Welcome!

.NET Authors: Sandi Mappic, Yeshim Deniz, Carmen Gonzalez, Greg O'Connor, Pat Romanski

Related Topics: .NET

.NET: Article

Implementing Patterns with Generics

It's more than just collections

It's been a few months since Visual Studio 2005 was released. In that time you've probably seen and read quite a bit about generics. Unfortunately all those articles and presentations can leave you with the impression that generics are useful only in the context of collections (List<T>, Dictionary<K,V>, Queue<T>, and so on).

It's true that many of the most common uses of generics involve collections. But limiting your use to collections will cause you to miss many of the opportunities for creating components that you can reuse in even more ways. In fact, many idioms where developers commonly copy, paste, and modify source code can be solved with generics. You should look for these opportunities, because you'll have more functionality in a smaller code base.

Enhance a generic class, and all users of it are one recompile away from the new features. That's much better than using code snippets. It's a manual task to track down and edit all the copies of a code snippet inserted into your project.

In this article, I'll show you how to find algorithms that can be replaced with generics and how to migrate specific code to its generic counterpart. As examples, I'll show you a quick example by serializing types as XML data, and I'll build a more complicated version, implementing the Proxy class from Design Patterns (Addison-Wesley, 1995).

The Sample Application
To illustrate these topics, I built a simple application that enables you build a collage from a list of images. (See Figure 1.) This is a small sample to illustrate the concepts, so keep your copy of Photoshop for now. The sample application lets you choose a source directory for your images, copy the images onto a background, and move and scale the images. Once you have something you like, you can save the composite image.

We'll examine this application and extract two generic algorithms that you can reuse in your own applications.

Making Generics
Generics are the .NET way of creating algorithms that are loosely coupled to the types on which they operate. That's a large part of the reason why so many of the examples use collections. Collection algorithms don't normally have any dependencies on the types contained in the collections. List<int>, List<string>, List<Employee>, or anything else would work just fine.

The implementation of the collection classes isn't dependent on any properties, or behavior, defined in the type contained. In fact, different generic collections only differ in the capabilities of the collection itself; rarely do they differ in the constraints mandated on the contained type.

In my example, I've used a List<Image> for the list of images in the current collage. The list of files is a BindingList<string> because the BindingList<T> class contains extra functionality that facilitates data binding in Windows forms applications. You've probably already used both of these classes.

Another area where you can see generics used in the .NET Framework is in interfaces that are often used in collections: IEquatable<T>, IEqualityComparer<T>, and ICompar-able<T>. Once again the key to using generics is that signature of the interface is very common: The implementation will depend on the specific type and the parameters depend on the specific type, but the semantic contract is independent of the type.

So the .NET Framework has a rich set of generic classes that are great for various common uses. These classes are designed for very horizontal applications. But they probably aren't all the reusable bits of functionality you'll use in your applications or across multiple applications in your organization. As you develop more code, you'll discover that you've written bits of functionality that you want to reuse in many different ways. With a little work, you can modify these bits of code so that you can reuse them, unmodified, in many different ways.

The first example will provide a mechanism to store and retrieve the current application state. Most desktop applications will store some form of user preferences, or last actions, or similar data. I find that persisting that information using the .NET XML serialization framework is an easy way to implement that. You write a simple class that contains public properties for all the user-controlled options. Then you write two methods to load and save the options. My sample application used the specific UserPreferences class shown in Listing 1.

You'll notice that the LoadFromFile and SaveToFile methods are almost completely independent of the type used (UserSettings). You should be able to reuse these methods anywhere, right? You can. Simply factor out those two methods and put them in a generic class. The wrapper class contains a single member of the target type and provides the load and save code. It also provides a read-only property to access the embedded target object. Limiting the target object to a class type enables you to add a read-only property to modify the embedded storage and still provide appropriate access to the embedded object for the rest of the program. The generic wrapper is shown in Listing 2.

Reusing this is a simple matter of creating a new instantiation with different type information. As an example, let's add the ability of saving your current work to the sample application. Doing so will leverage the AutoSave generic class. Inside the Main form, you've got a list of images:

private List<CollageImage> listOf-Images = new List<CollageImage>();

Essentially, that's the entire storage for the current collage. So let's make a couple of modifications to the CollageImage class that will make it easier to save that via XML serialization. The images need the XMLIgnore attribute:

[XmlIgnore()]
public Image Thumbnail
{
      get
      {
         generateThumbnail();
         return thumbNail;
      }
}

      And the image path must be a read/write property:

public string ImagePath
{
      get { return path; }
      set { path = value; }
}

Next, let's build a simple class that contains the list of images. (See Listing 3.) There is one interesting problem in the generic collections with respect to XML Serialization. For some reason, the XML Serializer can't save or restore a generic IList<T>, but it can serialize and IList interface, provided the appropriate attributes are added to the property. Therefore, I've added two different IList properties to this class, one IList<CollageImage>, one IList. The second is correctly serialized.

Finally, you can use the AutoSave template to create a version of this class that can be serialized. That's it. The point is that you can reuse the AutoSave generic class with only minimal extra work.

Pondering Patterns
Load and save was fairly simple, so let's move on to the more complicated Proxy pattern. Stripped of all the glamour normally associated with a new buzzword, a design pattern is simply a standard proven solution to a common programming problem. Nothing more; nothing less. As such it's a way to reuse common solutions to common problems. Design Patterns by Gamma, Helm, Johnson, and Vlissides (Addison-Wesley, 1995) is still the definitive catalog of patterns.


More Stories By Bill Wagner

A frequent writer and speaker, Bill's work is published in ASP.NET Pro and Visual Studio Magazine. He is the author of C# Core Language Little Black Book and Effective C#. You can reach Bill at [email protected]

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
Samsung VP Jacopo Lenzi, who headed the company's recent SmartThings acquisition under the auspices of Samsung's Open Innovaction Center (OIC), answered a few questions we had about the deal. This interview was in conjunction with our interview with SmartThings CEO Alex Hawkinson. IoT Journal: SmartThings was developed in an open, standards-agnostic platform, and will now be part of Samsung's Open Innovation Center. Can you elaborate on your commitment to keep the platform open? Jacopo Lenzi: Samsung recognizes that true, accelerated innovation cannot be driven from one source, but requires a...
SYS-CON Events announced today that Red Hat, the world's leading provider of open source solutions, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Red Hat is the world's leading provider of open source software solutions, using a community-powered approach to reliable and high-performing cloud, Linux, middleware, storage and virtualization technologies. Red Hat also offers award-winning support, training, and consulting services. As the connective hub in a global network of enterprises, partners, a...
P2P RTC will impact the landscape of communications, shifting from traditional telephony style communications models to OTT (Over-The-Top) cloud assisted & PaaS (Platform as a Service) communication services. The P2P shift will impact many areas of our lives, from mobile communication, human interactive web services, RTC and telephony infrastructure, user federation, security and privacy implications, business costs, and scalability. In his session at Internet of @ThingsExpo, Robin Raymond, Chief Architect at Hookflash Inc., will walk through the shifting landscape of traditional telephone a...
BSQUARE is a global leader of embedded software solutions. We enable smart connected systems at the device level and beyond that millions use every day and provide actionable data solutions for the growing Internet of Things (IoT) market. We empower our world-class customers with our products, services and solutions to achieve innovation and success. For more information, visit www.bsquare.com.
SYS-CON Events announced today that Matrix.org has been named “Silver Sponsor” of Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Matrix is an ambitious new open standard for open, distributed, real-time communication over IP. It defines a new approach for interoperable Instant Messaging and VoIP based on pragmatic HTTP APIs and WebRTC, and provides open source reference implementations to showcase and bootstrap the new standard. Our focus is on simplicity, security, and supporting the fullest feature set.
How do APIs and IoT relate? The answer is not as simple as merely adding an API on top of a dumb device, but rather about understanding the architectural patterns for implementing an IoT fabric. There are typically two or three trends: Exposing the device to a management framework Exposing that management framework to a business centric logic • Exposing that business layer and data to end users. This last trend is the IoT stack, which involves a new shift in the separation of what stuff happens, where data lives and where the interface lies. For instance, it’s a mix of architectural style...
SYS-CON Events announced today that SOA Software, an API management leader, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. SOA Software is a leading provider of API Management and SOA Governance products that equip business to deliver APIs and SOA together to drive their company to meet its business strategy quickly and effectively. SOA Software’s technology helps businesses to accelerate their digital channels with APIs, drive partner adoption, monetize their assets, and achieve a...
From a software development perspective IoT is about programming "things," about connecting them with each other or integrating them with existing applications. In his session at @ThingsExpo, Yakov Fain, co-founder of Farata Systems and SuranceBay, will show you how small IoT-enabled devices from multiple manufacturers can be integrated into the workflow of an enterprise application. This is a practical demo of building a framework and components in HTML/Java/Mobile technologies to serve as a platform that can integrate new devices as they become available on the market.
SYS-CON Events announced today that Utimaco will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Utimaco is a leading manufacturer of hardware based security solutions that provide the root of trust to keep cryptographic keys safe, secure critical digital infrastructures and protect high value data assets. Only Utimaco delivers a general-purpose hardware security module (HSM) as a customizable platform to easily integrate into existing software solutions, embed business logic and build s...
Connected devices are changing the way we go about our everyday life, from wearables to driverless cars, to smart grids and entire industries revolutionizing business opportunities through smart objects, capable of two-way communication. But what happens when objects are given an IP-address, and we rely on that connection, sometimes with our lives? How do we secure those vast data infrastructures and safe-keep the privacy of sensitive information? This session will outline how each and every connected device can uphold a core root of trust via a unique cryptographic signature – a “bir...
Internet of @ThingsExpo Silicon Valley announced on Thursday its first 12 all-star speakers and sessions for its upcoming event, which will take place November 4-6, 2014, at the Santa Clara Convention Center in California. @ThingsExpo, the first and largest IoT event in the world, debuted at the Javits Center in New York City in June 10-12, 2014 with over 6,000 delegates attending the conference. Among the first 12 announced world class speakers, IBM will present two highly popular IoT sessions, which will take place November 4-6, 2014 at the Santa Clara Convention Center in Santa Clara, Calif...
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity.
WebRTC defines no default signaling protocol, causing fragmentation between WebRTC silos. SIP and XMPP provide possibilities, but come with considerable complexity and are not designed for use in a web environment. In his session at Internet of @ThingsExpo, Matthew Hodgson, technical co-founder of the Matrix.org, will discuss how Matrix is a new non-profit Open Source Project that defines both a new HTTP-based standard for VoIP & IM signaling and provides reference implementations.

SUNNYVALE, Calif., Oct. 20, 2014 /PRNewswire/ -- Spansion Inc. (NYSE: CODE), a global leader in embedded systems, today added 96 new products to the Spansion® FM4 Family of flexible microcontrollers (MCUs). Based on the ARM® Cortex®-M4F core, the new MCUs boast a 200 MHz operating frequency and support a diverse set of on-chip peripherals for enhanced human machine interfaces (HMIs) and machine-to-machine (M2M) communications. The rich set of periphera...

SYS-CON Events announced today that Aria Systems, the recurring revenue expert, has been named "Bronze Sponsor" of SYS-CON's 15th International Cloud Expo®, which will take place on November 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Aria Systems helps leading businesses connect their customers with the products and services they love. Industry leaders like Pitney Bowes, Experian, AAA NCNU, VMware, HootSuite and many others choose Aria to power their recurring revenue business and deliver exceptional experiences to their customers.
The Internet of Things (IoT) is going to require a new way of thinking and of developing software for speed, security and innovation. This requires IT leaders to balance business as usual while anticipating for the next market and technology trends. Cloud provides the right IT asset portfolio to help today’s IT leaders manage the old and prepare for the new. Today the cloud conversation is evolving from private and public to hybrid. This session will provide use cases and insights to reinforce the value of the network in helping organizations to maximize their company’s cloud experience.
The Internet of Things (IoT) is making everything it touches smarter – smart devices, smart cars and smart cities. And lucky us, we’re just beginning to reap the benefits as we work toward a networked society. However, this technology-driven innovation is impacting more than just individuals. The IoT has an environmental impact as well, which brings us to the theme of this month’s #IoTuesday Twitter chat. The ability to remove inefficiencies through connected objects is driving change throughout every sector, including waste management. BigBelly Solar, located just outside of Boston, is trans...
SYS-CON Events announced today that Matrix.org has been named “Silver Sponsor” of Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Matrix is an ambitious new open standard for open, distributed, real-time communication over IP. It defines a new approach for interoperable Instant Messaging and VoIP based on pragmatic HTTP APIs and WebRTC, and provides open source reference implementations to showcase and bootstrap the new standard. Our focus is on simplicity, security, and supporting the fullest feature set.
Predicted by Gartner to add $1.9 trillion to the global economy by 2020, the Internet of Everything (IoE) is based on the idea that devices, systems and services will connect in simple, transparent ways, enabling seamless interactions among devices across brands and sectors. As this vision unfolds, it is clear that no single company can accomplish the level of interoperability required to support the horizontal aspects of the IoE. The AllSeen Alliance, announced in December 2013, was formed with the goal to advance IoE adoption and innovation in the connected home, healthcare, education, aut...
SYS-CON Events announced today that Red Hat, the world's leading provider of open source solutions, will exhibit at Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Red Hat is the world's leading provider of open source software solutions, using a community-powered approach to reliable and high-performing cloud, Linux, middleware, storage and virtualization technologies. Red Hat also offers award-winning support, training, and consulting services. As the connective hub in a global network of enterprises, partners, a...