Obtains the Windows handle of a PocketBuilder object. You can get the handle of the application, a window, or a control, but not a drawing object.
Handle ( objectname {, previous } )
Argument |
Description |
|---|---|
objectname |
The name of the object for which you want the handle. Objectname can be any PocketBuilder object, including an application or control, but cannot be a drawing object. |
previous (optional) |
(Obsolete argument) A boolean indicating whether you want the handle of the previous instance of an application. You can use this argument with the Application object only. In current versions of Windows, Handle always returns 0 when this argument is set to true. |
Long. Returns the handle of objectname. If objectname is an application and previous is true, Handle always returns 0.
If objectname cannot be referenced at runtime, Handle returns 0 (for example, if objectname is a window and is not open).
Use Handle when you need an object handle as an argument to Windows Software Development Kit (SDK) functions or the PowerScript Send function.
Use IsValid instead of the Handle function to determine whether a window is open.
When you ask for the handle of the application, Handle returns 0 when you are using the PowerScript Run command. As far as Windows is concerned, your application does not have a handle when it is run from PocketBuilder. When you build and run an executable version of your application, the Handle function returns a valid handle for the application.
If you ask for the handle of a previous instance of an application by setting the previous flag to true, Handle always returns 0 in current versions of Windows. Use the Windows FindWindow function to determine whether an instance of the application’s main window is already open.
This statement returns the handle to the window w_child:
Handle(w_child)
These statements use an external function called FlashWindow to change the title bar of a window to inactive and then return it to active. The external function declaration is:
function boolean flashwindow(uint hnd, boolean inst) & library "user.exe"
The code that flashes the window’s title bar is:
integer nLoop // Loop counter long hWnd // Handle to control // Get the handle to a PowerBuilder window. hWnd = Handle(Parent) // Make the title bar flash 300 times. FOR nLoop = 1 to 300 FlashWindow (hWnd, true) NEXT // Return the window to its original state. FlashWindow (hWnd, FALSE)
For applications, the Handle function does not return a useful value when the previous flag is true. You can use the FindWindow Windows function to determine whether a Windows application is already running. FindWindow returns the handle of a window with a given title.
Declare FindWindowA and SetForegroundWindow as global external functions:
PUBLIC FUNCTION unsignedlong FindWindow (long & classname, string windowname) & LIBRARY "user32.dll" ALIAS FOR FindWindowA
PUBLIC FUNCTION int FindWindowA (long classname, & string windowname) LIBRARY "user32.dll"
PocketBuilder applications
In PocketBuilder, you would declare two versions of each function,
for use in testing on the desktop and in the deployed application:
public FUNCTION unsignedlong FindWindow_NT( long & ClassName, string WindowName ) & LIBRARY "user32.dll" ALIAS FOR "FindWindowW" public FUNCTION unsignedlong FindWindow_CE( long & ClassName, string WindowName ) & LIBRARY "coredll.dll" ALIAS FOR "FindWindowW" public FUNCTION int SetForegroundWindow_NT( & unsignedlong hwnd ) LIBRARY "user32.dll" & ALIAS FOR "SetForegroundWindow" public FUNCTION int SetForegroundWindow_CE( & unsignedlong hwnd ) LIBRARY "coredll.dll" & ALIAS FOR "SetForegroundWindow"
Then add code like the following to your application’s Open event:
unsignedlong hwnd hwnd = FindWindow( 0, "Main Window") if hwnd = 0 then // no previous instance, so open the main window open( w_main ) else // open the previous instance window and halt SetForegroundWindow( hwnd ) HALT CLOSE end if
