how to create qr code using vb.net INTRODUCING THE .N ET M IC RO FRA MEWORK BA SE CLA SS LIBRA RY in visual basic

Include QR Code JIS X 0510 in visual basic INTRODUCING THE .N ET M IC RO FRA MEWORK BA SE CLA SS LIBRA RY

We used a variety of techniques during the design and implementation phases when building Postage; these allowed us to leverage the design concepts we have discussed so far to create the final polished application. Some of the same tools and methods we applied will undoubtedly help you create an outstanding application of your own.

// Create a list box control and add text items ListBox listBox = new ListBox(); for (int i = 0; i < 10; ++i) { string str = "Item " + i.ToString() + ". Hello World."; listBox.Items.Add(new Text(font, str)); } // Add the text control to the window. mainWindow.Child = listBox; // Set the window visibility to visible. mainWindow.Visibility = Visibility.Visible; // Let the user select items with the up and down buttons. Buttons.Focus(listBox); // Get notified when the selected item was changed. listBox.SelectionChanged += new SelectionChangedEventHandler(listBox_SelectionChanged); // Get notified when a selected item was pressed // using the select button. listBox.AddHandler(Buttons.ButtonDownEvent, new ButtonEventHandler(listBox_ButtonDown), false); return mainWindow; } private void listBox_SelectionChanged(object sender, SelectionChangedEventArgs args) { Debug.Print("Item " + args.SelectedIndex + " was selected."); } private void listBox_ButtonDown(object sender, ButtonEventArgs args) { ListBox listBox = (ListBox)sender; if(args.Button == Button.Select) Debug.Print("Item " + listBox.SelectedIndex + " was pressed."); } } } Figure 11-38 show the text list box. The code in Listing 11-28 has one big drawback: you will not see which item was selected on the screen. Therefore, you need to change the visual appearance of the selected item to indicate the current item to the user; we ll discuss how in the next section.

Figure 5-7. Invoking GetAllTitle using Async callback Here you may wonder which mechanism to choose subscribing to the completed event or using the Async callback. It very much depends upon your needs. Asynchronous callbacks are very similar to events in terms of what they do. They both provide a mechanism for one piece of code to say to another, Do this job and when you are done, let me know. The difference here is that with a completed event, many pieces of code can be notified when the event occurs, whereas with an Async callback, only the caller can be notified. This is because essentially an event is a wrapper around a set of callbacks. You use the += operator to subscribe to the callback that is, in turn, the event handler onto the event object. The event class handles the work of invoking all the subscribed callbacks when the event is raised. But a method that takes an explicit callback parameter (such as BeginInvoke in our previous example) doesn t support any mechanism for handling a set of callbacks. They remember only the callback that was passed to them as a parameter (Async callback GetAllTitle in our case), and then invoke that when they re finished. So to be straight, use Async callbacks if you need to notify only the code that called of completion, and use Events for a multi-threading scenario in which you want to enable more than one piece of code to be notified.

Figure 2-3. Class diagram showing a more complex set of class relationships Now things get even more complicated. If the user edits a Component object, the changes ultimately impact the state of the Invoice object itself. Of course, changing a Component also changes the state of the LineItem object that owns the Component. The user might accept changes to a Component but cancel the changes to its parent LineItem object, thereby forcing an undo operation to reverse accepted changes to the Component. Or in an even more complex scenario, the user may accept the changes to a Component and its parent LineItem only to cancel the Invoice. This would force an undo operation that reverses all those changes to the child objects. Implementing an undo mechanism to support such n-level scenarios isn t trivial. The application must implement code to take a snapshot of the state of each object before it s edited so that changes can be reversed later on. The application might even need to take more than one snapshot of an object s state at different points in the editing process so that the object can revert to the appropriate point, based on when the user chooses to accept or cancel any edits.

Remember that all Web service specifications are composable. Routing does not implement any kind of security for referred messages. However, you can use WS-Security in conjunction with routing to provide a security solution for the referred messages. For example, you can digitally sign or encrypt incoming messages, as you saw in the SOAPSender solution. Note that encrypted messages can pass through intermediary routers even if those routers do not know how to decrypt the message. Routing configuration is separate from the message contents. The intermediary only needs to decrypt the message if this is required in order to make a specialized routing decision. But in most cases this will not be necessary. If the routers do need to decrypt the message and you use X.509 certificates for encryption, you must ensure that each of the intermediary services has access to the necessary keys. In fact, this applies whenever you use an X.509 certificate, whether for digital signatures or encryption. In a chain routing model, it is likely that intermediary services will modify the contents of an incoming SOAP request message. If the incoming SOAP message is digitally signed, the intermediary service will need to re-sign the message before forwarding it on to the next service. However, as the SOAPSender solution shows you, digital signature validation will not fail if the SOAP router simply passes on the SOAP message to a destination endpoint without altering the message contents. There is no question that routing solutions add an administrative and development burden to implementing an SOA. And when you add security policies into the mix, the burden will become even greater. It is likely that future releases of WSE will include provisions to address this issue. To this date, subsequent releases of WSE have always managed to reduce complexity compared to earlier releases of the same features.

Note For excellent discussions of the general structure of .NET and its components, see Introducing