Software development

Chapter 5 – Data management

Contents ❷❸• Basics of data binding• Using online data• SQL databases• What is OData?• Assignments• Questions and answers

Need for data binding• The most simple method to display data on

screen is to display static data• This simple method is suitable for some

applications, such as e-readers or some simple games

• On a larger scale applications like these are not very versatile

Basics of data binding• Data binding is an essential method for

displaying data in Windows 8 applications• You can always write code that sets some

interface component to display data as programmed, in larger projects this might get troublesome

Data binding and XAML• Data binding can make two things less arduous

– Displaying data (from code to screen) – The situation where the user edits displayed data

through a component such as TextBox (from screen to code)

• Data binding is processed in the code through co-operation between classes and XAML strings

Startin point: C# class ”Student”public class Student{ public int Student ID { get; set; } public string Name { get; set; } public string Social security ID { get; set; } public string Email { get; set; }}

XAML definition• You need to know two things to write the

correct XAML definition1. Which source file property needs to be set as the

source2. Which property of which interface component

should be set as the destination• For example

– Student.Name --> TextBlock.Text

XAML syntax• You can recognize data binding processes in

XAML interfaces from the word Binding inside curly brackets { and }

• {Binding} definition is connected to that target component's property, which will be the destination of the data bond

Example<TextBlock x:Name="StudentIDTextBlock" Text="{Binding Student ID}" ... <TextBlock x:Name="NameTextBlock”Text="{Binding Name}" ...<TextBlock x:Name="SocialIDTextBlock" Text="{Binding Social security ID}" ...<TextBlock x:Name="EmailTextBlock" Text="{Binding Email}" ...

Defining data contents• Once the XAML data bond has been defined,

you must still tell the code which object instance the data bond will be connected to

• This is done by using the XAML page's DataContext property

Creating an object instance• Typically an object's data is fetched from a

data base, the Internet, or they are formed during processing

• You can also use static objects as an easy method to try how data binding works

ExampleStudent o = new Student(){ Student ID = 12345, Name = "Olli Opiskelija", Social security ID = "010290-123A", Email = "olli@oppilaitos.fi"};

Connecting the DataContext property

• You can connect any object to a page's DataContext property

• Data binding definitions in XAML will start looking for defined properties in the set object

• Example– this.DataContext = o;

Using online data• Your Windows 8 applications will come alive

after you connect them to online data• The online data feed can take many forms

– A Twitter feed, the day's news headlines in an RSS feed, or data produced by some background process in the XML format, etc.

Many possibilities• Windows 8 applications are capable of

versatile use of online data• Usually online data is fetched by using the

HTTP protocol– It is also possible to use socket or tcp/ip interfaces

or ftp

HttpClient class• A class titled HttpClient is available for Windows 8

applications– Found in the namespace Windows.Web.Http

• The class works asynchronously– The application will not stop and wait for the data to be

downloaded, but allows the user to continue using the application

• Supports also encrypted https protocol connections

ExampleHttpClient client = new HttpClient();Uri uri = new Uri("http://www.bing.com/");string data = await client.GetStringAsync(uri);

Application example: RSS reader• Let's look at a sample application that reads

the Yleisradio main news feed through an RSS feed– RSS = Really Simple Syndication

• Data can be downloaded with the HTTP protocol and data in RSS format is based on XML

Downloading RSS data with HTTPHttpClient client = new HttpClient();Uri uri = new Uri( "http://yle.fi/uutiset/rss/paauutiset.rss");string data = await client.GetStringAsync(uri);XmlDocument xml = new XmlDocument();xml.LoadXml(data);

RSS feed's title elements

Fetching titles from RSS feed• In the previous example the fetched RSS data

was input into an XML component• With this kind of component certain elements

can be found using the XML file's tree structure

Using an XML component• Finding title elements

– XmlNodeList nodes = xml.SelectNodes("//channel/item/title");

• Listing the contents of title elements, that is the news headlines– List<string> titles = nodes.Select(n =>

n.InnerText).ToList();

SQL databases• SQL is the most important query language especially for

database, which can be used to search for and update data in the database– Short for Structured Query Language

• SQL databases can be accessed in many ways– LAN databases typical, cloud-based SQL databases also widely used

• If an application is intended to be used• If the application is intended to be used outside an intranet, the

database connection is generally established through public Internet by using web technologies

Ways to access data

Web interfacesSocket connections

(tcp/ip)

Local installation Proxy server

SQL database

Options in a nutshell• The most simple option is to install the

database on the same device as the application

• The more common solution is to have a Windows 8 application access a separate server running the database over a network

Connection methods• Traditional LAN databases may require the use

of so called socket connections• More modern cloud-era databases allow

forming connections through HTTP• HTTP can also be used to access the database

through the Internet

OData• ODataor Open Data is a standard launched by

Microsoft and other IT operators• Odata can be used to transfer database data

(”SQL data”) over the Internet• The Odata standard is intended to work

especially with HTTP and XML and JSON data formats

OData platform support• Odata standard's newest version is 3.0• It is already supported by many different platforms

– The device itself is platform and device independent• Supported platforms include Windows, Mac OS X

and Linux• Applications supportin OData include Excel, PHP,

Ruby, and naturally Microsoft's .NET ja C# (and therefore Windows 8 applications)

Assignments• List at least three different methods to save data in a

Windows 8 application. What advantages and disadvantages does each method have?

• How can you build an application that are functional even when an Internet connection is not available?

• What advantages do open standards such as OData have for data transfer? What other data transfer standards can you name?

Questions and answers 1My application requires only simple data saving. What saving methods should I use?• For simple programs it can be enough to have a local XML file as a part of the

application. You can process XML files for example by using XmlDocument class, which is found in the namespace Windows.Data.Xml.Dom.

• You can also use some light SQL-based databases, such as SQLite. This database is easily introduced into your application with the so called NuGet package. You can find by using running a search for "SQLite for Windows Runtime" in Visual Studio.

• You might also want to take a look at the new Windows Azure Mobile Services, which can be used to quickly implement a web background system to your application

Questions and answers 2I'm developing a Windows 8 application and I'm writing my code using Visual Studio. The application should communicate with the background system by using the HTTP protocol. Do I have to use Visual Studio to also create the background system.• The advantage of open technologies (such as HTTP) is that that the used

development tools don't matter as long as standards are followed. Therefore your can write your Windows 8 application's interface in Visual Studio and the background system in Python or PHP if you so wish.

• There are, however, several advantages to writing also the background system in Visual Studio, as you don't need to use two development tools or more. Additionally, you can make use of efficient data transfer methods such as OData.

• You might want to familiarize yourself with Microsoft's ASP.NET technologies. They can be programmed in, for example, C#.

Questions and answers 3I've heard that many background systems have been attacked and account names and passwords have been stolen form them. How can I avoid such mistake?• This is a multifaceted, but important question. Especially the large background

systems and databases of popular applications are alluring targets to criminals.

• It is important that users' account names and passwords are appropriately encrypted. All encryption method are not equally good, and therefore you should carefully choose the most efficient encryption for your applications. Many other elements affect the security of background applications, and many books have been written on the subject.

• You can read more on the subject in, for example, "Building Secure ASP.NET Applications," which can be found on Microsoft's developer site at http://msdn.microsoft.com/en-us/library/ff649100.aspx.