DESIGN PATTERN FRAMEWORK 4.0 C# EBOOK
Data & Object Factory, LLC. All rights reserved Page 1 of 16 Design Pattern Framework™ 1. 4 Versions of Visual Studio myavr.info 4 1: Gang of Four (GoF). . C# Edition: C:\Users\%username%\Documents\DoFactory\DPF\\CS \*. C#, myavr.info, WPF, WCF, LINQ, PATTERNS home products and pricing In fact, our latest Design Pattern Framework is 9 packages in. NET features, such as, generics, attributes, delegates, reflection, and more. These and much more are available in myavr.info Design Pattern Framework
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and Events come in handy when the Observer pattern is to be used. However in C#, in chapter 4 we describe six of the design patterns presented by Gamma et . NET platform is a new development framework providing a new Application. Chapter 4. Other Consequences of the Singleton Pattern . Design Patterns: A Tutorial is a practical guide to writing C# programs using the most common . patterns incorporated in the GUI application framework, ET++. O'Reilly Media, Inc. C# Design Patterns, the image of a greylag goose, and Pattern Comparison. 4. Structural Patterns: Adapter and Façade. .. construction, or that adapters are prevalent in well-known graphical frameworks.
The example below will need adjustment. Page 15 of 86 Design Pattern Framework 4. In your own programs you most likely have created methods that return new objects.
However, not all methods that return a new object are Factory methods. So, when do you know the Factory Method is at work? The rules are: the method creates a new object the method returns an abstract class or interface the abstract class or interface is implemented by several classes Factory Method in. An example is the System.
Convert class which exposes many static methods that, given an instance of a type, returns another new type. For example, Convert. ToBoolean accepts a string and returns a boolean with value true or false depending on the string value true or false. Likewise the Parse method on many built-in value types Int32, Double, etc are examples of the same pattern.
Page 16 of 86 Design Pattern Framework 4. ToBoolean myString In. NET the Factory Method is typically implemented as a static method which creates an instance of a particular type determined at compile time.
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In other words, these methods dont return base classes or interface types of which the true type is only known at runtime. This is exactly where Abstract Factory and Factory Method differ: Abstract Factory methods are virtual or abstract and return abstract classes or interfaces.
Factory Methods are abstract and return class types. Two static factory method examples are File. Open and Activator. Page 17 of 86 7. Prototype Definition Specify the kind of objects to create using a prototypical instance, and create new objects by copying this prototype.
Page 18 of 86 Design Pattern Framework 4.
Structural Real-world sample code The real-world code demonstrates the Prototype pattern in which new Color objects are created by copying pre-existing, user-defined Colors of the same type. The abstract classes have been replaced by interfaces because the abstract classes contain no implementation code. RGB values range between , therefore the int has been replaced with a smaller byte data type.
The colors collection in the ColorManager class is implemented with a type-safe generic Dictionary class. In this implementation the key is of type string i. ICloneable is a built-in.
NET prototype interface. ICloneable requires that the class hierarchy be serializable. Here the Serializable attribute is used to do just that as an aside: if a class has 'event' members then these must be decorated with the NonSerialized attribute. Alternatively, reflection could have been used to query each member in the ICloneable class.
Tip: always be concerned about poor performance when implementing cloning many objects through serialization or reflection. Page 19 of 86 Code in project: DoFactory. NetOptimized Prototype: when and where use it Like other creational patterns Builder, Abstract Factory, and Factory Method , the Prototype design pattern hides object creation from the client.
However, instead of creating a non-initialized object, it returns a new object that is initialized with values it copied from a prototype - or sample - object. The Prototype design pattern is not commonly used in the construction of business applications. The Prototype design pattern creates clones of pre-existing sample objects. The best way to implement this in.
NET is to use the built-in ICloneable interface on the objects that are used as prototypes. The ICloneable interface has a method called Clone that returns an object that is a copy, or clone, of the original object. When implementing the Clone functionality you need to be aware of the two different types of cloning: deep copy versus shallow copy. Shallow copy is easier but only copies data fields in the object itself -- not the objects the prototype refers to. Deep copy copies the prototype object and all the objects it refers to.
Shallow copy is easy to implement because the Object base class has a MemberwiseClone method that returns a shallow copy of the object.
The copy strategy for deep copy may be more complicated -- some objects are not readily copied such as Threads, Database connections, etc.
You also need to watch out for circular references. Prototype in the. For instance, the selection is based on multiple parameters. For this, we can utilize a Func delegate.
You can specify multiple parameters to the selector and return the result you desire.
.NET Design Patterns
For more information on how to use Func delegate please refer to Func. This pattern allows us to execute a block of code using lambda expression.
However this pattern is about using lambda expressions and implements a coding style, which will enhance one of the existing popular Design Patterns. We would write code similar to the following:. In a real world example, there can be so many objects having a large object graph, trying to create database connections and timing out. The obvious solution is to clean-up the resources explicitly and as quickly as possible. Note that we have not removed the Finalizer yet.
For each database creation Cleanup will perform explicitly. As we saw in the first for loop example, at the end of the loop, the resources will be garbage collected.
One of the problems with this approach is that if there is an exception in one of the Query operations, the clean-up operation would never get called. Technically this solves the problem. As the clean-up operation always gets invoked regardless of whether there is an exception or not. However this approach still has some other issues.
To make things worse, in more complex situations, we can even introduce bugs without knowing which operation to call etc. This is where most of us would use the well-known Dispose Pattern. The IDisposable. Dispose method cleans-up the resources at the end of the operations.
This includes any exception scenarios during query operations. This is definitely a much better way to write the code. The using block abstracts away the dispose of the object. It guarantees that the clean-up will occur using Dispose routine. Most of us would settle with this approach. You will see this pattern used in many applications.
NET Design Pattern Framework 4.5
But if we really look closely there is still a problem with the using pattern itself. Technically it will do right thing by explicitly cleaning-up resources. But there is no guarantee that the client of the API would use the using block to clean-up-up the resources.
For example, anyone can still write the following code:. For resource intensive applications, if this code has been committed without being noticed, this can have an adverse effect on the application. So we are back to square one.
As we have noticed, there is no immediate dispose or clean-up operation that takes place. A chance of missing the Dispose method is a serious problem.
This is all unnecessary trouble to go through. So in order to address these issues, it would be ideal if we can change the API in such a way that developers cannot make mistakes.
This is where we can use Lambda Expressions to resolve these issues. In order to implement the Execute Around Pattern with Lambda Expressions we will modify the code with the following:. There are few interesting things happening here. IDisposable implementation has been removed. The constructor of this class becomes private.
So the design has been enforced in such a way that the user cannot directly instantiate the Database instance. Similarly the Cleanup method is also private.
There is a new Create method, which takes an Action delegate which accepts an instance of the database as a parameter. The implementation of this method would execute the action specified by the Action parameter.
This approach becomes very natural as all boilerplate code has been abstracted away from the client. This way it is hard to imagine that the developer would make a mistake.
Obviously this pattern is not limited to managing resources of a database. It has so many other potentials. Here are some of its applications. NET Garbage collection. This is quite interesting. Please see below. There is a limitation on the usage of this attribute where we cannot specify the exact call that throws an exception during the test execution. This code demoes a typical implementation of an ExpectedException attribute. Note that we expect sut. SomeMethod would throw an exception.
Note that I have removed the detailed implementation for code brevity. During test execution, if there is an exception being thrown, it will be caught and the test would succeed. However the test would not know exactly where the exception has been thrown. For example, it could be during the creation of the SytemUnderTest.
This is by creating a helper method, which accepts an Action parameter as delegate. The above ExceptionAssert. Throws can be used to explicitly invoke the method that throws the exception. These frameworks already have built-in helper methods implemented using this pattern to target the exact operation that cause exception.
In this article we looked at various. Design Patterns are good but they only become effective if we can use them correctly.
We would like to think Design Patterns as a set of tools which allow us to make better decisions on the code base. We would also like to treat them as communication tools so we can improve the communication around the code base.
We have also looked at applying a slightly different approach to the existing Design Patterns using lambda expressions. Throughout this article we saw that Lambda Expressions are a great way to enhance the power of some of the well-known Software Patterns. This article has been editorially reviewed by Suprotim Agarwal. C and. Organized around concepts, this eBook aims to provide a concise, yet solid foundation in C and.
NET, covering C 6. NET Core, with chapters on. NET Standard and the upcoming C 8. Use these concepts to deepen your existing knowledge of C and. NET, to have a solid grasp of the latest in C and. NET OR to crack your next.
NET Interview. This article focuses on.
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NET Design Patterns using C and takes a fresh view of some of the existing ones and see how we can go about using them in real world dilemmas and concerns. Abstract Factory Pattern Wikipedia definition: Please refer to the following example: Book", new Dictionary As per the above example, creation of instances are delegated to a routine called CreateInstances.
This routine takes a class name and the property values as arguments.
NET 4. What others are saying Below is an unsolicited letter from Miguel A. NET, a well-known. NET author,. NET trainer, and a member of the International. Quite a package you guys put together there - code and docs. You've managed to compile for me what I've been grabbing from various sources over a long time. I'm very impressed.This may not be obvious at this stage. But the approach becomes very powerful when we want to dynamically create instances based on parameters.
A Singleton removes the need to constantly create and destroy objects.
ToBoolean accepts a string and returns a boolean with value true or false depending on the string value true or false. We would write code similar to the following: This is where we can take the advantage of lambda expressions and make the intention explicit to the consumer of this API.