.NET/Java PDF, Tiff, Barcode SDK Library

If you need to control the network interactions on a lower level, Qt provides classes for sockets based on TCP and UDP Although the differences between these two are many and outside the scope of this book, each can be greatly simplified: TCP is good for establishing a session between two computers and transmitting data between them in a reliable way The data is transmitted as a stream UDP is good for sending individual packages of data between computers The sender does not need to know whether a receiver is receiving, and the receiver does not know if it has received all the data sent The data is transmitted as individual independent packages called datagrams When implementing a TCP server, you can inherit from the QTcpServer class Simply re-implement the incomingConnection to handle new connections The integer argument given is a socket descriptor.

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}; return customers;

LastName = "Shilts", EmailAddress = "rShilts@foo.com"}, new Customer {FirstName = "Michelangelo", LastName = "Signorile ", EmailAddress = "mSignorile@foo.com"}, new Customer {FirstName = "Larry", LastName = "Kramer", EmailAddress = "lKramer@foo.com"}, new Customer {FirstName = "Jennifer", LastName = "Baumgardner", EmailAddress = "jBaumgardner@foo.com"}

static void Main() { XDocument customerXml = CreateCustomerListXml(); Console.WriteLine("Search for single element..."); var query = from customer in customerXml.Element("Customers").Elements("Customer") where customer.Attribute("FirstName").Value == "Douglas" select customer; XElement oneCustomer = query.SingleOrDefault(); if (oneCustomer != null) { Console.WriteLine(oneCustomer); } else { Console.WriteLine("Not found"); } Console.WriteLine("\nSearch using descendant axis... "); query = from customer in customerXml.Descendants("Customer") where customer.Attribute("FirstName").Value == "Douglas" select customer; oneCustomer = query.SingleOrDefault(); if (oneCustomer != null) { Console.WriteLine(oneCustomer); } else { Console.WriteLine("Not found"); } Console.WriteLine("\nSearch using element values... "); query = from emailAddress in customerXml.Descendants("EmailAddress") where emailAddress.Value == "dAdams@foo.com"

Pass this to the constructor of the QTcpSocket class to get a socket connected to the incoming connection To set up the server to listen to a port, use the listen method By specifying QHostAddress::Any as host address, the server will accept all incoming connections A QTcpSocket is used both by the server created from the socket descriptor and the client In the client, you use the connectToHost to specify the server and port to connect to Because the QTcpSocket inherits from the QIODevice class, you can set up a QDataStream (or QTextStream) to send and receive data over the connection it represents When implementing a UDP server, start by creating a QUdpSocket You can then write to the socket using writeDatagram When implementing a client, use the same class, QUdpSocket, but bind it to a port by using bind.

select emailAddress; XElement oneEmail = query.SingleOrDefault(); if (oneEmail != null) { Console.WriteLine(oneEmail); } else { Console.WriteLine("Not found"); } Console.WriteLine("\nSearch using child element values... "); query = from customer in customerXml.Descendants("Customer") where customer.Element("EmailAddress").Value == "dAdams@foo.com" select customer; oneCustomer = query.SingleOrDefault(); if (oneCustomer != null) { Console.WriteLine(oneCustomer); } else { Console.WriteLine("Not found"); } } } // end main // end class // end namespace

}

As you can see in Figure 11-8, the application uses two UpdatePanel controls. Each of these contains a label. Each has an associated UpdateProgress control. The ScriptManager control on the page has Enable Partial Rendering set to true, meaning that updates to these UpdatePanel controls will not incur a full-page refresh. Finally, a timer control on the left triggers a timed update to the basic quote information every minute. Listing 11-1 shows the markup for these controls. Listing 11-1. Markup for the UpdatePanel Controls <table width="100%" cellpadding="2" style="border-width: 0"> <tr> <td style="width: 117px" class="style1"> <strong>Stock Ticker</strong> </td> <td style="width: 133px"> <asp:TextBox ID="TextBox1" runat="server" OnTextChanged="TextBox1_TextChanged">MSFT </asp:TextBox> </td> <td class="style1" style="width: 289px"> <strong> <atlas:UpdatePanel ID="UpdatePanel3" runat="server"> <ContentTemplate>

Output: Search for single element... <Customer FirstName="Douglas" LastName="Adams"> <EmailAddress>dAdams@foo.com</EmailAddress> </Customer> Search using descendant axis... <Customer FirstName="Douglas" LastName="Adams"> <EmailAddress>dAdams@foo.com</EmailAddress> </Customer> Search using element values... <EmailAddress>dAdams@foo.com</EmailAddress> Search using child element values... <Customer FirstName="Douglas" LastName="Adams"> <EmailAddress>dAdams@foo.com</EmailAddress> </Customer>

This example refactors Example 12-3 by extracting the creation of the sample customer list XML document into the CreateCustomerListXml() method. You can now simply call this function in the Main() function to create the XML document.

Each time a datagram arrives to the port that the socket is bound to, it emits a readyRead signal You can then read the datagram using readDatagram..

C# has a set of rules for working out the order in which to evaluate the components of an expression. It does not necessarily work from left to right, because some operators have a higher precedence than others. For example, imagine evaluating this: 1.0 + 3.0 / 4.0 from left to right. Start with 1.0, add 3.0 which gets you to 4.0, and then divide by 4.0 the result would be 1.0. But the conventional rules of arithmetic mean the result should be one and three quarters. And that s just what C# produces the result is 1.75. The division is performed before the addition, because division has higher precedence than division. Some groups of operators have equal precedence. For example, multiplication and division have equal precedence. When expressions contain multiple operations with the same precedence, mathematical operations are evaluated from left to right. So 10.0 / 2.0 * 5.0 evaluates to 25.0. But parentheses trump precedence, so 10.0 / (2.0 * 5.0) evaluates to 1.0. Some programming books go into great depths about all the details of precedence, but it makes for exceptionally tedious reading C# has 15 different levels of precedence. The details are important for compiler writers, but of limited value for developers code that relies heavily on precedence can be hard to read. Using parentheses to make evaluation order explicit can often improve clarity. But if you would like the gory details, you can find them at http://msdn.microsoft.com/en-us/library/aa691323.