Delphi: Send message to running instance of same app, without any TForm

Question

I'd like to know a way to do the following:

App starts, no forms created. 2nd App instance starts, it detects one instance is already running (this is sorted already)

I want 2nd instance to send the 1st one a message, without using BROADCAST; Id like a way to find a handle to the 1st instance to send it the message directly.

The 1st instance must have a class name to be found with that the 2nd one hasn't yet created, so that it won't send the message to itself.

How would I use FindWindow in this scenario? How do I create a window-less class/object identifiable by FindWindow?

FindWindow finds a window by either class name or caption, so it can't find anything that is windowless. (That's why the function is called Find**Window**). It also returns a window handle - if it could find something that was windowless, what would it return? — Ken White
– Ken White, Commented Nov 11, 2012 at 3:43
Well I can create a "window" with AllocateHWnd, but then I don't know how to find it from the other instance. — hikari
– hikari, Commented Nov 11, 2012 at 3:47
Well, if you create a window with AllocateHWnd, it's not windowless, is it? And you specifically asked about using FindWindow to find a windowless application. "How di I create a window-less class/object identifiable by FindWindow?" were your exact words. — Ken White
– Ken White, Commented Nov 11, 2012 at 3:55
@KenWhite "windowless" in this context means no TForm instance, it is wrong, because not only TForm is a window. So every "windowless" should be replaced by "formless". There is no need of kicking ... — Sir Rufo
– Sir Rufo, Commented Nov 11, 2012 at 8:37

MBo · Accepted Answer · 2012-11-11 03:49:27Z

2

You can not find windowless object by means of FindWindow.

But you can create invisible window with AllocateHWnd function - see TTimer source as example. Use SetWindowText to set title for easy searching

answered Nov 11, 2012 at 3:49

MBo

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2 Comments

Ken White Over a year ago

If you create a windows using AllocateHWnd, then it's no longer windowless, and the question asked for windowless specifically.

MBo Over a year ago

Some people consider programs without visible windows as windowless, I think

Remy Lebeau · Accepted Answer · 2012-11-11 19:01:09Z

1

You can send messages to the TApplication window if you know the value of its Title property. The sending instance can temporarily set its own Title to a different value so as not to confuse FindWindow(). The receiving instance can use the TApplication.OnMessage event or TApplication.HookMainWindow() method to receive the message.

answered Nov 11, 2012 at 19:01

Remy Lebeau

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alzaimar · Accepted Answer · 2012-11-11 08:37:12Z

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You could use shared memory to pass data. See this article for details

answered Nov 11, 2012 at 8:37

alzaimar

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2 Comments

David Heffernan Over a year ago

Don't used shared memory. Send messages.

hikari Over a year ago

Using that already for other purposes, but in this case I wanna sort the issue with SendMessage

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