 | Sams Teach Yourself ASP.NET in 21 Days, Second Edition
By Chris Payne
| | Table of Contents | | | Appendix A. Answers to Quiz Questions |
Quiz | 1: | What is the difference between a file and a stream? | | A1: | A file is a physical collection of data residing on a computer. A stream is a way to access data from different locations, such as a file, memory, or over the network. | | 2: | What are the six FileMode values? | | A1: | Append, Open, OpenOrCreate, Create, CreateNew, and Truncate | | 3: | What does the Peek method do, and why is it helpful? | | A1: | The Peek method reads the next character from a stream, but doesn't actually return the character. It is useful for determining when you're at the end of a stream. | | 4: | How do you verify the existence of a file or directory on a server? | | A1: | The FileExists or DirectoryExists methods from the File and Directory classes, respectively. | | 5: | Use the File object to open a file called userdata.txt in the root directory of your c: drive, for appending. If this file doesn't exist, use the File object to create it, and make sure that no other applications can access this file while you are using it. | | A1: | dim f as new File("c:\userdata.txt") f.Open(FileMode.Append, FileAccess.ReadWrite, FileShare.None) |
Exercises | 1: | Create an ASP.NET page that will open a file specified by a user in a text box, and display the contents in a label. Make sure to check whether the file exists. Note that the user must be required to enter the full path to the file as well. | | A1: | The code for the answer is as follows: 1: <%@ Page Language="VB" %> 2: <%@ Import namespace="System.IO" %> 3: 4: <script runat="server"> 5: sub DisplayFile(Sender as Object, e as EventArgs) 6: dim strFile as string = tbFile.Text 7: dim objReader as StreamReader 8: 9: if strFile <> "" then 10: if File.Exists(strFile) then 11: objReader = new StreamReader(strFile) 12: 13: lblMessage.Text = "<pre>" 14: while objReader.Peek > -1 15: lblMessage.Text += Server.HTMLEncode _ 16: (objReader.ReadLine) & "<br>" 17: end while 18: lblMessage.Text += "</pre>" 19: 20: objReader.Close 21: end if 22: end if 23: end sub 24: </script> 25: 26: <html><body> 27: <form runat="server"> 28: <asp:TextBox runat="server" 29: OnTextChanged="DisplayFile" 30: AutoPostBack=true /><p> 31: 32: <asp:Label runat="server" 33: MaintainState=false/> 34: </form> 35: </body></html> | | 2: | Modify Exercise 1 so that the content of the file is displayed in an editable text box. Allow the user to make changes, and when the user clicks a submit button, write the changes back to the file. | | A1: | 1: <%@ Page Language="VB" %> 2: <%@ Import namespace="System.IO" %> 3: 4: <script runat="server"> 5: sub Page_Load(Sender as Object, e as EventArgs) 6: if not Page.IsPostBack then 7: tbContents.Visible = false 8: end if 9: end sub 10: 11: sub DisplayFile(Sender as Object, e as EventArgs) 12: dim strFile as string = tbFile.Text 13: dim objReader as StreamReader 14: 15: if strFile <> "" then 16: if File.Exists(strFile) then 17: if not tbContents.Visible then 18: tbContents.Visible = true 19: else 20: tbContents.Text = "" 21: end if 22: 23: objReader = new StreamReader(strFile) 24: 25: tbContents.Text = Server.HTMLEncode _ 26: (objReader.ReadToEnd) 27: objReader.Close 28: else 29: tbContents.Text = "Invalid file" 30: end if 31: end if 32: end sub 33: 34: sub WriteFile(Sender as Object, e as EventArgs) 35: dim strContents as string = tbContents.Text 36: dim strFile as string = tbFile.Text 37: dim objWriter as StreamWriter 38: 39: if File.Exists(strFIle) then 40: objWriter = new StreamWriter(strFile, false) 41: 42: objWriter.Write(strContents) 43: 44: objWriter.Close 45: end if 46: 47: end sub 48: </script> 49: 50: <html><body> 51: <form runat="server"> 52: <asp:TextBox runat="server" 53: OnTextChanged="DisplayFile" 54: AutoPostBack=true /><p> 55: 56: <asp:TextBox runat="server" 57: visible=true 58: TextMode="Multiline" 59: Columns="50" 60: rows="20" /><p> 61: 62: <asp:Button runat="server" 63: OnClick="WriteFile" 64: Text="Submit"/> 65: </form> 66: </body></html> |
|
|
