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The presentation layer contains the components that implement and display the user interface and manage user interaction.
The following steps describe the process you should adopt when designing the presentation layer for your application.
There are several key factors that you should consider when designing your presentation layer.
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Composition * Failing to consider use of patterns and libraries that support dynamic layout and injection of views and presentation at runtime.
Using presentation components that have dependencies on support classes and services instead of considering patterns that support run-time dependency injection.
Failing to design for different device and input types, such as mobile devices, touch-screen, and pen and ink–enabled devices. Caching is one of the best mechanisms you can use to improve application performance and UI responsiveness. If your application is deployed in Web farm, avoid using local caches that need to be synchronized; instead, consider using a transactional resource manager such as Microsoft SQL Server® or a product that supports distributed caching. Consider whether your application will be easier to develop and maintain if the presentation layer uses independent modules and views that are easily composed at run time. Design a centralized exception-management mechanism for your application that catches and throws exceptions consistently.
Design a global exception handler that displays a global error page or an error message for all unhandled exceptions. Use a document-based input mechanism for collecting input in Microsoft Office–style documents. Implement a wizard-based approach for more complex data collection tasks, or for input that requires a workflow. Design to support localization by avoiding hard-coded strings and using external resources for text and layout. Design your UI layout so that the layout mechanism itself is separate from the individual UI components and UI process components.
Use a common look and feel for all elements of your UI to maximize accessibility and ease of use. Use design patterns, such as Model-View-Presenter (MVP), to separate the layout design from interface processing. Design your navigation strategy so that users can navigate easily through your screens or pages, and so that you can separate navigation from presentation and UI processing. Use well-known design patterns to decouple the UI from the navigation logic where this logic is complex. Determine how you will preserve navigation state if the application must preserve this state between sessions.
Use presentation entities to store the data you will use in your presentation layer to manage your views.
If you are working with data-bound controls, consider using custom objects, collections, or datasets as your presentation entity format. If you want to map data directly to business entities, use a custom class for your presentation entities. If you need to perform data type validation, consider adding it in your presentation entities.
Design your request processing with user responsiveness in mind, as well as code maintainability and testability.
Use asynchronous operations or worker threads to avoid blocking the UI for long-running actions.
Consider using the Passive View pattern (a variant of MVP) for interfaces that do not manage a lot of data. Consider using the Supervising Controller pattern (a variant of MVP) for interfaces that manage large amounts of data.
When developing a rich Internet application (RIA), avoid synchronous processing where possible. When developing a Web application, consider using Asynchronous JavaScript and XML (AJAX) to improve responsiveness and to reduce post backs and page reloads. UI components are the controls and components used to display information to the user and accept user input. Create custom controls or use third-party controls only for specialized display and data-collection tasks. When creating custom controls, extend existing controls if possible instead of creating a new control. Consider implementing designer support for custom controls to make it easier to develop with them. Consider maintaining the state of controls as the user interacts with the application instead of reloading controls with each action.
If your UI requires complex processing or needs to talk to other layers, use UI process components to decouple this processing from the UI.
Avoid business rules, with the exception of input and data validation, in UI processing components. Consider using abstraction patterns, such as dependency inversion, when UI processing behavior needs to change based on the run-time environment. Where the UI requires complex workflow support, create separate workflow components that use a workflow system such as Windows Workflow or a custom mechanism. Designing an effective input and data-validation strategy is critical to the security of your application. Validate all input data on the client side where possible to improve interactivity and reduce errors caused by invalid data. Key patterns are organized by key categories, as detailed in the Presentation Layer Frame in the following table.
If you want to build full-featured connected, occasionally connected, and disconnected executable applications that run on a wide range of Microsoft Windows®–based devices, consider using the Microsoft Windows Compact Framework. If you want to build applications that support rich media and interactivity, consider using Microsoft Silverlight® for Mobile.
If you want to build applications with good performance and interactivity, and have design support in Microsoft Visual Studio®, consider using Windows Forms. If you want to build applications that fully support rich media and graphics, consider using Windows Presentation Foundation (WPF).
If you want to build applications that are downloaded from a Web server and then execute on the client, consider using XAML Browser Applications (XBAP). If you want to build applications that are predominantly document-based, or are used for reporting, consider designing a Microsoft Office Business Application. If you decide to use Windows Forms and you are designing composite interfaces, consider using the Smart Client Software Factory.
If you decide to use WPF and you are designing composite interfaces, consider using the Composite Application Guidance for WPF. If you decide to use WPF, consider using the Presentation Model (Model-View-ViewModel) pattern. If you decide to use WPF, consider using WPF Commands to communicate between your View and your Presenter or ViewModel. If you decide to use WPF, consider implementing the Presentation Model pattern by using DataTemplates over User Controls to give designers more control.
If you want to build browser-based, connected applications that have broad cross-platform reach, are highly graphical, and support rich media and presentation features, consider using Silverlight. If you decide to use Silverlight, consider using the Presentation Model (Model-View-ViewModel) pattern.
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Before launching into the design patterns, let’s go over some basics of network programming with BSD Sockets. The Internet model is a subset of the Open Systems Interconect (OSI) model that describes how network protocols and equipment should interoperate.
The Internet application layer combines the application, presentation and session layers of the OSI model.
At the bottom of the OSI stack is the datalink and physical layers which map to a single Network Link layer in the Internet model. Both TCP and UDP protocols live in the transport layer and add the concept of ports to differentiate applications running on a given host.
To establish TCP connections the server host calls socket() to create a listening socket then specifies the IP address and TCP port on which the server will receive connection requests with a call to bind().
The client connects to the server by calling socket() then connect() with a socket address that includes the IP address and TCP port specifying used for the bind() call on the server. In most servers connections are accepted in one thread and a new thread or process is created to handle each connection. TCPAcceptor - Encapsulates the socket mechanisms to passively accept connections from a client. The constructor stores the connected socket descriptor then converts the socket information structure fields to a peer IP address string and peer TCP port. TCPConnector provides the connect() method to actively establish a connection with a server. The TCPConnector class does not use any member variables so the default constructor and destructor generated by the C++ compiler are fine.
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In a newsroom environments, all the information for an article is often not sent in one batch.
In addition, other information may have been entered by Editors the night before or later on. One requirement of this system is that data be pre-formatted to the simple XML format prior to import.
For example, Cofax, as implemented in Philadelphia, utilizes a SQL Data Store class that allows you to use any suitable database with a JDBC driver. The Presentation Layer named by its function: That is to provide the information to the Application layer and its also responsible for information conversion and code formatting. The Presentation Layer is basically a decoder or interpreter and offers coding and decoding functions.
Many other tasks, such as compression, decompression, encryption, and decryption are also related with the presentation layer and some standard of this layer are also engrossed in the multimedia operations. I’ve knowledge in web design, communication design, skills with Adobe Photoshop and the photomanipulation process. I like to design everything, but most of all I like to provide tools for professional designers like me.
This layer includes controls for user input and display, in addition to components that organize user interaction.
Choose a client type that satisfies your requirements and adheres to the infrastructure and deployment constraints of your organization.
Choose the data format for your presentation layer and decide how you will present the data in your UI. If your application has multiple layers, such as a data access layer and a business layer, determine a strategy for communication between your presentation layer and other layers.
Determine if you will implement a rich (smart) client, a Web client, or a rich Internet application (RIA). Review the presentation layer patterns for proven solutions to common presentation problems. Composition patterns support the creation of views and the presentation layout at run time.
For example, use the Template View pattern to compose dynamic Web pages in order to ensure reuse and consistency. For example, use the Composite View pattern to build a view from modular, atomic component parts.
Pay particular attention to exceptions that propagate across layer or tier boundaries, as well as exceptions that cross trust boundaries.
In the case of business errors, display a user-friendly error message and allow the user to retry the operation. For maximum usability, follow the established guidelines defined in your organization, and the many established industry usability guidelines based on years of user research into input design and mechanisms.
You should consider users with disabilities when designing your input strategy; for example, implement text-to-speech software for blind users, or enlarge text and images for users with poor sight. When choosing a layout strategy, consider whether you will have a separate team of designers building the layout, or whether the development team will create the UI.
For example, with touch-screen input you will typically use larger buttons with more spacing between them than you would with mouse or keyboard inputs. Ensure that you display navigation links and controls in a consistent way throughout your application to reduce user confusion and hide application complexity. Presentation entities are not always necessary; use them only if your datasets are sufficiently large and complex to require separate storage from the UI controls.
Typically, you may require presentation entities only if the data or the format to be displayed is specific to the presentation layer.
Carry out usability studies, surveys, and interviews to understand what users require and expect from your application, and design with these results in mind. Allow the user to control how he or she interacts with the application, and how it displays data to them.
Be careful not to create custom controls unless it is necessary for specialized display or data collection.
UI processing components are not always necessary; create them only if you need to perform significant processing in the presentation layer that must be separated from the UI controls. Determine the validation rules for user input as well as for business rules that exist in the presentation layer.
Always use server-side validation to constrain input for security purposes and to make security-related decisions. Execute long-running tasks on a separate thread that executes in the background, and provide a function for the thread to call back into when the task is complete. Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Encapsulate request processing in a separate command object with a common execution interface.
An object that transforms message data types into business types for requests, and reverses the transformation for responses. Prevent a service from exposing information about its internal implementation when an exception occurs. Consolidate request handling by channeling all requests through a single handler object, which can be modified at run time with decorators. Separate the UI code into three separate units: Model (data), View (interface), and Presenter (processing logic), with a focus on the View. Improve the response time for dynamic Web pages that are accessed frequently but change less often and consume a large amount of system resources to construct. Reduce the view to the absolute minimum by allowing the controller to process user input and maintain the responsibility for updating the view.
Move all view logic and state out of the view, and render the view through data-binding and templates.


A variation of the MVC pattern in which the controller handles complex logic, in particular coordinating between views, but the view is responsible for simple view-specific logic. Transform the model data into a logical presentation without any specific formatting, and then convert that logical presentation to add the actual formatting required.
The guidelines also contain suggestions for common patterns that are useful for specific types of application and technology. By thinking in terms of design patterns, we can devise abstractions for creating connections and transferring data between network peers that encapsulate socket calls in easy to use C++ classes. Network drivers are implemented here that provide the Network layer with the means to send packets over physical network media such as Ethernet, PPP and ADSL. The Network layer in the Internet model provides connectionless Internet protocol packet delivery, host IP addresses and routing hosts and other networks. TCP provides connection based, reliable network communication and stream based data delivery services. Calling listen() puts the server into listening mode which then blocks on the accept() waiting for incoming connections. On the server the accept() function returns with a connection socket descriptor when the client’s connection request is received.
The client calls write() to send a request then blocks on a call to read() waiting for the server’s response. To keep things simple the example here describes an iterative server where each request is handled one at a time. This is a factory class which produces TCPStream objects when client applications establish connections with servers. You can get the same information from the sockets getpeername() function but it far easier to just capture that information when the connections are established. The server struct sockaddr_in sin_family is set to PF_INET and the sin_port is set to the TCP port on which the server is listening for connections. If this call fails the assumption is made the server string contains an IP address and it is converted to an IP address in network byte order. If inet_ntop() fails then the socket listening address is set to any IP address meaning the server will listening for connections on all the network interfaces. To disable this condition and make it possible to immediately resue a listening port, we set the SO_REUSEADDR socket option for the listening socket before calling bind(). To keep things simple we’ll just make an iterative server that handles one connection at a time. If the number of arguments is not correct an error message is displayed informing the user how to correctly invoke the application. Processing consists of getting a string of bytes from the client, displaying the string and returning it to the client. The basic article with basic meta data from the publishing system may come from one source in a batch feed or in real time.
For example, from an automatic AI categorization engine like autonomy which may take a while to process the feed. Once Cofax has imported the data, it is immediately available for delivery to a variety of clients ranging from web browsers via a web application server to export feeds to other systems. Using WSIWYG Templates, a designer can "view source" a live page, static or dynamic, make changes, ensure that the comment tags are in place and the template is immediately usable.
An unbeaten data transport methods is to convert the data into a typical design before communication.
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For instance, if your users are on mobile devices and will be intermittently connected to the network, a mobile rich client is probably your best choice.
Base your decision on application requirements, and on organizational and infrastructure constraints.
Review established UI guidelines based on the client type and technologies that you have chosen.
Use surveys, usability studies, and interviews to determine the best presentation design to meet your customer’s requirements. The following table lists the common issues for each category where mistakes are most often made. Cache the results of expensive or repetitive processes to avoid unnecessary duplicate processing. These patterns also help to minimize code and library dependencies that would otherwise force recompilation and redeployment of a module when the dependencies change.
Design for unhandled exceptions so they do not impact application reliability or expose sensitive information.
In the case of system exceptions, check to see if the exception was caused by issues such as system or database failure, display a user-friendly error message, and log the error message, which will help in troubleshooting. Support keyboard-only scenarios where possible for users who cannot manipulate a pointing device. If designers will be creating the UI, choose a layout approach that does not require code or the use of development-focused tools.
Be careful not to mix business and display logic within the process components; they should be focused on organizing user interactions with your UI. Two variations on this pattern include Passive View and Supervising Controller, which define how the View interacts with the Model. TCPStream includes simple get methods that return address and port, but not the socket descriptor which is kept private. The string of bytes is NULL terminated at the index in the receive buffer equal to the value returned by the receive operation. The very simple article dtd is used for this since most newsprint publishing systems have only this information. Computers are configured to receive this typically designed data and then adapt the data back into its resident design for genuine reading for example EBCDIC to ASCII. Implementing common user interaction patterns as separate user process components allows you to reuse them in multiple UIs. Composition patterns help you to implement sharing, reuse, and replacement of presentation logic and views. UDP provides connectionless and packet based delivery where the data is delivered in datagrams  – packets with port numbers. The exchange of requests and responses repeats until the client is done, at which time it closes the connection.
One of the advantages of programming with objects is the ability to logically group data members and methods to avoid exposing data, in this case the socket descriptor, to the calling program that it does not need to see. In both cases the socket address information is passed to the TCPStream object when it is constructed. The Presentation Layer makes sure that information transmission with the Application layer of a computer can be accessed by the Application layer of another computer because of translation services. UDP, like IP, gives only best effort data delivery without retransmissions of dropped packets. The server responds by closing its end of the connection then returning to get another connection.



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