Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

As a result, the page first executes the client-side script associated with the HTMLbutton and fills the control with the XML data. Next the browser posts the page back tothe server as the submit button type mandates. This behavior is undesired for a coupleof reasons. First, it produces an unneeded round-trip to the Web server. Second, theround-trip cancels the changes to the user interface that have been made on the clientand that constitute the core of our efforts and our main reason for building and using amanaged control. On the other hand, the Windows Forms control is not a server-sidecontrol and does not have access to the ViewState property to control its state whenthe page posts back.This problem has a simple workaround: don't use the tag to insert abutton that is expected to interact with the managed control through client-side scriptcode. Instead, use the tag and explicitly set the type attribute to button, asshown in the following code:Also, don't set the runat attribute; if you do, the onclick attribute will be mistaken forserver-side code to be executed. In this way, the browser executes the associatedclient-side script code and refreshes the page accordingly, but no postback occurs.Using Hidden Fields and SQL QueriesDespite the fact that the tag is the official way of defining XML data islands withInternet Explorer, a hidden field is probably a better solution. With a hidden field,Internet Explorer doesn't preprocess the XML data into a COM-based XML DOMobject. This feature is welcome if you are going to process the XML data using scriptcode. No parsing is needed if you only plan to pass the XML data island to a managedcontrol, however. Using a hidden field or a hidden tag is a valid approach to insertingXML data in the body of an HTML page.The following code illustrates how to create a hidden field that contains dynamicallygenerated XML data. The data is the output you get from the XML normal form of aDataSet object. In this sample code, the DataSet object is obtained by running a queryagainst the Customers table in the Northwind database.private void Page_Load(object sender, EventArgs e){if (!IsPostBack){string xmldata = GetDataAsXml();RegisterHiddenField("xml", xmldata);}}private string GetDataAsXml(){SqlDataAdapter adapter = new SqlDataAdapter("SELECT customerid, companyname, contactname,contacttitle, city, country FROM customers",501