{"id":1654,"date":"2023-04-22T19:05:30","date_gmt":"2023-04-22T12:05:30","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=1654"},"modified":"2023-04-22T19:05:31","modified_gmt":"2023-04-22T12:05:31","slug":"csharp-facade-pattern","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-design-patterns\/csharp-facade-pattern\/","title":{"rendered":"C# Facade Pattern"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the C# Facade pattern to make a simple and clean interface to a larger and more complex subsystem.<\/p>\n\n\n\n

Introduction to the C# Facade pattern<\/h2>\n\n\n\n

The Facade pattern is a structural design pattern that allows you to create a simplified interface<\/a> to a complex subsystem.<\/p>\n\n\n\n

The Facade pattern exposes only the necessary functionality of the underlying subsystem while hiding the implementation details and complexities of the subsystem.<\/p>\n\n\n\n

The following diagram illustrates the Facade pattern:<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

In this diagram, the client classes interact with a simple interface (Facade) instead of working directly with subsystem classes. This makes the system more flexible so that when the subsystem classes change, you don’t need to modify the client classes.<\/p>\n\n\n\n

To use the Facade pattern in practice, you create a new class or set of classes that serve as an interface to the existing subsystem. <\/p>\n\n\n\n

This new interface provides a simplified set of methods that the client classes use to access the functionality of the subsystem. The client classes don’t need to know the implementation details or interact directly with the subsystem’s classes.<\/p>\n\n\n\n

C# Facade pattern example<\/h2>\n\n\n\n

The following program returns the current temperature in Celsius based on a city. It uses three classes GeoLookupService<\/code>, WeatherService<\/code>, and ConverterService<\/code> that provide geolocation lookup, weather, and converter services:<\/p>\n\n\n

namespace<\/span> FacacdePattern<\/span>;\n\npublic<\/span> class<\/span> Location<\/span>\n{\n    public<\/span> double<\/span> Latitude\n    {\n        get<\/span>; set<\/span>;\n    }\n    public<\/span> double<\/span> Longitude\n    {\n        get<\/span>; set<\/span>;\n    }\n    public<\/span> Location<\/span>(double<\/span> latitude, double<\/span> longitude<\/span>)<\/span>\n    {\n\n        Latitude = latitude;\n        Longitude = longitude;\n    }\n}\n\npublic<\/span> class<\/span> GeoLookupService<\/span>\n{\n    public<\/span> Location GetLocationByCity<\/span>(string<\/span> city<\/span>)<\/span>\n    {\n        return<\/span> new<\/span> Location(15<\/span>, 20<\/span>);\n    }\n}\npublic<\/span> class<\/span> WeatherService<\/span>\n{\n    public<\/span> double<\/span> GetCurrentTemperature<\/span>(Location location<\/span>)<\/span> => new<\/span> Random().Next(32<\/span>, 115<\/span>);\n}\n\npublic<\/span> class<\/span> ConverterService<\/span>\n{\n    public<\/span> double<\/span> ConvertFToC<\/span>(double<\/span> f<\/span>)<\/span> => (f - 32<\/span>) * 5<\/span> \/ 9<\/span>;\n}\n\n\npublic<\/span> class<\/span> Program<\/span>\n{\n    public<\/span> static<\/span> void<\/span> Main<\/span>(string<\/span>[] args<\/span>)<\/span>\n    {\n\n        var<\/span> geoLookupService = new<\/span> GeoLookupService();\n        var<\/span> location = geoLookupService.GetLocationByCity(\"San Jose\"<\/span>);\n\n        var<\/span> weatherService = new<\/span> WeatherService();\n        var<\/span> temperature = weatherService.GetCurrentTemperature(location); \n\n        var<\/span> converterService = new<\/span> ConverterService();\n        var<\/span> temperatureInC = converterService.ConvertFToC(temperature);\n\n        Console.WriteLine($\"The current temperature is {temperatureInC:F1}<\/span>\u00b0C\"<\/span>);\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
The current temperature is<\/span> 30.0<\/span>\u00b0C<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
How it works.<\/p>\n\n\n\n
First, define the Location<\/code> class that represents a geographical location with a latitude and longitude:<\/p>\n\n\n
public<\/span> class<\/span> Location<\/span>\n{\n    public<\/span> double<\/span> Latitude\n    {\n        get<\/span>; set<\/span>;\n    }\n    public<\/span> double<\/span> Longitude\n    {\n        get<\/span>; set<\/span>;\n    }\n    public<\/span> Location<\/span>(double<\/span> latitude, double<\/span> longitude<\/span>)<\/span>\n    {\n\n        Latitude = latitude;\n        Longitude = longitude;\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, define the GeoLookupService<\/code> class with a method GetLocationByCity()<\/code> that returns a Location object for a given city:<\/p>\n\n\n
public<\/span> class<\/span> GeoLookupService<\/span>\n{\n    public<\/span> Location GetLocationByCity<\/span>(string<\/span> city<\/span>)<\/span>\n    {\n        return<\/span> new<\/span> Location(15<\/span>, 20<\/span>);\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, define the WeatherService<\/code> class that returns the current temperature in Fahrenheit of a location:<\/p>\n\n\n
public<\/span> class<\/span> WeatherService<\/span>\n{\n    public<\/span> double<\/span> GetCurrentTemperature<\/span>(Location location<\/span>)<\/span> => new<\/span> Random().Next(32<\/span>, 115<\/span>);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The GetCurrentTemperature()<\/code> method returns a random temperature in Fahrenheit between 32 and 115. In practice, you may call an API to get the current temperature based on the current location of the user.<\/p>\n\n\n\n
Fourth, define the ConverterService<\/code> class that converts Fahrenheit to Celsius:<\/p>\n\n\n
public<\/span> class<\/span> ConverterService<\/span>\n{\n    public<\/span> double<\/span> ConvertFToC<\/span>(double<\/span> f<\/span>)<\/span> => (f - 32<\/span>) * 5<\/span> \/ 9<\/span>;\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Finally, use the above classes in the Client class to display the current temperature in Celsius to the console by using the above service classes:<\/p>\n\n\n
public<\/span> class<\/span> Client<\/span>\n{\n    public<\/span> static<\/span> void<\/span> Main<\/span>(string<\/span>[] args<\/span>)<\/span>\n    {\n        var<\/span> geoLookupService = new<\/span> GeoLookupService();\n        var<\/span> location = geoLookupService.GetLocationByCity(\"San Jose\"<\/span>);\n\n        var<\/span> weatherService = new<\/span> WeatherService();\n        var<\/span> temperature = weatherService.GetCurrentTemperature(location); \n\n        var<\/span> converterService = new<\/span> ConverterService();\n        var<\/span> temperatureInC = converterService.ConvertFToC(temperature);\n\n        Console.WriteLine($\"The current temperature is {temperatureInC:F1}<\/span>\u00b0C\"<\/span>);\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The program works fine except that it depends on many services of the subsystem. If one of the services changes, you need to modify the Client class accordingly. To make the Client class more flexible, you can apply the Facade pattern.<\/p>\n\n\n\n
Using the Facade pattern<\/h3>\n\n\n\n
First, define an interface IWeatherServiceFacade<\/code>:<\/p>\n\n\n
public<\/span> interface<\/span> IWeatherServiceFacade<\/span>\n{\n    double<\/span> GetCurrentTemperatureByCity<\/span>(string<\/span> city<\/span>)<\/span>;\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The IWeatherServiceFacade<\/code> interface has one method GetCurrentTemperatureByCity()<\/code> that returns the current temperature in Celsius of a city.<\/p>\n\n\n\n
Second, define the WeatherServiceFacade<\/code> class that implements the IWeatherServiceFacade<\/code> interface:<\/p>\n\n\n
public<\/span> class<\/span> WeatherServiceFacade<\/span> : IWeatherServiceFacade<\/span>\n{\n    private<\/span> readonly<\/span> GeoLookupService _geoLookupService;\n    private<\/span> readonly<\/span> WeatherService _weatherService;\n    private<\/span> readonly<\/span> ConverterService _converterService;\n    public<\/span> WeatherServiceFacade<\/span>(<\/span>)<\/span>\n    {\n        _geoLookupService = new<\/span> GeoLookupService();\n        _weatherService = new<\/span> WeatherService();\n        _converterService = new<\/span> ConverterService();\n    }\n    public<\/span> double<\/span> GetCurrentTemperatureByCity<\/span>(string<\/span> city<\/span>)<\/span>\n    {\n\n        var<\/span> location = _geoLookupService.GetLocationByCity(city);\n        var<\/span> temperature = _weatherService.GetCurrentTemperature(location);\n        return<\/span> _converterService.ConvertFToC(temperature);\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The GetCurrentTemperatureByCity()<\/code> method of the WeatherService<\/code>Facade<\/code> first uses the GeoLookupService<\/code> object to get the location of a city. Then, it uses the WeatherService<\/code> object to get the current temperature in Fahrenheit by location. And finally, it uses the UnitConvertService<\/code> to convert the temperature from Fahrenheit to Celsius.<\/p>\n\n\n\n
Now, the Client<\/code> class needs to use the IWeatherServiceFacade<\/code> object to get the current temperature of a city by calling the GetCurrentTemperatureByCity()<\/code> method. It doesn’t need to know the underlying services:<\/p>\n\n\n
public<\/span> class<\/span> Client<\/span>\n{\n    public<\/span> static<\/span> void<\/span> Main<\/span>(string<\/span>[] args<\/span>)<\/span>\n    {\n\n        var<\/span> weatherServiceFacade = new<\/span> WeatherServiceFacade();\n        var<\/span> temperatureInC = weatherServiceFacade.GetCurrentTemperatureByCity(\"San Jose\"<\/span>);\n\n        Console.WriteLine($\"The current temperature is {temperatureInC:F1}<\/span>\u00b0C\"<\/span>);\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Putting it all together.<\/p>\n\n\n
namespace<\/span> FacacdePattern<\/span>;\n\npublic<\/span> class<\/span> Location<\/span>\n{\n    public<\/span> double<\/span> Latitude\n    {\n        get<\/span>; set<\/span>;\n    }\n    public<\/span> double<\/span> Longitude\n    {\n        get<\/span>; set<\/span>;\n    }\n    public<\/span> Location<\/span>(double<\/span> latitude, double<\/span> longitude<\/span>)<\/span>\n    {\n\n        Latitude = latitude;\n        Longitude = longitude;\n    }\n}\n\npublic<\/span> class<\/span> GeoLookupService<\/span>\n{\n    public<\/span> Location GetLocationByCity<\/span>(string<\/span> city<\/span>)<\/span>\n    {\n        return<\/span> new<\/span> Location(15<\/span>, 20<\/span>);\n    }\n}\npublic<\/span> class<\/span> WeatherService<\/span>\n{\n    public<\/span> double<\/span> GetCurrentTemperature<\/span>(Location location<\/span>)<\/span> => new<\/span> Random().Next(32<\/span>, 115<\/span>);\n}\n\npublic<\/span> class<\/span> ConverterService<\/span>\n{\n    public<\/span> double<\/span> ConvertFToC<\/span>(double<\/span> f<\/span>)<\/span> => (f - 32<\/span>) * 5<\/span> \/ 9<\/span>;\n}\n\n\npublic<\/span> interface<\/span> IWeatherServiceFacade<\/span>\n{\n    double<\/span> GetCurrentTemperatureByCity<\/span>(string<\/span> city<\/span>)<\/span>;\n}\n\npublic<\/span> class<\/span> WeatherServiceFacade<\/span> : IWeatherServiceFacade<\/span>\n{\n    private<\/span> readonly<\/span> GeoLookupService _geoLookupService;\n    private<\/span> readonly<\/span> WeatherService _weatherService;\n    private<\/span> readonly<\/span> ConverterService _converterService;\n\n    public<\/span> WeatherServiceFacade<\/span>(<\/span>)<\/span>\n    {\n        _geoLookupService = new<\/span> GeoLookupService();\n        _weatherService = new<\/span> WeatherService();\n        _converterService = new<\/span> ConverterService();\n    }\n    public<\/span> double<\/span> GetCurrentTemperatureByCity<\/span>(string<\/span> city<\/span>)<\/span>\n    {\n\n        var<\/span> location = _geoLookupService.GetLocationByCity(city);\n        var<\/span> temperature = _weatherService.GetCurrentTemperature(location);\n        return<\/span> _converterService.ConvertFToC(temperature);\n    }\n}\n\npublic<\/span> class<\/span> Client<\/span>\n{\n    public<\/span> static<\/span> void<\/span> Main<\/span>(string<\/span>[] args<\/span>)<\/span>\n    {\n\n        var<\/span> weatherServiceFacade = new<\/span> WeatherServiceFacade();\n        var<\/span> temperatureInC = weatherServiceFacade.GetCurrentTemperatureByCity(\"San Jose\"<\/span>);\n\n        Console.WriteLine($\"The current temperature is {temperatureInC:F1}<\/span>\u00b0C\"<\/span>);\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary<\/h2>\n\n\n\n
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  • Use the Facade pattern to create a simple and clean interface to complex subsystems to make your applications more maintainable and flexible.<\/li>\n<\/ul>\n
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