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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