On Sunday, 18 February 2018 20:59:50 PST Tom Isaacson via Interest wrote:
> I'm replacing some old SIGNAL/SLOT connects with the new Qt5 format and I
> need to use lambdas for some of them.
>
> Scenario 1:
>
> public slots:
> void RouteEditName();
> void RouteEditName(QString name);
>
> m_pRouteEditNameAct = new tAction(tr("Name route") + "...", this);
> connect(m_pRouteEditNameAct, SIGNAL(triggered()), this,
> SLOT(RouteEditName()), Qt::QueuedConnection);
>
> If someone has been naughty and overloaded a slot then normally I'd just use
> a lambda to indicate which slot is being called:
> connect(m_pRouteEditNameAct, this, &tAction::triggered, [this]() {
> RouteEditName(); });
Make this a four-argument connect.
> But in this case I need to add Qt::QueuedConnection but connect() won't take
> four params like this: connect(m_pRouteEditNameAct, this,
> &tAction::triggered, [this]() { RouteEditName(); }, Qt::QueuedConnection);
Make this one a five-argument connect().
> Do I just add an unnecessary 'this' to fill it out?
> connect(m_pRouteEditNameAct, this, &tAction::triggered, this, [this]() {
> RouteEditName(); }, Qt::QueuedConnection);
It's not unnecessary. It's good practice.
And in your case, absolutely necessary. You cannot queue a connection without
a target QObject to be queued to. THAT is what that extra "this" is for.
> Scenario 2:
>
> Later I need to disconnect this:
> disconnect(m_pRouteEditNameAct, SIGNAL(triggered()), this,
> SLOT(RouteEditName()));
>
> But how do I disconnect a lambda?
> disconnect(m_pRouteEditNameAct, &tAction::triggered, this, [this]() {
> RouteEditName(); });
disconnect() does not have such an overload. To disconnect anew-style connect,
you must pass the QMetaObject::Connection object that connect() returned.
--
Thiago Macieira - thiago.macieira (AT) intel.com
Software Architect - Intel Open Source Technology Center
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