The CS_SLOT() macro is only required if your application is going to look up the slot at run time, using a string. The CS_SIGNAL() and CS_SLOT() macros are used to declare and register the method names and parameters with the CopperSpice meta object system. The following example shows how to declare a class which contains a signal and a slot. There are multiple overloads and several which can be used to disconnect all existing connections which match certain criteria. The disconnect() method which breaks the signal / slot relationship. Signals and slot are often connected and disconnected multiple times in response to the user input. It can also connect multiple signals to a single slot. Using the connect() method, an application can connect a one given signal to multiple slots. All classes which inherit from QObject or one of its subclasses may contain signals and slots. A class which emits a signal does not need to know which slots receive the signal. The only constraint is that if the slot needs to receive some of the arguments the order must match those emitted by the signal. The slot can ignore any or all of these arguments. The signal can be designed to emit any number of parameters of any copyable data type. Syntax for a callback can be complicated to read or understand.Callbacks do not support lambda expressions which can capture local data.In a multithreaded application callbacks often cause race conditions.Invoking a callback is not usually type safe.A slot is the response which is usually a call to a method or function. A signal is emitted when a particular action occurs, such as the mouse click. The signal / slot mechanism in CopperSpice is type safe and works across threads. A slot is usually a method and will be called in response to the signal. In this paradigm a signal is emitted when a particular event occurs. Callbacks can have fundamental limitations and are not the best solution for a C++ GUI program.Ī more effective approach than callbacks is the mechanism provided by Signals and Slots. With callbacks, when something happens an event handler will use the callback pointer to invoke the callback function. Some programs or libraries accomplish this by using callbacks, which is a pointer to a function. In the case of the mouse click action the program should respond by closing the desired window. Since this is a common occurrence a GUI library should have a convenient mechanism to associate actions taken by the user to some process the program should take. If a user clicks a close button they probably want to close the corresponding window. A key aspect of a well designed GUI program involves responding to actions taken by the user of the software.

Qt one signal to multiple slots order