Quite a frequent problem when working with signals with slots in Qt5, according to my observations on the forum, is the connection of slots in the syntax on the pointers to signals having an overload of the signature. The same applies to slots that have an overload.
Let's take a test class that has overloaded signals.
- The signal/slot mechanism is a central feature of Qt and probably the part that differs most from other toolkits. In most GUI toolkits widgets have a callback for each action they can trigger. This callback is a pointer to a function. In Qt, signals and slots have taken over from these messy function pointers.
- A developer can choose to connect to a signal by creating a function (a slot) and calling the connect function to relate the signal to the slot. Qt's signals and slots mechanism does not require classes to have knowledge of each other, which makes it much easier to develop highly reusable classes.
Here there is a signal, with an overload of the signature. Connect this signal will also be to the slots that are declared in the Widget class, and which also have an overload of the signature.
Boost and QT also offer signal / slot functionality (see Part 1 of the article series). However, the signal slot system by ElmueSoft described in this article has the great advantage that it is tiny, does not need any big libraries or compiler plugins and it is free! You will not want to miss it if you once got used to it! I'm using Qt Creator 2.0.1 and I have a custom slot my QMainWindow. Now I have a pushbutton, which on clicked should call the custom slot on the main window. Can do in code yes, but can't do this with the signal-slot editor. When I open the signal-slot editor, I see the custom slot on the right but the entire set of slots are disabled.
Qt Signal Slot Example C
How it was in Qt4
Within Qt4, everything was solved quite simply by specifying the signature of the signal and the slot in the SIGNAL and SLOT macros.
How it became in Qt5
But in Qt5, when writing in the new syntax of signals and slots, there are some problems. Because you need to make the static_cast of the method signature.
Signal Slot Qt C++ Free
By the way, the new syntax also allows you to connect signals to slots with a smaller signature, as it was in Qt4.
Advantages of the new syntax
Signal Slot Qt C++ Programming
Signal Slot Qt With Param
And now a stumbling block. Why use the new syntax of signals and slots? I still hear this question from time to time. Especially when people see such terrible castes of signatures.
Quite a frequent problem when working with signals with slots in Qt5, according to my observations on the forum, is the connection of slots in the syntax on the pointers to signals having an overload of the signature. The same applies to slots that have an overload.
Let's take a test class that has overloaded signals.
- The signal/slot mechanism is a central feature of Qt and probably the part that differs most from other toolkits. In most GUI toolkits widgets have a callback for each action they can trigger. This callback is a pointer to a function. In Qt, signals and slots have taken over from these messy function pointers.
- A developer can choose to connect to a signal by creating a function (a slot) and calling the connect function to relate the signal to the slot. Qt's signals and slots mechanism does not require classes to have knowledge of each other, which makes it much easier to develop highly reusable classes.
Here there is a signal, with an overload of the signature. Connect this signal will also be to the slots that are declared in the Widget class, and which also have an overload of the signature.
Boost and QT also offer signal / slot functionality (see Part 1 of the article series). However, the signal slot system by ElmueSoft described in this article has the great advantage that it is tiny, does not need any big libraries or compiler plugins and it is free! You will not want to miss it if you once got used to it! I'm using Qt Creator 2.0.1 and I have a custom slot my QMainWindow. Now I have a pushbutton, which on clicked should call the custom slot on the main window. Can do in code yes, but can't do this with the signal-slot editor. When I open the signal-slot editor, I see the custom slot on the right but the entire set of slots are disabled.
Qt Signal Slot Example C
How it was in Qt4
Within Qt4, everything was solved quite simply by specifying the signature of the signal and the slot in the SIGNAL and SLOT macros.
How it became in Qt5
But in Qt5, when writing in the new syntax of signals and slots, there are some problems. Because you need to make the static_cast of the method signature.
Signal Slot Qt C++ Free
By the way, the new syntax also allows you to connect signals to slots with a smaller signature, as it was in Qt4.
Advantages of the new syntax
Signal Slot Qt C++ Programming
Signal Slot Qt With Param
And now a stumbling block. Why use the new syntax of signals and slots? I still hear this question from time to time. Especially when people see such terrible castes of signatures.
- Therefore, I will list potential advantages:The ability to track errors in the connection of signals and slots at the compilation stage, rather than in the runtime
- Reducing compilation time by excluding macros from the code
- The ability to connect lambda functions, it's quite an important bun
- We protect ourselves from errors when we try to connect from the outside to a private slot. Yes!! Yes!! The SIGNAL and SLOT macros ignore the access levels of methods, violating OOP.
Signal Slot Qt C++ Tutorial
In general, for me this is enough, but for you?
