What does selector mean in objective c

When the user clicks the button or uses the keyboard shortcut , the NSButtonCell object sends a message instructing the application to do something. To do this, an NSButtonCell object must be initialized not just with an image, a size, and a label, but with directions on what message to send and who to send it to. Accordingly, an NSButtonCell instance can be initialized for an action message the method selector it should use in the message it sends and a target the object that should receive the message.

When the user clicks the corresponding button, the button cell sends the message using the NSObject protocol method performSelector:withObject:.

All action messages take a single parameter, the id of the control device sending the message. Instead of simply implementing a mechanism for translating user actions into action messages, button cells and other controls would have to constrain the content of the message.

Constrained messaging would make it difficult for any object to respond to more than one button cell. There would either have to be one target for each button, or the target object would have to discover which button the message came from and act accordingly. Each time you rearranged the user interface, you would also have to reimplement the method that responds to the action message. An absence of dynamic messaging would create an unnecessary complication that Objective-C happily avoids.

As you write your programs, you can make sure that the receiver is able to respond. If the receiver is statically typed, the compiler performs this test for you. However, if the message selector or the class of the receiver varies, it may be necessary to postpone this test until runtime.

The respondsToSelector: method, defined in the NSObject class, tests whether a receiver can respond to a message. So 1L equals 0. To calculate button size in ligne, simply divide the diameter of the button in millimeters by 0. The bottom buttonhole, along with the top button at the collar, are usually sewn horizontally to allow the button to take more stress from pulling and movement without stretching out the shirt or the hole itself.

It also, though, refers to the unique identifier that replaces the name when the source code is compiled. Compiled selectors are of type SEL.

An object that represents a special condition that interrupts the normal flow of program execution. Swift version: 5. Selectors are effectively the names of methods on an object or struct, and they are used to execute some code at runtime. A selector is the name used to select a method to execute for an object, or the unique identifier that replaces the name when the source code is compiled.

The only thing that makes the selector method name different from a plain string is that the compiler makes sure that selectors are unique. About Objective-C. And B use this selector to register notification. If I move all what I want to do in class B into class A, it worked. The core attributes of an NSError object are an error domain represented by a string , a domain-specific error code and a user info dictionary containing application specific information. NSException IntPtr A constructor used when creating managed representations of unmanaged objects; Called by the runtime.

The only thing which is important right now is that we use selectors to access the ID for a method. The reason why the internal ID is not important is that it might change with the new OS release. The concept is simple: when we have an object with some instance variables, KVO allows other objects to establish surveillance on changes for any of those instance variables.

KVO stands for Key-Value Observing and allows a controller or class to observe changes to a property value. In these cases, the SEL type can be used to hold a reference to the selector. The getter method is just name. Dynamic binding is determining the method to invoke at runtime instead of at compile time. Dynamic binding is also referred to as late binding.

In Objective-C, all methods are resolved dynamically at runtime. The exact code executed is determined by both the method name the selector and the receiving object. Static variables are those variables whose values are shared among all the instance or object of a class.

When we define any variable as static, it gets attached to a class rather than an object.