November 30, 2011

PEspie PEspie
Lab Rat
1 posts

[SOLVED] Cross-process UI interactions (Qt 4.8, Windows)

 

Hi All,

I’m quite new on Qt platform, sorry if I ask for some trivial questions (you can kick me to HOWTO if I’ve missed some ;)

I need to create a system to permit the creation of plug-in in our application, which is obviously written with Qt.
The requirement are simple:

  • Plug-in should live in another process (for security/stability reasons)
  • Plug-in should have access to at least a QWidget (I guess that behind, it will be a class derived from QWidget) to plys with (add it own widgets, draw inside, etc.)

On other words, I would need a kind of screen server (in my app) and a screen client (in my plug-in). The last one should be perfectly transparent for the plug-in.

There is an old demonstration wrote by “Marius” (I guess a kind of Qt God?) which do exactly what I need here: A Lighthouse with Windows [labs.qt.nokia.com] but the code is quite old (2010/02) and does not compile at all on Qt 4.8 version.

It seems that all this is working on Linux, but I can’t choose the platform: it’s Windows.

Any suggestion are welcome!

Thanks a lot
PEspie

4 replies

December 9, 2011

rcari rcari
Lab Rat
161 posts

Because you need to isolate the plugin in another process you’ll have to deal with Inter Process Communication (IPC).
On Windows there are two ways of doing this with Qt: shared memory and sockets. Shared memory can work but it’s usually overkill to implement or maintain… You should maybe look at TCP/IP and design some sort of client/server protocol for the plugin to interact with your main application.

Otherwise, I think you can use Windows native SendMessage/PostMessage to do some remote calls across processes given a window handle.

December 9, 2011

rcari rcari
Lab Rat
161 posts

Another option could be to create the child process using QProcess and use stdin/stdout streams to communicate with it. Some more protocol needed :)

December 12, 2011

PEspie PEspie
Lab Rat
1 posts

Thanks for your answer.

We finally choose to use some IPC for communication between processes, but the real challenge was the display … how to display from a process into another process window ?

This was solved by using, on Windows platform, the API function ::SetParent which permit to attach a window as a child of another window. This works across process boundary, so our problem is solved.

Once again, thanks!

July 12, 2013

francois francois
Lab Rat
2 posts

Pespie,

I have to execute a QWidget (in fact a QAxWidget) into an other process to protect my application from ActiveX crashes.

If I understand well, you used the SetParent() function to attach two widgets running in two different processes and then created an IPC protocol to handle signals, slots, method calls, etc… Am I right ?

Thanks

 
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