Run only one instance of your application: Difference between revisions

Run only one instance of your application (view source)

Revision as of 00:14, 11 December 2007

16 bytes added , 11 December 2007

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Hellboy1975

221

edits

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 The question on how to make sure that your application is only started once by your users can be approached in several ways.
-. Using mutexes
+# Using mutexes
-. Using FindWindow WinAPI
+# Using FindWindow WinAPI
 === Using mutexes ===
@@ Line 11: / Line 11: @@
 In the SRC file within the panel object put this piece of code:
- Procedure Exit_Application
+<pre>
+Procedure Exit_Application
      integer iVoid
      If (ghMuteX) Move (CloseHandle(ghMutex)) to iVoid
      move 0 to ghMuteX
      Forward Send Exit_Application
- End_Procedure
+End_Procedure
+</pre>
 And in a package that gets hit on startup:
- // Constants
+<pre>
- Define ERROR_INVALID_HANDLE        for 6    //  taken from error.h of VS7
+// Constants
- Define ERROR_ALREADY_EXISTS        for 183<br/>
+Define ERROR_INVALID_HANDLE        for 6    //  taken from error.h of VS7
- Handle ghMuteX<br/>
+Define ERROR_ALREADY_EXISTS        for 183<br/>
- // external functions
+Handle ghMuteX<br/>
- #IFNDEF Get_CreateMuteX
+// external functions
-     External_Function CreateMuteX "CreateMutexA" Kernel32.dll Integer i1 Integer i2 Integer i3 Returns Integer
+#IFNDEF Get_CreateMuteX
- #ENDIF
+    External_Function CreateMuteX "CreateMutexA" Kernel32.dll Integer i1 Integer i2 Integer i3 Returns Integer
- #IFNDEF Get_CloseHandle
+#ENDIF
-    External_Function CloseHandle "CloseHandle" Kernel32.dll Integer i1 Returns Integer
+#IFNDEF Get_CloseHandle
- #ENDIF<br/>
+   External_Function CloseHandle "CloseHandle" Kernel32.dll Integer i1 Returns Integer
- // function to create a mutex
+#ENDIF<br/>
- Procedure Create_MuteX_Object
+// function to create a mutex
-    Integer iVoid iErr
+Procedure Create_MuteX_Object
-    String sID
+   Integer iVoid iErr
-    Move "Unique String For My Application" To sID
+   String sID
-    Move (CreateMuteX(0,1,AddressOf(sID))) To ghMuteX
+   Move "Unique String For My Application" To sID
-    If (ghMuteX <> ERROR_INVALID_HANDLE) Begin
+   Move (CreateMuteX(0,1,AddressOf(sID))) To ghMuteX
-        Move (GetLastError()) To iErr
+   If (ghMuteX <> ERROR_INVALID_HANDLE) Begin
-        If (iErr = ERROR_ALREADY_EXISTS) Begin  // program is already
+       Move (GetLastError()) To iErr
-                                                // running
+       If (iErr = ERROR_ALREADY_EXISTS) Begin  // program is already
-            Move (CloseHandle(ghMuteX)) To iVoid
+                                               // running
-            Move 0 To ghMuteX
+           Move (CloseHandle(ghMuteX)) To iVoid
-            // kill the application here if you do not want to allow
+           Move 0 To ghMuteX
-            // multiple instances
+           // kill the application here if you do not want to allow
-            ABORT
+           // multiple instances
-        End
+           ABORT
-        Else Send None  // program is not already running
+       End
-    End
+       Else Send None  // program is not already running
-    Else Send None  // rare error; object could not be created
+   End
- End_Procedure  // Create_MuteX_Object<br/>
+   Else Send None  // rare error; object could not be created
- // create the mutex
+End_Procedure  // Create_MuteX_Object<br/>
- Send Create_MuteX_Object
+// create the mutex
+Send Create_MuteX_Object
+</pre>
 === Using FindWindow WinAPI ===
@@ Line 57: / Line 61: @@
 Usage in SRC:
+<pre>
   Use myPanel,pkg
   Object Main is a myPanel
+</pre>
 Source myPanel.pkg
+<pre>
   ////////////////////////////////////////////
   //
@@ Line 99: / Line 104: @@
        End_Procedure // End_Construct_Object
   End_class
+</pre>
 The FindWindow technique is also discussed in the book [http://www.starzen.com/Products/DataFlexVDF/Books/tabid/56/Default.aspx Mastering Visual DataFlex] from Starzen.
-[[Category: How To]]
+[[Category: Tutorials]]