Weird issue with SIGNAL/SLOT

[leinad]

@JonB Sorry. I fixed using the back tics. Can you explain how I can connect a lambda to the signal?

[Atr0p0s]

@leinad Here is a good explanation.

[JonB]

@leinad
That's much more readable, thank you :)

I didn't want to bring this up, because it likely has nothing to do with your issue, but SIGNAL/SLOT() macros are the old style of Qt connect()s. Unfortunately a lot of examples on the web still use them. The new style was introduced a decade ago as C++ supported it. It is type-safe and gives compile time errors if the slot is not right for the signal.

connect(signalObject, &SignalClass::method, slotObject, &SlotClass::method);

So for your connect(selectdatabase_, SIGNAL(sendDatabaseName(QString)), databaseProcessing_, SLOT(getDatabaseName(QString)));:

connect(selectdatabase_, &SelectDatabase::sendDatabaseName, databaseProcessing_, &DatabaseProcessing::getDatabaseName);

Doesn't that look tidier? :) I really suggest you change to this syntax from now onwards.

You need new-style to use C++ lambdas for the slot. I suggest you try something like:

connect(selectdatabase_, &SelectDatabase::sendDatabaseName,
        databaseProcessing_, [](QString databaseName) { qDebug() << "sendDatabaseName" << databaseName; } );

Now we know whether signal is emitted and passes database name. Does this work?

[leinad]

@JonB
Thanks, I see. I will give it a try.

[leinad]

@JonB said in Weird issue with SIGNAL/SLOT:

connect(signalObject, &SignalClass::method, slotObject, &SlotClass::method);

Funny, I use QtCreator with TIDY and it never called it out as a bad style. Perhaps the default options disable it?

[leinad]

@JonB

connect(selectdatabase_, &SelectDatabase::sendDatabaseName,
        databaseProcessing_, [](QString databaseName) { qDebug() << "sendDatabaseName" << databaseName; } );

I'm afraid I can't use this lambda function because I don't have access to databaseName, it is a QString which is sent from another object outside of the connect class.

[leinad]

@JonB
Sorry never mind. I can indeed use it.

[leinad]

@leinad
So it appears that the lambda does indeed show the correct value passed but yet the SLOT does not show it :(

[JonB]

@leinad
This was just the first step. Now we know the signal does get emitted and the connect() attaches to it.

Now:

connect(selectdatabase_, &SelectDatabase::sendDatabaseName, databaseProcessing_, &DatabaseProcessing::getDatabaseName)

(Put a qDebug() << databaseName; as first statement in slot.) I presume you will say the slot does not get called?

If not, are selectdatabase_ and databaseProcessing_ in different threads? If so, do you allow the event loop to run (signals across threads are queued)?

[leinad]

@JonB
I figured out what is happening. Seems the Emit is being called before the connect statement had a chance to be called. I'll have to rearrange how statements get executed.

Thanks!