Figure 9-3. Viewing a project in VB.NET

Painting PDF417 in VB.NET Figure 9-3. Viewing a project

Figure 9-3. Viewing a project
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The reason for this is that the user isn t logged in. This is clearly shown in the menu bar, which now has a Login button instead of a Logout button. To make this authorization behavior work, the main form must be able to notify all the loaded user controls when the current user logs in or out. That way, each user control can enable and disable its controls based on the authorization properties of the business object being edited by the form. The hard work is actually handled by the ReadWriteAuthorization control created in 5. Still, each user control must be notified about the fact that the user logged in or out so that the authorization code can be triggered. If the user has a number of documents open in the application, he can only see the one in front the active document. He could easily try to open the same document a second time, and this should result in the already open document being brought to the front to be the new active document. For instance, suppose the user opens project A. Then he opens some other projects and resources, so project A is no longer active. Then suppose the user again tries to open project A. In that case, the application won t open a new document rather, it will find the already open document for project A and will make it the active document. Finally, as the user interacts with a document, many things may happen, some of which can take a while. The user may load or save data, start a complex computing task, or any number of
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CHAPTER 9 s WINDOWS FORMS UI
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things that may take some time. When this happens, the main form s status bar should show text telling the user what is going on, and the mouse cursor should change to indicate that the application is busy. It is not good to write code in every user control to handle the details of the Documents menu. This code must detect login/logout activity, avoid duplicate documents, and display status to the user. That is all plumbing code that should be written once and reused by user controls. Although my intent with this chapter isn t to create a full-blown Windows Forms UI framework, these issues must be addressed for a basically decent user experience.
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The user will primarily interact with user controls hosted within the main form. In Visual Studio, each user control is really just like a regular form. Visual Studio even provides a user control designer surface, which you can use to create the user control just like you would normally create a form. In order to support the features discussed in the previous section, each user control needs some common functionality. To provide this functionality with the minimum amount of manual coding, the PTWin project includes a WinPart control. Each user control inherits from WinPart, rather than directly from UserControl. The WinPart base control implements behaviors common to all user controls that are to be hosted in the main form, including the following: Overrides for common System.Object methods Event notification for the process of closing Event notification when the current user s principal object is changed By inheriting from WinPart, a user control can often include no extra code beyond a simple GetIdValue() method, which must be implemented to return a unique identifier for the instance of the user control. In most cases, this method simply returns the business object being edited by the form. All other code in a typical user control centers around user interaction dealing with button clicks, text changes, and so forth.
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