Signals and slots is a language construct introduced in Qt for communication between objects[1] which makes it easy to implement the observer pattern while avoiding boilerplate code. The concept is that GUI widgets can send signals containing event information which can be received by other widgets / controls using special functions known as slots. This is similar to C/C++ function pointers, but signal/slot system ensures the type-correctness of callback arguments.[citation needed]
![Boost Boost](https://programmer.help/images/blog/be96a1f16a64c4c0368a2d1db1df8ac3.jpg)
The signal/slot system fits well with the way graphical user interfaces are designed. Similarly, the signal/slot system can be used for other non-GUI usages, for example asynchronous I/O (including sockets, pipes, serial devices, etc.) event notification or to associate timeout events with appropriate object instances and methods or functions. It is easy to use and no registration/deregistration/invocation code need to be written, because Qt's metaobject compiler (MOC) automatically generates the needed infrastructure.
A commonly used metaphor is a spreadsheet. A spreadsheet has cells that observe the source cell(s). When the source cell is changed, the dependent cells are updated from the event.
A Deeper Look at Signals and Slots ScottCollins2005.12.19 what are signals and slots? # showing how to mix Qt Signals and Slots with Boost.Signals # # Things you'll have in your.pro when you try this. # CONFIG += nokeywords # so Qt won't #define any non-all-caps `keywords'.
- Then to continue using Qt signals and slots with the nokeywords flag, simply replace all uses of the Qt moc keywords in your sources with the corresponding Qt macros QSIGNALS (or QSIGNAL), QSLOTS (or QSLOT), and QEMIT. There is a complete explanation of how to connect boost signals to qt signals.
- Messaging and Signaling in C. Published at 15:28 by Jens Weller. This is the 7th blog post in my series about writing applications with C using Qt and boost.This time it is about how to notify one part of our application that something has happened somewhere else.
Alternative implementations[edit]
![Qt signal slot example Qt signal slot example](https://i.ytimg.com/vi/P_uYKl5RPTk/maxresdefault.jpg)
There are some implementations of signal/slot systems based on C++ templates, which don't require the extra metaobject compiler, as used by Qt, such as libsigc++, sigslot, vdk-signals, nano-signal-slot, neosigslot, Signals, boost.signals2, Synapse, Cpp::Events, Platinum and JBroadcaster. Common Language Infrastructure (CLI) languages such as C# also supports a similar construct although with a different terminology and syntax: events play the role of signals, and delegates are the slots. Another implementation of signals exists for ActionScript 3.0, inspired by C# events and signals/slots in Qt. Additionally, a delegate can be a local variable, much like a function pointer, while a slot in Qt must be a class member declared as such. The C based GObject system also provides similar functionality via GSignal.In D it is implemented by std.signals.
See also[edit]
Libraries[edit]
Boost Signal Slot Vs Qt 3
Java: sig4j - multi-threaded, type-safe, based on the FunctionalInterface annotation introduced in Java 8.
C++: vdk-signals - thread-safe, type-safe, written in C++11 with atomic variables.
References[edit]
- ^'Signals & Slots - QtCore 5.1'. Qt Project. 2013-07-04. Retrieved 2013-07-04.
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Signals_and_slots&oldid=839724350'
Join GitHub today
GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.
Join the fun at Santa Ana Star, the best casino in New Mexico! Located in Santa Ana, NM offering Gaming, Bowling, Golf, Dining, Hotel, and More. Gaming Get Lucky! Casino Gaming at the Santa Ana Star. Santa Ana Star Casino Hotel has over 1,600 of the loosest slot machines in New Mexico and the most exciting table games, which means you can choose your way to win! Santa ana casino poker room. The Santa Ana Star Casino is located in Bernalillo, a small city between Albuquerque and Santa Fe, just west of Interstate 25. It is a full service New Mexican casino, located on an Indian pueblo. Oct 30, 2019 Information and Reviews about Santa Ana Star Poker Room in Bernalillo, including Poker Tournaments, Games, Special Events and Promotions. ALL-New 14 Table Poker Room Visit Santa Fe's new live poker room. Contact Information. Santa Fe Station 4949 N Rancho Dr Las Vegas, NV 89130 Distance from Airport: 19 mile Hotel Reservations: 702-658-4900. View Larger Map. Casino, Hotel, Parking, Restaurants, Health and Beauty Spa.
Sign upHave a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
Milestone
Comments
commented Jun 16, 2015
Compiling a rqt_gui_cpp plugin which (transitively) depends on boost signals (e.g. via tf package) fails to compile due to macro name clashes of Qt's 'signals', 'slots', 'emit' macros as described here: http://wiki.ros.org/qt_ros/Tutorials/Mixing%20Qt%20and%20Boost%20Signals For such a plugin to compile the QT_NO_KEYWORDS flag can be set in its cmake file: ADD_DEFINITIONS(-DQT_NO_KEYWORDS) But this breaks the current code of qt_gui_core at: https://github.com/ros-visualization/qt_gui_core/blob/fuerte-devel/qt_gui_cpp/include/qt_gui_cpp/plugin_bridge.h#L63 And also a few other files in the rqt package are affected: https://github.com/ros-visualization/rqt/search?l=cpp&q=signals+OR+slots+OR+emit&type=Code&utf8=%E2%9C%93 Changing the keywords as follows would resolve this issue:
The use of the QT_NO_KEYWORDS flag should also be mentioned in the rqt cpp plugin tutorial. |
Qt Signal Slot Queue
Sign up for freeto join this conversation on GitHub. Already have an account? Sign in to comment