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A Windows Forms application is an event-driven application supported by Microsoft's .NET Framework. Unlike a batch program, it spends most of its time simply waiting for the user to do something, such as fill in a text box or click a button. The code for the application can be written in a .NET programming language such as C# or Visual Basic.
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.
Other implementations put command/event objects in other event objects (like a box inside a bigger box) as they move along the line, to avoid naming conflicts. (See also chain of responsibility pattern.) Handler, ExecutedRoutedEventHandler, method, function: the actual code that does the copying, pasting, moving, etc. In some implementations ...
In addition to writing the event handlers, event handlers also need to be bound to events so that the correct function is called when the event takes place. For UI events, many IDEs combine the two steps: double-click on a button, and the editor creates an (empty) event handler associated with the user clicking the button and opens a text ...
The observer design pattern is a behavioural pattern listed among the 23 well-known "Gang of Four" design patterns that address recurring design challenges in order to design flexible and reusable object-oriented software, yielding objects that are easier to implement, change, test and reuse.
Async methods that return void are intended for event handlers; in most cases where a synchronous method would return void, returning Task instead is recommended, as it allows for more intuitive exception handling. [18] Methods that make use of await must be declared with the async keyword.
Event propagation models, such as bubbling, capturing, and pub/sub, define how events are distributed and handled within a system. Other key aspects include event loops, event queueing and prioritization, event sourcing, and complex event processing patterns. These mechanisms contribute to the flexibility and scalability of event-driven systems.
Instead, Sender refers to the Handler interface for handling a request (handler.handleRequest()), which makes the Sender independent of which receiver handles the request. The Receiver1, Receiver2, and Receiver3 classes implement the Handler interface by either handling or forwarding a request (depending on run-time conditions).