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An event requires an accompanied event handler that is made from a special delegate that in a platform specific library like in Windows Presentation Foundation and Windows Forms usually takes two parameters: sender and the event arguments. The type of the event argument-object derive from the EventArgs class that is a part of the CLI base library.
First, the async keyword indicates to C# that the method is asynchronous, meaning that it may use an arbitrary number of await expressions and will bind the result to a promise. [1]: 165–168 The return type, Task<T>, is C#'s analogue to the concept of a promise, and here is indicated to have a result value of type int.
C# (/ ˌ s iː ˈ ʃ ɑːr p / see SHARP) [b] is a general-purpose high-level programming language supporting multiple paradigms.C# encompasses static typing, [16]: 4 strong typing, lexically scoped, imperative, declarative, functional, generic, [16]: 22 object-oriented (class-based), and component-oriented programming disciplines.
CLI languages such as C# and VB.NET provide a type-safe encapsulating function reference known as delegate. Events and event handlers, as used in .NET languages, provide for callbacks. Functional languages generally support first-class functions, which can be passed as callbacks to other functions, stored as data or returned from functions.
In C#, delegates are often used to implement callbacks in event driven programming. For example, a delegate may be used to indicate which method should be called when the user clicks on some button. Delegates allow the programmer to notify several methods that an event has occurred.
Below is an example written in Java that takes keyboard input and handles each input line as an event. When a string is supplied from System.in , the method notifyObservers() is then called in order to notify all observers of the event's occurrence, in the form of an invocation of their update methods.
Additionally, in C# if a block consists of only a single statement, the braces may be omitted. C# is case sensitive while Visual Basic .NET is not. Thus in C# it is possible to have two variables with the same apparent name, for example variable1 and Variable1. Visual Studio will correct (make uniform) the case of variables as they are typed in ...
The actual logic is contained in event-handler routines. These routines handle the events to which the main program will respond. For example, a single left-button mouse-click on a command button in a GUI program may trigger a routine that will open another window, save data to a database or exit the application.