Qt signal slot with return value
The signal must not use the Qt SIGNAL() macro; it should use the signal ... In this case, your slot should specify a compatible return type instead of void.
Signals & Slots | Qt Core 5.12.3 Signals and slots are loosely coupled: A class which emits a signal neither knows nor cares which slots receive the signal. Qt's signals and slots mechanism ensures that if you connect a signal to a slot, the slot will be called with the signal's parameters at the right time. Signals and slots can take any number of arguments of any type. Slot return value - what if it would be not lost? | Qt Forum Slot return value - what if it would be not lost? Slot return value - what if it would be not lost? ... I haven't run into a situation yet where the lack of return values from signals/slots have been a limiting factor. ... what people try to explain is that decoupling the emitter and the receiver of a signal is a fundamental principle of Qt ... Signals & Slots — Qt for Python An overview of Qt’s signals and slots inter-object communication mechanism. Signals and slots are used for communication between objects. The signals and slots mechanism is a central feature of Qt and probably the part that differs most from the features provided by other frameworks. How Qt Signals and Slots Work - Woboq
Boost.Signals allows various strategies of using the return values of slots to form the return value of the signal. E.g. adding them, forming a vector out of them, or returning the last one.. The common wisdom (expressed in the Qt documentation [EDIT: as well as some answers to this question ]) is that no such thing is possible with Qt signals.. However, when I run the moc on the following
The connection mechanism uses a vector indexed by signals. But all the slots waste space in the vector and there are usually more slots than signals in an object. So from Qt 4.6, a new internal signal index which only includes the signal index is used. While developing with Qt, you only need to know about the absolute method index. c++ - stack object Qt signal and parameter as reference - Stack Overflow - Stack Overflow … Qt::DirectionConnection. We can generally accept that this won't be a problem for direct connections as those slots are called immediately. Your signal emission blocks until all slots have been called. Once that happens, emit myQtSignal(fooStackObject); will return just like a regular function. In fact, myQtSignal(fooStackObject); is a regular How Qt Signals and Slots Work - Part 2 - Qt5 New Syntax
May 5, 2017 ... It is safe to connect signals and slots across different threads, thanks to ..... Note that the return value and return type of the map function are not ...
New Signal Slot Syntax - Qt Wiki Connecting in Qt 5. There are several ways to connect a signal in Qt 5. Old syntax. Qt 5 continues to support the old string-based syntax for connecting signals and slots defined in a QObject or any class that inherits from QObject (including QWidget) . connect( sender, SIGNAL( valueChanged( QString, QString ) ), receiver, SLOT( updateValue( QString ) ) ); c++ - Can Qt signals return a value? - Stack Overflow It captures the return value from the slot(s) invoked. Unfortunately, you only get the last return value. If you evaluate the code above, you'll get: "testSlot2", the last return value from the connected slots of the signal. Here's why. Qt Signals are a syntax sugared interface to the signaling pattern. Slots are the recipients of a signal. c++ - Qt: meaning of slot return value? - Stack Overflow the vector _a is a list of arguments that is passed to qt_metacall. This is passed by QMetaObject::invokeMethod. So the return value in the moc generated code is saved and passed back to the caller. So for normal signal-slot interactions the return value is not used for anything at all.
It captures the return value from the slot(s) invoked. Unfortunately, you only get the last return value. If you evaluate the code above, you'll get: "testSlot2", the last return value from the connected slots of the signal. Here's why. Qt Signals
Getting a return value from an emitted signal | Qt Forum Getting a return value from an emitted signal Getting a return value from an emitted signal ... If you need a return value, you'll need to revise your setup. ... Qt::DirectConnection 1 The slot is invoked immediately, when the signal is emitted.[/quote] This is true, but it's knowledge you should actually only use at the time you make the ... Signals & Slots | Qt Core 5.12.3 Signals and slots are loosely coupled: A class which emits a signal neither knows nor cares which slots receive the signal. Qt's signals and slots mechanism ensures that if you connect a signal to a slot, the slot will be called with the signal's parameters at the right time. Signals and slots can take any number of arguments of any type.
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