create a qr code using c# and asp.net Part V in Visual C#.NET

Generation QR Code in Visual C#.NET Part V

Part V
Making QR-Code In Visual C#.NET
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Quick Response Code Reader In C#
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The Client Side
Draw Bar Code In Visual C#
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Recognize Barcode In Visual C#
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Scriptable Services
Quick Response Code Creation In .NET Framework
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QR-Code Drawer In VS .NET
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Any Ajax solution is made of two main layers that are neatly separated but communicating: the JavaScript and HTML presentation layer, and a service layer that acts as a fa ade for HTTP endpoints. Figure 20-4 gives an overview of the architecture.
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Data Matrix ECC200 Creation In C#.NET
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Browser
GS1-128 Drawer In Visual C#
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PDF 417 Generation In C#.NET
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JavaScript and HTML
Encoding UPC-A Supplement 2 In C#
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USD8 Maker In C#.NET
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Roundtrip
UCC.EAN - 128 Creation In None
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Encoding UPC-A Supplement 2 In None
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Internet
Reading EAN 13 In Visual C#.NET
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Linear Barcode Generator In Java
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HTTP Facade Local/Internet
Generating UPC Code In None
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QR Code ISO/IEC18004 Creator In Objective-C
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Rest of the system (Business layer, DAL)
Encode Bar Code In Java
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Scanning Barcode In Java
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FIGURE 20-4 A typical Ajax architecture.
The HTTP fa ade works out a convenient API for the presentation layer to call. The API is built on top of the existing application services and workflows. The HTTP fa ade scripts these middle-tier components from the client. The architectural relevance of the HTTP fa ade is that it decouples the middle tier from a special presentation layer, such as an Ajax presentation layer. An Ajax presentation layer is special essentially because it s a partial-trust Web client. For security reasons, service technologies hosted on the Web server require special adjustments to enable JavaScript callers. In addition, it s likely that some of the application services you have in the middle tier run critical procedures. Any piece of code bound to a URL in the HTTP fa ade, instead, is publicly exposed over the Internet not an ideal situation for a business-critical service. So decoupling application services from the Ajax presentation layer is a measure of design but also a matter of security. How would you build the HTTP fa ade
20 Ajax Programming
The HTTP Fa ade
The HTTP fa ade is the list of public URLs known to, and managed by, the Ajax presentation layer. In an Ajax scenario, the presentation layer is made of only JavaScript code. All the logic you can t or don t want to code in JavaScript must be referenced on the server. Public HTTP endpoints are the only point of contact between Ajax clients and server applications. You can write endpoints callable by Ajax clients using a number of technologies. Note In the context of Ajax, Web-hosted services are instrumental to the definition of a public, contract-based API that JavaScript code can invoke. It doesn t mean that you can call just any public Web services from an Ajax client. More precisely, you can call only services that live in the same domain as the calling page in full respect of the Same Origin Policy (SOP) implemented by most browsers. This is a security measure, not a technical limitation. You should think of Web services as a sort of application-specific fa ade to expose some server-side logic to a JavaScript (or Silverlight) client. To start off, an AJAX-callable endpoint can be an .asmx ASP.NET Web service. If this is your choice, you need to configure the server ASP.NET application so that its hosted Web services can accept JSON calls in addition to, or instead of, SOAP calls. You can also use a Windows Communication Foundation (WCF) service to contain all the logic you want to expose to Ajax clients. As you ll see later in the chapter, though, you get only the Web WCF programming interface and, as such, only a subset of the typical WCF features. In particular, the area of security is thinned down. A common solution for ASP.NET Web Forms Ajax-enabled applications is hosting WCF services and interacting with them via JSON payloads. If you don t want to add WCF to your application but still need a service, you can then opt for a custom, handmade HTTP handler. An HTTP handler is just a public URL exposed by a Web application, so it can reliably serve any purpose the presentation needs to address. Compared to WCF services, plain HTTP handlers lack a lot of facilities, including the automatic JSON serialization of input and output data. (You can use the same tools that WCF uses, but that s just not automatic.)
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