====== Flashing a Window ======

If a critical error condition occurs in a program, a visual cue such as flashing a window will more likely draw the user's attention to the problem.  This topic shows how to flash a window every 1/2 second, using the window's [[TIMER_event|TIMER event]] and the Windows API function [[https://msdn.microsoft.com/library/default.asp?url=/library/en-us/debug/base/flashwindow.asp|FlashWindow().]]  

=== The Code ===

In the window's [[TIMER_event|TIMER event]], code the following:

<code>
declare function FlashWindow

hwnd = Get_Property(@window , 'HANDLE')

invert = 1

fv = FlashWindow (hwnd, invert)
</code>
 

The code gets the window's [[HANDLE|HANDLE property]], and then passes it to [[https://msdn.microsoft.com/library/default.asp?url=/library/en-us/debug/base/flashwindow.asp|FlashWindow(),]] with the second argument (invert) indicating that the window should be flashed.

To start the flashing effect, simply start the timer by setting the [[TIMER|TIMER property]], passing the number of milliseconds between calling the [[TIMER_event|TIMER event]].   To flash the window every 1/2 second (500 milliseconds), code the following:

rv = Set_Property(@window , 'TIMER', 500)

To turn off the flashing, disable the call to the TIMER event by passing a 0, as shown below:

rv = Set_Property(@window , 'TIMER', 0)

=== The Windows API Declaration ===

The code above will not run until the declaration for [[https://msdn.microsoft.com/library/default.asp?url=/library/en-us/debug/base/flashwindow.asp|FlashWindow()]] has been added.  To add the declarations, do the following:

  * Log out of the application.
  * Log into the SYSPROG application.
  * Add a row, (call it DLL_APICALLS_USER32), with the first line as USER32 and containing the declaration as shown below.

<code>
USER32
ULONG STDCALL FlashWindow (ULONG, ULONG)
//....add any other declarations in USER32 here.....
</code>

  * Save  the row.
  * Run [[declare_FCNS|Declare_FCNS]] at the System Editor Exec Line to create the declaration header, as shown below:

RUN DECLARE_FCNS 'DLL_APICALLS_USER32'

  * Exit the editor.
  * Log out of SYSPROG.
  * Log into your application.
  * Run the window.