An event and event handler can be defined in one assembly, and consumed by another assembly. An event is a message sent by an object to signal the occurrence of an action. Allows derived classes to override the event behavior by using the. For more information, see Static Classes and Static Class Members. Events in.NET follow the observer design pattern. For more information and code examples, see Events and Delegates. This enables derived classes to override the event behavior by using the override keyword. Hooking Event Handlers to Events This article shows how to use an interface that declares an event and a function to invoke that event, and the class and event handler that implement the interface. This makes the event available to callers at any time, even if no instance of the class exists.

An event handler, in C#, is a method that contains the code that gets executed in response to a specific event that occurs in an application. These access modifiers define how users of the class can access the event. For the complete code example that also shows how to use the generic EventHandler delegate type and how to subscribe to an event and create an event handler method, see How to: Publish Events that Conform to .NET Framework Guidelines.Events are a special kind of multicast delegate that can only be invoked from within the class or struct … C# - Events An event is a notification sent by an object to signal the occurrence of an action. public delegate void MyEventHandler (object sender, MyEventArgs e); The first parameter (sender) in the above declaration specifies the object that fired the event. For more information, see Inheritance. How to: Use Events in C++/CLI. 11/04/2016; 8 minutes to read +2; In this article. You must define all of the event's accessor functions, and then specify the new or override keyword on each accessor function. The language specification is the definitive source for C# syntax and usage. Events are a special kind of multicast delegate that can only be invoked from within the class or struct where they are declared (the publisher class). To associate the event with the method that will handle the event, add an instance of the delegate to the event. Events can be marked as public, private, protected, internal, protected internal, or private protected. For more information, see the C# Language Specification. Event handlers are used in graphical user interface (GUI) applications to handle events such as button clicks and menu selections, raised by controls in the user interface. For more information, see Access Modifiers.

The following example shows how to declare and raise an event that uses EventHandler as the underlying delegate type. How to publish events that conform to .NET Guidelines, How to combine delegates (Multicast Delegates). The class who raises events is called Publisher, and the class who receives the notification is called Subscriber. Defining Event Handlers In an event receiver class, you define event handlers, which are methods with signatures (return types, calling conventions, and arguments) that match the event that they will handle. This sample implements virtual, managed events in an interface and class: A simple event cannot be specified to override or hide a base class event. Specifies that for derived classes it is no longer virtual.

Therefore derived classes must provide their own implementation. The event sender doesn't know which object or method will receive (handle) the events it raises. The event is typically a member of the event sender; for example, the Click event is a member of … For the complete code example that also shows how to use the generic EventHandler delegate type and how to subscribe to an event and create an event handler method, see How to publish events that conform to .NET Guidelines. The object that raises the event is called the event sender. VS.NET generates the handler methodnames by using the fieldname of the sender object (the name of the variable sending events), and concatenate's to it an underscore followed by the name of the event. The following code example adds an event handler, invokes the event—which causes the event handler to write its name to the console—and then removes the event handler. The event keyword is used to declare an event in a publisher class. An event can be marked as a virtual event by using the virtual keyword. This article shows how to use an interface that declares an event and a function to invoke that event, and the class and event handler that implement the interface. The second parameter (e) of the above declaration holds data that can be used in the event handler. The following example shows how to declare and raise an event that uses EventHandler as the underlying delegate type. Lastly, an event can be declared abstract, which means that the compiler will not generate the add and remove event accessor blocks. Makes the event available to callers at any time, even if no instance of the class exists. An event may be declared as a static event by using the static keyword. For more information about event handler delegates, see Handling and Raising Events. The action can be caused by user interaction, such as a button click, or it can result from some other program logic, such as changing a property’s value. The following sample shows how to define an event's behavior when handlers are added or removed, and when an event is raised. The following sample shows how to define and use static events. The event handler is called whenever the event occurs, unless you remove the delegate.

The following sample shows how to implement an abstract event. It is good practice to follow this convention whenever you are handling events of objects that are declared as fields on your class.