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Simple .NET/ASP.NET PDF document editor web control SDKThat s all very well, but we don t actually want that restriction the fire chief should be allowed to pass the work off to his subordinate as often as he likes, regardless of who he asked to do it. create barcode excel 2013, barcode excel 2003 free download, barcode add in for excel 2013, barcode generator in excel 2007 free download, excel formula to generate 12 digit barcode check digit, barcode erstellen excel freeware, barcode excel 2013 download, how to create barcode in microsoft excel 2007, barcode erstellen excel, formula to create barcode in excel 2010,There s one big caveat regarding everything we ve just shown about method hiding: I can t think of the last time I used this feature in a real application, but I see the warning from time to time and it usually alerts me to a mistake in my code. We ve wanted to illustrate how method hiding works, but we discourage you from using it. The main reason to avoid method hiding with new is that it tends to surprise your clients, and that, as we ve established, is not a good thing. (Would you really expect behavior to change because the type of the variable, not the underlying object, changes ) While method hiding is absolutely necessary for some corner cases, we usually treat this warning as an error, and think very carefully about what we re doing if it comes up. 9 times out of 10, we ve got an inadvertent clash of names. <html xmlns="http://www.w3.org/1999/xhtml" > <head><title> Untitled Page </title></head> <body> <form name="aspnetForm" method="post" action="Default3.aspx" id="aspnetForm"> <div> <input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPDwUKLTc4NzcwODI3NmRk9YXV49GLEVNvGzvlq/8dm4TNJOg=" /> </div> <script src="ScriptLibrary/Atlas/Debug/Atlas.js" type="text/javascript"></script> <div> This is the Master Page.<br /> It contains this ScriptManager control:<br /> <br /> </div> <script type="text/xml-script"> <page xmlns:script="http://schemas.microsoft.com/xml-script/2005"> <references> <add src="ScriptLibrary/Atlas/Debug/AtlasUIDragDrop.js" /> </references> <components /> </page></script> <script type="text/javascript"> </script> </form> </body> </html> What we actually want to do is to change the implementation based on the type of the object itself, not the variable we re using to get at it. To do that we need to replace or override the default implementation in our base class with the one in our derived class. A quick glance at the C# spec shows us that there is a keyword to let us do just that: override. Let s switch to the override modifier on the FireChief implementation of the ExtinguishFire() method: public override void ExtinguishFire() { // Get our number one to put out the fire instead TellFirefighterToExtinguishFire(NumberOne); } Figure 7-24. Mixing up the order of the translations rotates around the wrong origin. The order of translations is important for all translations. Both scaling and shearing are equally dependent on the origin of the coordinate system, just as rotating is. Notice that we removed the new modifier and replaced it with override instead. But if you compile, you ll see that we re not quite done (i.e., we get a compiler error): 'FireChief.ExtinguishFire()': cannot override inherited member 'Firefighter.ExtinguishFire()' because it is not marked virtual, abstract, or override We re not allowed to override the method with our own implementation because our base class has to say we re allowed to do so. Fortunately, we wrote the base class, so we can do that (as the compiler error suggests) by marking the method in the base with the virtual modifier: Figure 1-3. The connections between a, b, and c The following line shows a call to one of the objects: b->setText( "test" ); Try tracing the call from b, where there is a change from "bar" to "test"; through the connection to c, where there is a change from "baz" to "test"; and through the connection to b, class Firefighter { public virtual void ExtinguishFire() { Console.WriteLine("{0} is putting out the fire!", Name); } } // ... Why do we have this base-classes-opt-in system Why is everything not virtual by default (like, say, Java) Arguments continue on this very issue, but the designers of C# chose to go with the nonvirtual-by-default option. There are a couple of reasons for this: one has to do with implicit contracts, and another is related to versioning. In typical ASP.NET 2.0 applications, if you do a postback on the web page, the entire page will be rerendered. This causes a blink or a flash in the client or browser. On the server, the postback is detected, which triggers the page life cycle. This ends up raising the specific postback event handler code for the control that caused the postback, and this calls upon the page s event handler. When you use UpdatePanel controls along with a ScriptManager control, you eliminate the need for a full-page refresh. The UpdatePanel control is similar to a ContentPanel control in that it marks out a region on the web page that will automatically be updated when the postback occurs (but without the aforementioned postback behavior on the client). It will instead communicate through the XMLHttpRequest channel in true Ajax style. The page on the server still handles the postback as expected and executes, raising event handlers, and so on, but the final rendering of the page means that only the regions specified in the UpdatePanel control s regions will be created. There is also (potentially) a small performance overhead for virtual function dispatch, but this is negligible in most real-world scenarios. As always, test before optimizing for this!
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