how to generate qr code in asp.net using c# Object Types and dynamic in C#.NET

Maker QR Code in C#.NET Object Types and dynamic

Object Types and dynamic
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Not all objects behave in the same way when you use them through the dynamic keyword. C# distinguishes between three kinds of objects for dynamic purposes: COM objects, objects that choose to customize their dynamic behavior, and ordinary .NET objects. We ll see several examples of that second category, but we ll start by looking at the most important dynamic scenario: interop with COM objects.
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COM objects such as those offered by Microsoft Word or Excel get special handling from dynamic. It looks for COM automation support (i.e., an implementation of the IDispatch COM interface) and uses this to access methods and properties. Automation is designed to support runtime discovery of members, and it provides mechanisms for dealing with optional arguments, coercing argument types where necessary. The dynamic keyword defers to these services for all member access. Example 18-6 relies on this.
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static void Main(string[] args) { Type appType = Type.GetTypeFromProgID("Word.Application"); dynamic wordApp = Activator.CreateInstance(appType); dynamic doc = wordApp.Documents.Open("WordDoc.docx", ReadOnly:true); dynamic docProperties = doc.BuiltInDocumentProperties; string authorName = docProperties["Author"].Value; doc.Close(SaveChanges:false); Console.WriteLine(authorName);
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The first two lines in this method just create an instance of Word s application COM class. The line that calls wordApp.Documents.Open will end up using COM automation to retrieve the Document property from the application object, and then invoke the Open method on the document object. That method has 16 arguments, but dynamic uses the mechanisms provided by COM automation to offer only the two arguments the code has provided, letting Word provide defaults for all the rest. Although dynamic is doing some very COM-specific work here, the syntax looks like normal C#. That s because the compiler has no idea what s going on here it never does with dynamic. So the syntax looks the same regardless of what happens at runtime.
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If you are familiar with COM you will be aware that not all COM objects support automation. COM also supports custom interfaces, which do not support dynamic semantics they rely on compile-time knowledge to work at all. Since there is no general runtime mechanism for discovering what members a custom interface offers, dynamic is unsuitable for dealing with these kinds of COM interfaces. However, custom interfaces are well suited to the COM interop services described in 19. dynamic was added to C# mainly because of the problems specific to automation, so trying to use it with custom COM interfaces would be a case of the wrong tool for the job. dynamic is most likely to be useful for Windows applications that provide some sort of scripting feature because these normally use COM automation, particularly those that provide VBA as their default scripting language.
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Silverlight applications can run in the web browser, which adds an important interop scenario: interoperability between C# code and browser objects. Those might be objects from the DOM, or from script. In either case, these objects have characteristics that fit much better with dynamic than with normal C# syntax, because these objects decide which properties are available at runtime. Silverlight 3 used C# 3.0, so dynamic was not available. It was still possible to use objects from the browser scripting world, but the syntax was not quite as natural. For example, you might have defined a JavaScript function on a web page, such as the one shown in Example 18-7.
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<script type="text/javascript"> function showMessage(msg) { var msgDiv = document.getElementById("messagePlaceholder"); msgDiv.innerText = msg; } </script>
Before C# 4.0, you could invoke this in a couple of ways, both of which are illustrated in Example 18-8.
ScriptObject showMessage = (ScriptObject) HtmlPage.Window.GetProperty("showMessage"); showMessage.InvokeSelf("Hello, world"); // Or... ScriptObject window = HtmlPage.Window; window.Invoke("showMessage", "Hello, world");
While these techniques are significantly less horrid than the C# 3.0 code for COM automation, they are both a little cumbersome. We have to use helper methods GetProperty, InvokeSelf, or Invoke to retrieve properties and invoke functions. But Silverlight 4 supports C# 4.0, and all script objects can now be used through the dynamic keyword, as Example 18-9 shows.
dynamic window = HtmlPage.Window; window.showMessage("Hello, world");
This is a far more natural syntax, so much so that the second line of code happens to be valid JavaScript as well as being valid C#. (It s idiomatically unusual in a web page, the window object is the global object, and so you d normally leave it out, but you re certainly allowed to refer to it explicitly, so if you were to paste that last line into script in a web page, it would do the same thing as it does in C#.) So dynamic has given us the ability to use JavaScript objects in C# with a very similar syntax to what we d use in JavaScript itself it doesn t get much more straightforward than that.
The Visual Studio tools for Silverlight do not automatically add a reference to the support library that enables dynamic to work. So when you first add a dynamic variable to a Silverlight application, you ll get a compiler error. You need to add a reference to the Microsoft.CSharp library in your Silverlight project. This applies only to Silverlight projects other C# projects automatically have a reference to this library.
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