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It allows the chef to start cooking right away instead of running around clarifying the order details from you directly. Let’s have a look on the Abstract Command class which will be inherited by all Concrete Command which are applicable on our final receiver class Radio. If you already use the Command Pattern in your application, adding Undo/Redo logic is relatively straightforward. Which of the two strategies you choose will also affect the "weight" of your commands.
Software Design Pattern in Development
Use the Command pattern when you want to queue operations, schedule their execution, or execute them remotely. Your current task is to create a toolbar with a bunch of buttons for various operations of the editor. You created a very neat Button class that can be used for buttons on the toolbar, as well as for generic buttons in various dialogs. Generic model class diagram of Command design pattern is as shown in image. All clients of Command objects treat each object as a "black box" bysimply invoking the object's virtual execute() method whenever theclient requires the object's "service".
Some other Popular Design Patterns
Here, the Execute method will call the Save Method of the Document Object. In the same order, the Close Command has the request to close the document. The Execute Method will call the Close Method of the document object. As per the Command Design Pattern, the Command Object will be passed to the Invoker Object. The Invoker Object does not know how to handle the request.
Command Design Pattern in C#
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You might have noticed one missing piece of the puzzle, which is the request parameters. A GUI object might have supplied the business-layer object with some parameters. Since the command execution method doesn’t have any parameters, how would we pass the request details to the receiver? It turns out the command should be either pre-configured with this data, or capable of getting it on its own. Command objects serve as links between various GUI and business logic objects. From now on, the GUI object doesn’t need to know what business logic object will receive the request and how it’ll be processed.
When to Use Command Pattern
We will implement command design pattern for the remote application discussed in the above section. You will also have to consider how you want to undo delete operations. A common approach here is to use a soft delete strategy, meaning you mark deleted entities with a flag and filter them out during requests.
Usually it has just a single execution method that takes no parameters. This interface lets you use various commands with the same request sender, without coupling it to concrete classes of commands. As a bonus, now you can switch command objects linked to the sender, effectively changing the sender’s behavior at runtime. Command is a behavioral design pattern that turns a request into a stand-alone object that contains all information about the request. This transformation lets you pass requests as a method arguments, delay or queue a request’s execution, and support undoable operations.
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Now we need to create implementations for all the different types of action performed by the receiver. Since we have three actions we will create three Command implementations. Each Command implementation will forward the request to the appropriate method of receiver. You’ll implement a bunch of command classes for every possible operation and link them with particular buttons, depending on the buttons’ intended behavior.
Behvioural Design Patterns
Now that our receiver classes are ready, we can move to implement our Command classes. FileSystemReceiver interface defines the contract for the implementation classes. For simplicity, I am creating two flavors of receiver classes to work with Unix and Windows systems.
To be able to revert operations, you need to implement the history of performed operations. The command history is a stack that contains all executed command objects along with related backups of the application’s state. Consequently, this can lead to code that’s harder to read and maintain.
If you don’t need to perform actions later, you may be better off simply calling the receiver’s methods directly. The Command design pattern allows to encapsulate an action or trigger inside an object which will be used later to trigger an event. Since in this design pattern, commands are encapsulated inside objects, hence we can use additional actions on this commands for example- Queuing of various commands, undo/redo actions etc. This design pattern is very useful in case of GUI actions (button, menu actions etc), transactional behaviour, progress bars etc. For Design patterns basic explanation see (Design Patterns Simplified Version).
We create the Command interface which will be implemented by the concrete command classes. The text editor in this example creates new command objects each time a user interacts with it. After executing its actions, a command is pushed to the history stack. So, modify the Main method of the Program class as shown below. First, we create an instance of the Receiver Object, i.e., Document. Then, we create three command objects by passing the Receiver Object as a parameter, i.e., the Document object.
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