The `send-message-to-window` has a corresponding `on-message` method which
needs to be implemented in the target control for it to do something useful
so it is not a general replacement for `PostMessage`, but it can be used
for cases where PostMessage is called with WM_USER, messages.
The Windows `PostMessage` function is used for posting any message, and
windows GUI uses messages for everything. For example, to set the icon for
a toplevel window, one can send the WM_SETICON message as in:
PostMessage(aWindow, WM_SETICON, ICON_SMALL, anIcon)
The way to do hat in Racket is to call `set-icon`:
(send a-frame set-icon an-icon #f 'small)
However, the above call will have unexpected results if called from a
thread that is not the event handling thread: the correct way to make the
call from another thread is to use `queue-callback` like so:
(queue-callback (lambda () (send a-frame set-icon an-icon #f 'small))
I am not sure which methods on GUI classes are safe to be called from a
non-event handling thread, but most of them are not, so I use
`queue-callback` for all such cases. The PostMessage call works from any
thread, not just the event handling thread, so this problem does exist in
the Win32 API.
Alex.
On Tuesday, November 20, 2018 at 6:32:14 AM UTC+8, Philip McGrath wrote:
>
> There is a send-message-to-window function (
> http://docs.racket-lang.org/gui/Windowing_Functions.html#%28def._%28%28lib._mred%2Fmain..rkt%29._send-message-to-window%29%29),
>
> though I've never used it, and it sounds like it is different from what you
> describe.
>
> -Philip
>
>
> On Mon, Nov 19, 2018 at 5:22 PM Alex Harsanyi <alexha...@gmail.com
> <javascript:>> wrote:
>
>>
>>
>> I think `queue-callback` is the closest "general" equivalent: it allows
>> invoking methods on GUI objects from outside the event handler thread. It
>> can also be used to schedule some work to be done outside a GUI widget's
>> callback invocation.
>>
>> If you actually want to post specific messages to a window, you will have
>> to map "PostMessage" via FFI and you can find the target window handle
>> using `get-client-handle`. This will only work on the windows platform.
>>
>>
>> https://docs.racket-lang.org/gui/Windowing_Functions.html?q=ququq-callback#%28def._%28%28lib._mred%2Fmain..rkt%29._queue-callback%29%29
>>
>> Alex.
>>
>> On Monday, November 19, 2018 at 7:42:12 PM UTC+8, Jason Stewart wrote:
>>>
>>> In Windows, we have a SendMessage() function for dispatching a window
>>> event synchronously, and PostMessage() for asynchronously queuing an event
>>> to a specified window from any thread.
>>>
>>> Is there a way to do PostMessage() from Racket's GUI library?
>>>
>>> Eventspaces feels warm, but couldn't find what I was looking for in it:
>>>
>>>
>>> https://docs.racket-lang.org/gui/windowing-overview.html?q=sleep#%28part._eventspaceinfo%29
>>>
>>>
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