Click here to close now.


Microsoft Cloud Authors: Elizabeth White, Andreas Grabner, Jim Kaskade, Pat Romanski, David Bermingham

Related Topics: Microsoft Cloud

Microsoft Cloud: 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:

public Image Thumbnail
         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
“The Internet of Things transforms the way organizations leverage machine data and gain insights from it,” noted Splunk’s CTO Snehal Antani, as Splunk announced accelerated momentum in Industrial Data and the IoT. The trend is driven by Splunk’s continued investment in its products and partner ecosystem as well as the creativity of customers and the flexibility to deploy Splunk IoT solutions as software, cloud services or in a hybrid environment. Customers are using Splunk® solutions to collect and correlate data from control systems, sensors, mobile devices and IT systems for a variety of Ind...
Apps and devices shouldn't stop working when there's limited or no network connectivity. Learn how to bring data stored in a cloud database to the edge of the network (and back again) whenever an Internet connection is available. In his session at 17th Cloud Expo, Bradley Holt, Developer Advocate at IBM Cloud Data Services, will demonstrate techniques for replicating cloud databases with devices in order to build offline-first mobile or Internet of Things (IoT) apps that can provide a better, faster user experience, both offline and online. The focus of this talk will be on IBM Cloudant, Apa...
As enterprises capture more and more data of all types – structured, semi-structured, and unstructured – data discovery requirements for business intelligence (BI), Big Data, and predictive analytics initiatives grow more complex. A company’s ability to become data-driven and compete on analytics depends on the speed with which it can provision their analytics applications with all relevant information. The task of finding data has traditionally resided with IT, but now organizations increasingly turn towards data source discovery tools to find the right data, in context, for business users, d...
Clearly the way forward is to move to cloud be it bare metal, VMs or containers. One aspect of the current public clouds that is slowing this cloud migration is cloud lock-in. Every cloud vendor is trying to make it very difficult to move out once a customer has chosen their cloud. In his session at 17th Cloud Expo, Naveen Nimmu, CEO of Clouber, Inc., will advocate that making the inter-cloud migration as simple as changing airlines would help the entire industry to quickly adopt the cloud without worrying about any lock-in fears. In fact by having standard APIs for IaaS would help PaaS expl...
Organizations already struggle with the simple collection of data resulting from the proliferation of IoT, lacking the right infrastructure to manage it. They can't only rely on the cloud to collect and utilize this data because many applications still require dedicated infrastructure for security, redundancy, performance, etc. In his session at 17th Cloud Expo, Emil Sayegh, CEO of Codero Hosting, will discuss how in order to resolve the inherent issues, companies need to combine dedicated and cloud solutions through hybrid hosting – a sustainable solution for the data required to manage I...
SYS-CON Events announced today that IBM Cloud Data Services has been named “Bronze Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. IBM Cloud Data Services offers a portfolio of integrated, best-of-breed cloud data services for developers focused on mobile computing and analytics use cases.
SYS-CON Events announced today that ProfitBricks, the provider of painless cloud infrastructure, will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. ProfitBricks is the IaaS provider that offers a painless cloud experience for all IT users, with no learning curve. ProfitBricks boasts flexible cloud servers and networking, an integrated Data Center Designer tool for visual control over the cloud and the best price/performance value available. ProfitBricks was named one of the coolest Clo...
Learn how IoT, cloud, social networks and last but not least, humans, can be integrated into a seamless integration of cooperative organisms both cybernetic and biological. This has been enabled by recent advances in IoT device capabilities, messaging frameworks, presence and collaboration services, where devices can share information and make independent and human assisted decisions based upon social status from other entities. In his session at @ThingsExpo, Michael Heydt, founder of Seamless Thingies, will discuss and demonstrate how devices and humans can be integrated from a simple clust...
As more and more data is generated from a variety of connected devices, the need to get insights from this data and predict future behavior and trends is increasingly essential for businesses. Real-time stream processing is needed in a variety of different industries such as Manufacturing, Oil and Gas, Automobile, Finance, Online Retail, Smart Grids, and Healthcare. Azure Stream Analytics is a fully managed distributed stream computation service that provides low latency, scalable processing of streaming data in the cloud with an enterprise grade SLA. It features built-in integration with Azur...
You have your devices and your data, but what about the rest of your Internet of Things story? Two popular classes of technologies that nicely handle the Big Data analytics for Internet of Things are Apache Hadoop and NoSQL. Hadoop is designed for parallelizing analytical work across many servers and is ideal for the massive data volumes you create with IoT devices. NoSQL databases such as Apache HBase are ideal for storing and retrieving IoT data as “time series data.”
SYS-CON Events announced today that HPM Networks will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. For 20 years, HPM Networks has been integrating technology solutions that solve complex business challenges. HPM Networks has designed solutions for both SMB and enterprise customers throughout the San Francisco Bay Area.
Mobile messaging has been a popular communication channel for more than 20 years. Finnish engineer Matti Makkonen invented the idea for SMS (Short Message Service) in 1984, making his vision a reality on December 3, 1992 by sending the first message ("Happy Christmas") from a PC to a cell phone. Since then, the technology has evolved immensely, from both a technology standpoint, and in our everyday uses for it. Originally used for person-to-person (P2P) communication, i.e., Sally sends a text message to Betty – mobile messaging now offers tremendous value to businesses for customer and empl...
SYS-CON Events announced today that MobiDev, a software development company, will exhibit at the 17th International Cloud Expo®, which will take place November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. MobiDev is a software development company with representative offices in Atlanta (US), Sheffield (UK) and Würzburg (Germany); and development centers in Ukraine. Since 2009 it has grown from a small group of passionate engineers and business managers to a full-scale mobile software company with over 150 developers, designers, quality assurance engineers, project manage...
The broad selection of hardware, the rapid evolution of operating systems and the time-to-market for mobile apps has been so rapid that new challenges for developers and engineers arise every day. Security, testing, hosting, and other metrics have to be considered through the process. In his session at Big Data Expo, Walter Maguire, Chief Field Technologist, HP Big Data Group, at Hewlett-Packard, will discuss the challenges faced by developers and a composite Big Data applications builder, focusing on how to help solve the problems that developers are continuously battling.
SYS-CON Events announced today that Cloud Raxak has been named “Media & Session Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Raxak Protect automates security compliance across private and public clouds. Using the SaaS tool or managed service, developers can deploy cloud apps quickly, cost-effectively, and without error.
Who are you? How do you introduce yourself? Do you use a name, or do you greet a friend by the last four digits of his social security number? Assuming you don’t, why are we content to associate our identity with 10 random digits assigned by our phone company? Identity is an issue that affects everyone, but as individuals we don’t spend a lot of time thinking about it. In his session at @ThingsExpo, Ben Klang, Founder & President of Mojo Lingo, will discuss the impact of technology on identity. Should we federate, or not? How should identity be secured? Who owns the identity? How is identity ...
SYS-CON Events announced today that Solgeniakhela will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Solgeniakhela is the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions. Designed to “Bridge the Gap” between Personal and Professional Social, Mobile and Cloud user experiences, our solutions help large and medium-sized organizations dramatically improve productivity, reduce collaboration costs, and increase the overall enterprise value by bringing ...
Sensors and effectors of IoT are solving problems in new ways, but small businesses have been slow to join the quantified world. They’ll need information from IoT using applications as varied as the businesses themselves. In his session at @ThingsExpo, Roger Meike, Distinguished Engineer, Director of Technology Innovation at Intuit, will show how IoT manufacturers can use open standards, public APIs and custom apps to enable the Quantified Small Business. He will use a Raspberry Pi to connect sensors to web services, and cloud integration to connect accounting and data, providing a Bluetooth...
SYS-CON Events announced today that Micron Technology, Inc., a global leader in advanced semiconductor systems, will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Micron’s broad portfolio of high-performance memory technologies – including DRAM, NAND and NOR Flash – is the basis for solid state drives, modules, multichip packages and other system solutions. Backed by more than 35 years of technology leadership, Micron's memory solutions enable the world's most innovative computing, consumer,...
Nowadays, a large number of sensors and devices are connected to the network. Leading-edge IoT technologies integrate various types of sensor data to create a new value for several business decision scenarios. The transparent cloud is a model of a new IoT emergence service platform. Many service providers store and access various types of sensor data in order to create and find out new business values by integrating such data.