The calculator (Receiver) class is the main class used in the application to perform the commands. Here, the receiver object is the Document object. are the receivers. Maybe not all the posts will be much interesting, or interesting for many people, but still they will be useful for some. Definition: The command pattern encapsulates a request as an object, thereby letting us parameterize other objects with different requests, queue or log requests, and support undoable operations. Command pattern is an Object behavioral pattern that decouples sender and receiver by encapsulating a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undo-able operations. You might be able to use this to add “undo” capabilities to a program. Here you can see we have three commands. Command classes are usually limited to specific actions. Command pattern implementation Hi dear reader! The most important thing to remember while implementing the Command pattern is that the Command is just a link between the sender and receiver. In analogy to our problem above remote control is the client and stereo, lights etc. Receiver implementation is separate from command implementation. There are four parts to the Command pattern. Parts of the Command Design Pattern. Command pattern is a data driven design pattern and falls under behavioral pattern category. The most used implementation of the command pattern is the one used to implement the undo options in applications: Let's consider a calculator application. But actual implementation will be provided by different concrete classes where you will/can pass parameters (for example, via constructor). It can also be thought as an object oriented equivalent of call back method. Command pattern UML class diagram Using the code. In command pattern, typical command interface would have simple execute method - this can be represented by Action delegate. You can use the Command pattern to add work to a queue, to be done later. Implementation The idea is a table order at a restaurant: the waiter takes an order, which is the customer’s command.For the kitchen staff, this order is then queued. It should only tell the receiver what the sender is expecting. The Execute method will call the Open method of the Document object. Command . It has the request to open the document. Command is the core of command design pattern that defines the contract for implementation. The definition is a bit confusing at first but let’s step through it. Identification: The Command pattern is recognizable by behavioral methods in an abstract/interface type (sender) which invokes a method in an implementation of a different abstract/interface type (receiver) which has been encapsulated by the command implementation during its creation. As my PhD defense day had passed, I have a lot more time than some weeks ago, so I will be posting more often. Design-Patterns-in-C. Let’s see how to do a simple command pattern implementation by writing a small Dine & Chef application. Command Design Pattern Implementation using C#: Please have a look at the following image. Practical Design Patterns in C. This will be a repository of. It should never alter the logic of the sender and receiver in any way. The first one is the Open command. I have a similar implementation of Command Pattern in C#. Command implementation classes chose the method to invoke on receiver object, for every method in receiver there will be a command implementation. The application represents the Client. You can use it to retry, if a command cannot execute properly. Invoker object looks for the appropriate object which can handle this command and passes the command to the corresponding object which executes the command. 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