[Qt-interest] Forcing a signal "emit" to be queued

[Andre Somers]

Op 21-3-2011 7:30, Mandeep Sandhu schreef:
> Hi All,
>
> Sometime back I had a requirement where I didn't want ppl using my
> class's signals to connect to them directly. Currently if you do 'emit
> mySignal()', it's upto to the class that uses this signal, to decide
> how it would like to connect to it.
>
> For forcing a queued a connection, I thought of the following approach:
>
> connect(this, SIGNAL(myInternalSignal(), this, SIGNAL(mySignal()),
> Qt::QueuedConnection);
>
> Basically I'm chaining my signal and re-emitting it with the queued
> connection type (I've yet to verify this code though).
>
> How can one verify if the slot is indeed called in a queued connection?
Seems like a way to force preventing a direct connection, yes. However, 
please be aware that there are no private signals. Every signal is 
public. What's more, there is no access control on slots either. If you 
really want your signal to be private, then you need to emit it from a 
private internal class.

To verify if your pattern works, a simple debug session would suffice. 
Just put a breakpoint at the emit and start stepping though the code, 
or, if you want, put a breakpoint in the connected slot, and check the 
stack trace. A direct connected slot will have the class that emitted 
the signal in the stack, a queued connection will have the eventloop as 
the source of the call.

André