NOT_FOUND - The specified file was not found.
ERROR_PATH_NOT_FOUND - The specified path was not found.
ERROR_BAD_FORMAT - The .exe file is invalid (non-Microsoft Win32® .exe or error in .exe image).
SE_ERR_ACCESSDENIED - The operating system denied access to the specified file.
SE_ERR_ASSOCINCOMPLETE - The file name association is incomplete or invalid.
SE_ERR_DDEBUSY - The Dynamic Data Exchange (DDE) transaction could not be completed because other DDE transactions were being processed.
SE_ERR_DDEFAIL - The DDE transaction failed.
SE_ERR_DDETIMEOUT - The DDE transaction could not be completed because the request timed out.
SE_ERR_DLLNOTFOUND - The specified dynamic-link library (DLL) was not found.
SE_ERR_FNF - The specified file was not found.
SE_ERR_NOASSOC - There is no application associated with the given file name extension. This error will also be returned if you attempt to print a file that is not printable.
SE_ERR_OOM - There was not enough memory to complete the operation.
SE_ERR_PNF - The specified path was not found.
SE_ERR_SHARE - A sharing violation occurred.

************************************************************************************

Good Luck,

Jared
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Author Comment

by:shanncan
ID: 10854181

Thanks for your replies folks.

AlexFM - can you further explain your answer on the locking aspect. I understand what you mean when you say that it depends on the program whether the file is locked or not. But - it is essential that the file is locked when the associated program opens it. Can I force the file to be locked in someway?

    You said that text editors like notepad dont lock files all the time that they are opened - just when the file is loaded or unloaded ..... What does this mean? Does it mean that notepad locks the file as it opens the file and then removes the lock - and then when it goes to close the file it locks the file again and unlocks it when it drops the file handle? I dont understand this....
    Is there anyway that I can find out if the file is most definitely locked? Or even get a list of all the associated programs that can carry out the locking?

   I have been trying to open files in their associated program like this ....

call ShellExecuteA (0, "Open", cur_path, "Lock Read Write", vbNullString, 1)

  where the variable "cur_path" would contain the file name.
 
  i need to ensure that the file is locked. Am I doing it right for the programs that do lock files?

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Expert Comment

by:Melih SARICA
ID: 10854249
Locking a file in not about the execution method..

Its about the Application that ur using it to open..

If the application that opens the file, locked the file while openning it ll be locked.. No other way to lock it..

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LVL 48

Expert Comment

by:AlexFM
ID: 10857021
Try to open file in Notepad - after it is opened, you can delete it in Explorer. After file is opened, Notepad keeps it in memory and doesn't lock file itself.
Try to do the same with Word - you cannot. Word locks the file all time it is opened.
I don't think you can force another program to lock the file.
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