15: Writing Code in InfoPath in .NET framework

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15: Writing Code in InfoPath
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Listing 157: Initializing FormState with UserIsAuthorized as false
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public void FormEvents_Loading(object sender, LoadingEventArgs e) { FormStateAdd(UserIsAuthorizedStr, false); }
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An ef cient and organized approach to use the FormState object is to expose it by wrapping it as a property This is exactly what we did with UserIsAuthorized As a property implementation, UserIsAuthorized appears to be a simple class-wide variable when you use it throughout your code Another advantage is that the dictionary aspects of the FormState object are abstracted away As a result, we recommend using properties (with set and get accessors) only to manage any name-value pairs stored in FormState
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Why not just use class-wide variables to store state Browser-enabled form templates do not allow the use of class-scoped variables Similar to an ASPNET page or Web service, Forms Services form code does not persist state between client HTTP requests The FormState object is the only way for browser-enabled templates to persist data for the duration of a given session
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Let s continue to study the code behind the myFields Changing event After verifying the correct password and setting UserIsAuthorized to true, the code calls MessageBoxShow as positive visual feedback to the user that he or she is authorized What happens if, instead, the user enters the wrong password or clicks Cancel The code that s executed includes the else block of the myFields_Changing event code shown earlier in Listing 155 This code represents the essence of the Changing event Of the three XML events, this is the only time when modi cation to node data can be rejected If we do not cancel the Changing event, the change to the data will undoubtedly occur Setting the CancelableArgsCancel property (from
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The InfoPath Obje ct Model
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the XmlChangingEventArgs variable e) to true will, after the Changing event handler has nished, cause InfoPath to reject the change of node data Canceling the Changing event will kill all subsequent noti cations for this node, so the Validating and Changed events will not re If the Message and/or MessageDetails properties are assigned, they are used in an error dialog that signi es the change was rejected If at least the Message property is not set before the event handler returns, the default message is shown: Invalid update: A custom constraint has been violated As a courtesy to your users, you should consider providing a more informative message, such as we did for the MoiEventScheduler-Changing sample (Figure 159)
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Figure 159: Custom error message that appears when a Changing event handler is canceled
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Only Changing Is Cancelable
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The Changing event is the only XML event that can be canceled Canceling the Changing event suppresses the data change from propagating to the Validating and Changed events Many form events are also cancelable if the event s argument inherits from the CancelEventArgs NET Framework class
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Once an authorized user enters the correct password and lls out the form, the last step is to click the Send to HR for Approval button, which sends e-mail to the morale contacts in the human resources department
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15: Writing Code in InfoPath
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Clicking the Send to HR for Approval button will not re the myFields event handler, nor will it re any event handler that we have set up As a result, the submission is allowed even though the user doesn t have access and the form is empty To x this bug with our form, we can conditionally disable the button while the Event title eld is empty (Event title is convenient to use, although any eld or combination of elds could have been used instead) Later in this chapter, we ll look at how to sink a Button click event so we could handle this in code if so desired
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You now have a good understanding of the Changing event Before we move on to the next XML event, you should know about a couple of general restrictions regarding the Changing event First, not all OM calls can be made from this event handler For example, switching views programmatically (which is covered later in this chapter) is disallowed If an invalid OM call is made in a Changing handler, InfoPath throws an exception, which automatically cancels the event This exception manifests itself to the user as a visual error (Figure 1510) A complete list of unsupported OM calls during XML events appears in Table 153 Another limitation of the Changing event is that the entire main data source is read-only Any changes to the data using an XPathNavigator (or any other means) will also throw an exception similar to the one shown in Figure 1510 The reasoning behind a read-only main data source is that the
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