Answers for Day 19 | Sams Teach Yourself ASP.NET in 21 Days (2nd Edition)


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	Sams Teach Yourself ASP.NET in 21 Days, Second Edition By Chris Payne
	Table of Contents

	Appendix A. Answers to Quiz Questions

Quiz

1:	True or false: A code-behind file must derive from the `System.Web.UI.Page` class.
A1:	True, unless the code-behind is for a user control, in which case it should derive from the `System.Web.UI.UserControl` class.
2:	Why must you declare public variables in a code-behind for the server controls you use on an ASP.NET page?
A1:	A code-behind file must programmatically control server controls that are located on a separate page; normally, this would be impossible. However, if you declare the controls in the code-behind and provide event handlers for them, ASP.NET can provide implementations for those controls. The ASP.NET page can use the controls declared in the code-behind because it derives from the code-behind. A code-behind declares and provides event handlers for server controls, whereas the ASP.NET page simply displays them.
3:	Create an `@ Page` directive that uses a code-behind class named `MyControl`, in a `.vb` file with the same name.
A1:	<%@ Page Inherits="MyControl" src="/books/4/226/1/html/2/MyControl.vb" %>
4:	What is a resource file?
A1:	It is a file that contains localizable values for an ASP.NET application.
5:	What does the following line do? dim strVar as string = Request.UserLanguages(0)
A1:	It retrieves the primary language of a user as indicated by her browser, and stores it in a string variable named `strVar`.
6:	What does the `resgen.exe` tool do?
A1:	It converts your text resource files into `.resources` files, which can be read by ASP.NET's resource manager.
7:	What is the difference between `CurrentCulture` and `CurrentUICulture`?
A1:	Both represent the culture used by an application, but the latter is used by ASP.NET to load resource files. The former is used by localizable objects, such as `DateTime`.
8:	True or false: The `CultureInfo.CurrentCulture` is a shortcut for the `System.Threading.CurrentThread.CurrentCulture` object.
A1:	True. The former is read-only, whereas the latter can be used to set culture information.

Exercise

Q1:

Create a currency exchange calculator for several different countries. Allow the user to enter a monetary value in one region's units, and convert to another by selecting a value from a select box. Use a resource file to store the exchange values. (Don't worry if you don't know the exchange rates, just make something up!) Use code-behind techniques!

A1:

This solution uses en-US, fr, de, and jp for the culture encodings. The resource files contain the conversion units for each culture. The file exchange.en-US.txt is as follows:

 Toen-US=1 Tofr=.7 Tode=1.67 Tojp=1098.45

The file exchange.fr-fr.txt is as follows:

 Toen-US=1.43 Tofr=1 Tode=2.34 Tojp=1569.21

The file exchange.jp-ja.txt is as follows:

 Toen-US=.0009 Tofr=.00064 Tode=.0015 Tojp=1

The file exchange.de-ge.txt is as follows:

 Toen-US=.59 Tofr=.42 Tode=1 Tojp=657.7

Don't forget to use resgen.exe to place these files in .resource files.

The user interface, exercise1.aspx, is as follows:

 1:    <%@ Page Inherits="ExchangeCalculator" src="/books/4/226/1/html/2/exercise1.vb" %> 2: 3:    <html><body> 4:       <font size="5">Currency Calculator</font><hr> 5:       <form runat="server"> 6:          <asp:Label  runat="server"/> 7:          <asp:TextBox  runat="server"/> to 8:          <asp:ListBox  runat="server" 9:             Size=1 10:             AutoPostBack=true> 11:             <asp:ListItem>en-US</asp:ListItem> 12:             <asp:ListItem>fr-FR</asp:ListItem> 13:             <asp:ListItem>de-ge</asp:ListItem> 14:             <asp:ListItem>jp-ja</asp:ListItem> 15:          </asp:ListBox> 16:       </form> 17:       <asp:Label  runat="server"/> 18:    </body></html>

The code-behind, exercise1.vb, uses the conversions in the resource files to convert monetary values. It needs to retrieve the currency symbols, so it converts from culture to region by using a case statement; the user selects a culture, which is transferred to a region, which is used to retrieve the currency symbol. The code is as follows:

 1:    Imports System 2:    Imports System.Web 3:    Imports System.Web.UI 4:    Imports System.Web.UI.WebControls 5:    Imports System.Globalization 6:    Imports System.Resources 7:    Imports System.Threading 8: 9:    Public Class ExchangeCalculator : Inherits Page 10:       public lblAnswer as Label 11:       public lblCurrency as Label 12:       public tbValue as TextBox 13:       public lbRegion as ListBox 14: 15:       sub Page_Load(Sender as Object, e as EventArgs) 16:          dim objRM as ResourceManager 17:          dim strLanguage as string = Request.UserLanguages(0). ToString 18: 19:          dim objCulture as new CultureInfo(strLanguage) 20:          Thread.CurrentThread.CurrentCulture = new CultureInfo(strLanguage) 21:          Thread.CurrentThread.CurrentUICulture = new CultureInfo(strLanguage) 22: 23:          dim objRegion as new RegionInfo(GetRegionFromCulture (objCulture.Name)) 24:          lblCurrency.Text = objRegion.CurrencySymbol.ToString 25: 26:          if Page.IsPostBack then 27:             objRM = ResourceManager. CreateFileBasedResourceManager("exchange", _ 28:                Server.MapPath("."), Nothing) 29:             objRegion = new RegionInfo(GetRegionFromCulture (lbRegion.SelectedItem. Text)) 30:             dim dblAnswer as double 31:             dblAnswer = Ctype(tbValue.Text, Double) * CType(objRM.GetString("To" &  lbRegion.SelectedItem.Text), Double) 32:             lblAnswer.Text = objRegion.CurrencySymbol. ToString & dblAnswer.ToString 33: 34:             objRM.ReleaseAllResources 35:          end if 36:       end sub 37: 38:       private function GetRegionFromCulture (strCulture as string) as string 39:          select case strCulture 40:             case "en-US" 41:                Return "us" 42:             case "ja-ja" 43:                Return "jp" 44:             case "de-ge" 45:                Return "de" 46:             case "fr-FR" 47:                Return "fr" 48:          end select 49:       end function 50:    End Class


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