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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.
In object-oriented design, the chain-of-responsibility pattern is a behavioral design pattern consisting of a source of command objects and a series of processing objects. [1] Each processing object contains logic that defines the types of command objects that it can handle; the rest are passed to the next processing object in the chain.
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.
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.
In software engineering, a software design pattern or design pattern is a general, reusable solution to a commonly occurring problem in many contexts in software design. [1] A design pattern is not a rigid structure that can be transplanted directly into source code .
In the following example, a Mediator object controls the values of several Storage objects, forcing the user code to access the stored values through the mediator. When a storage object wants to emit an event indicating that its value has changed, it also goes back to the mediator object (via the method notifyObservers ) that controls the list ...
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.
The Bridge design pattern is one of the twenty-three well-known GoF design patterns that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse.