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Say that we have a browser-enabled form template where we sink every available data source and form event Then we ll out the form side by side in InfoPath and the browser How does the behavior of the form in InfoPath compare to that in the browser You may be pleased to know that the experience is very similar in almost every respect Of course, this is what you d expect with design once: Write the same code once and it works in both InfoPath and Forms Services Although the parity between the platforms exists, the browser reacts differently in response to data source events The browser is lazy compared to InfoPath Let s see what this means To better understand the difference between InfoPath and Forms Services with respect to data source events, let s take a very simple example Say that we create a form template with a single Text Box (bound to eld1) Then we de ne an event handler for eld1 to listen to either the Validating or Changed event; it doesn t matter Do something in that event handler so you know when it runs such as setting eld1 to "Hello, InfoPath!" Now ll out that form by editing the Text Box in both InfoPath and the browser In InfoPath, you ll notice that the Text Box will immediately show "Hello, InfoPath!" after you click or tab away What happens in the browser Unlike InfoPath, the Text Box doesn t change after an edit! Forms Services, by default, does not automatically run form code on demand Its behavior is such, as we ll see toward the end
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17: Advanced Forms Ser vice s
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of this chapter, for performance motivations The form code for data source events is run only when data is sent to the server on a postback Later in the chapter, you ll learn more about how the server gets the form data from the browser on a postback As you can see, sinking data source events, such as Validating or Changed, does not re event handler code immediately after the data is changed To make this happen in the browser exactly as it does in InfoPath, you ll need to con gure the control s Postback settings option on the Browser forms tab (for the control bound to the data source listening to data source events) to Always Then the control will always post back whenever the value changes (refer back to Figure 173)
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Performance Issues with Extra Postbacks
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There is a ne balance between form correctness and performance The more postbacks your form makes during lling, the fewer overall number of concurrent users and forms your server will be able to adequately serve We look more closely at server and browser performance at the end of the chapter
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Circumventing Browser-Enabled Limitations Almost everything you learned about programming InfoPath in 15 applies to Forms Services There are some exceptions, however One of the biggest exceptions in browser-enabled forms is the lack of UI through rules and form code (The exception to not showing UI in the browser is the submit feature, where standard or custom submit messages show an alert dialog in the browser)
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One sorely missed feature of InfoPath in the browser is the ability to show a message box Since the SystemWindowsFormsdll assembly isn t referenced, the MessageBoxShow() method is unavailable (and even if it was, showing UI is suppressed) Despite the inability to show UI in the browser, it doesn t mean we can t do something similar! With a little creativity, we re able to simulate showing a message box in a browser-based form Figure 177 shows our own dialog box (See the sample called MessageBox)
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