To Lecture Notes

IT 230 -- 4/22/09

Review Questions

1. What is wrong with this tag if you are placing all of your C# code in the .aspx file?
   

   <%@ Page Language=C# AutoEventWireup=true 
                          CodeBehind=Default.aspx.cs 
                          Inherits=WebApplication1._Default %>
   

   Ans: This is a tag for use only with code-behind files. Use this tag instead:

   <%@ Page Language=C# %>
   

2. How do you gray out a control?
   Ans: Set its Enabled property to true.
    
3. What is an overloaded method?
   Ans: A method that has the same name as another method, but with a different signature, that is different parameter classs that are passed in.
    
4. Identify the overloaded methods in the DateTime and Random UML diagrams.
   Ans: In DateTime, the three constructors have the signatures ( ), (int, int, int), and (int, int, int, int, int, int).
    
5. What is a default event?
   Ans: The default event is the event for which the event handler header is produced in Visual Studio when one double clicks on the control.
    
6. What are the default events for these ASP.Net controls?
    
   
   Button   CheckBox   CheckBoxList   DropDownList   TextBox
   
   Ans: Click, TextChanged, CheckedChanged, SelectedItemChanged, SelectedItemChanged.

 
7. Create a Visual Studio Project that tests the default event for a TextBox control.
    
   Ans: Application   Source Code

Posting Pages to the Server

• ASP.Net controls usually post their data to the same page. See Example 29.
   
• Data in HTML controls on an HTML form are posted to a separate .aspx page.
   
• The action and method attributes in the form tag of the HTML page determine where and how the data gets posted. For example
  

  <form action=destination.aspx method=get>
  

• The get method appends data to the end of a URL when posting data. Here is an example URL with appended data

  http://ectweb2.cs.depaul.edu/ssmith/
  destination.aspx?txtName=Stan&txtAge=45
  

• Example 30 uses method=get to post data to the verify1.aspx page. Here is the form tag for posting data with method=post:
  

  <form action=destination.aspx method=post>
  

• The post method submits data in the HTTP header, so there is no appended data to the URL:
  

  http://ectweb2.cs.depaul.edu/ssmith/destination.aspx
  

  
  
• Example 31 uses method=post to post data to the verify1.aspx page.

File IO

• More UML Class Diagrams:
   
  
  StreamReader  StreamWriter 
  
  
• To write to a server file, it must be located in your Database folder on ectweb2:
  

  e:/ectserver/ssmith/Database/
  

• Never use an http URL when opening a StreamReader or StreamWriter object.
   
  
• Look at Examples 35 and 36.
   
  
• To replace the fully qualified names System.IO.StreamReader and System.IO.StreamWriter with the shorter names StreamReader and StreamWriter, use this include statement:
  

  <%@ Import Namespace=System.IO %>
  

• Look at Examples 37.
   
  
• To append to an existing file on the server, create a StreamWriter object with the signature (string, bool). For example

  StreamWriter sw = new StreamWriter(e:/ectserver/ssmith/text.txt);
  

  
  
• Always close a file when finished reading from or writing to it.
   
  
• Look at Examples 38, 39 and 40.
   
  

ASP.Net Validation Controls

• ASP.Net offers validation controls to validate (check the correctness) of a field in a control before it is posted back to the server.
   
• ASP.Net generates JavaScript code to perform this validation.
   
• Here are four validation controls and their use:
   
  

  RequiredFieldValidator	Checks that the field is not blank.
  CompareValidator	Checks that a field is greater than or less then a given value.
  RangeValidator	Checks that a field is within a given range.
  RegularExpressionValidator	Checks a field using a regular expression.

  
  
• A table of Common Regular Expression Symbols
   
• Some Common Regular Expressions shown by the Visual Studio Regular Expression Editor.
   
• Practice Problems on Regular Expressions: write a regular expression that validates each of the following
   
1. Five digit zip code. Example: 64538
    
2. Five digit zip code with optional 4 digit extension. Example: 64538-7346
    
3. One of the letters F, f, M, or m, for male or female. Example: F
    
4. Social security number. Example: 436-43-4399
    
5. Legal C# variable name. Example: entry5
    
6. Telephone number. Example: (312)728-5487
    
7. Illinois drivers license number.


• Use Example 34 to check your answers to the practice problems.
   
• Example 32 uses validation controls to validate the data that is posted back to the same page.
   
• Example 33 uses validation controls, but posts the data to a different page (verify2.aspx).

Projects 3 and 4

• Look at Project 4.
   
• Finish Project 3.

Arrays in C#

• This section on arrays was not covered in class on 1/21, but will be covered later. Read it now as an overview of arrays.
   
• An array is an ordered set of values, all of the same class:
   
Example array of int: {5, 3, 7, 5, 3, 5, 4}
 
Example array of int: {3.32, 1.69, 7.83}
 
Example array of string: {dog, cat, mouse}
 

• Arrays are useful in computer programs because the array elements can be accessed by index. This index can even be a variable, which allows very powerful array processing algorithms to be written.
   
• This C# code finds the average of an array a of double:
  

  int n = 0;
  double sum = 0.0;
  while(n <= a.Length - 1)
  {
      sum += a[i];
      n++;
  }
  double average = sum / a.Length;
  

  
  
• Declare an unitinialized array of int of size 5:
  

  int[ ] a = new int[5];
  

• Declare an initalized array of int:
  

  int[ ] a = {5, 3, 7, 5, 3, 5, 4};
  

• Declare an unitinialized array of int of size 4:
  

  int[ ] x = new double[4];
  

• Declare an initalized array of int:
  

  int[ ] x = {3.32, 1.69, 7.83};
  

• Declare an unitinialized array of int of size 6:
  

  int[ ] s = new string[6];
  

• Declare an initalized array of int:
  

  int[ ] s = {dog, cat, mouse};
  

• The indices and values of an array:
   
  

  Expression	Index	Value
  a[0]	0	5
  a[1]	1	3
  a[2]	2	7
  a[3]	3	3
  a[4]	4	3
  a[5]	5	5
  a[6]	6	4

  
  
• Obtaining the value of the fourth item in the int array a:
  

  value = a[4];
  

• Changing the value of the third item in the int array a:
  

  a[3] = 17;
  

• Examples 18 through 21 show how to use arrays to simplify C# code.