Answers for Day 19

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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. graphics/ccc.gifText)) 30:             dim dblAnswer as double 31:             dblAnswer = Ctype(tbValue.Text, Double) * CType(objRM.GetString("To" &  graphics/ccc.giflbRegion.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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    Sams Teach Yourself ASP. NET in 21 Days
    Sams Teach Yourself ASP.NET in 21 Days (2nd Edition)
    ISBN: 0672324458
    EAN: 2147483647
    Year: 2003
    Pages: 307
    Authors: Chris Payne

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