What are Cookies in ASP.NET?
Cookies are small pieces of information stored on the client computer.Use cookies to store small amounts of information on the client’s machine. Web sites often use cookies to store user preferences or other information that is client-specific. Because cookies can be refused, it is important to check whether the browser allows them before you try to create them.They are limited to storing only character data and they are limited to 4K in size.
What are different types of Cookies?
Session Cookies
Persistent Cookies
What are Session Cookies?
Session cookies are stored in-memory during the client browser session. When the browser is closed the session cookies are lost.
How can you create Session Cookies?
You can create session cookies by calling the Add method of the Cookies collection on the Response object. The Cookies collection contains individual cookie objects of type HttpCookie.
//Code to create a UserName cookie containing the name David.
HttpCookie CookieObject = new HttpCookie("UserName", "David");
Response.Cookies.Add(CookieObject);
//Code to read the Cookie created above
Request.Cookies["UserName"].Value;
What is the difference between Session Cookies and Persistent Cookies?
Persistent Cookies are same as Session Cookies except that, persistent cookies have an expiration date. The expiration date indicates to the browser that it should write the cookie to the client's hard drive. Keep in mind that because a user can delete cookies from their machine that there is no guarantee that a cookie you "drop" on a user machine will be there the next time they visit your site.
What are Persistent Cookies used for?
Persistent cookies are generally used to store information that identifies a returning user to a Web site. Typical information found in Persistent Cookies includes user names or user IDs.
How do you create a Persistent Cookie?
You create a persistent cookie the same way as session cookies except that you set the Expires property to a Date in the future which will store the Cookie to the client computer harddrive.
//Code to create a UserName Persistent Cookie that lives for 10 days
HttpCookie CookieObject = new HttpCookie("UserName", "David");
CookieObject.Expires = DateTime.Now.AddDays(10);
Response.Cookies.Add(CookieObject);
//Code to read the Cookie created above
Request.Cookies["UserName"].Value;
What is Cookie Dictionary?
A cookie dictionary is a single cookie object that stores multiple pieces of information. You use the Values property to access and assign new values to the cookie dictionary.
Give an example using Cookie Dictionary?
//Code to create a Cookie Dictionary
HttpCookie CookieObject = new HttpCookie("UserPreference");
//Use the Values property to assign new values to the cookie dictionary
CookieObject.Values.Add("UserName", "David");
CookieObject.Values.Add("Country", "USA");
CookieObject.Values.Add("PreviousVisit", DateTime.Now.ToString());
CookieObject.Expires = DateTime.MaxValue;
//Add the Cookie to the client machine using the Response object
Response.Cookies.Add(CookieObject);
//Code to read the Cookie created above
HttpCookie ObjectCookie = Request.Cookies["UserPreference"];
string UserName = ObjectCookie.Values["UserName"];
string Country = ObjectCookie.Values["Country"];
string PreviousVisit = ObjectCookie.Values["PreviousVisit"];
What are the advantages of Using Cookies?
1. Cookies do not require any server resources since they are stored on the client.
2. Cookies are easy to implement.
3. You can configure cookies to expire when the browser session ends (session cookies) or they can exist for a specified length of time on the client computer (persistent cookies).
What are the disadvantages of Using Cookies?
1. Users can delete a cookies.
2. Users browser can refuse cookies,so your code has to anticipate that possibility.
3. Cookies exist as plain text on the client machine and they may pose a possible security risk as anyone can open and tamper with cookies.
How do you create a Cookie that never expires?
To create a Cookie that never expires set the Expires property of the Cookie object to DateTime.MaxValue.
Are Cookies secure?
No, Cookies are not secure. You must pay attention to the type of data you store in cookies.
1. Cookies are not designed to store critical information so storing passwords in a cookie is a bad idea.
2. Keep the lifetime of a cookie as short as practically possible.
3. Encrypt cookie data to help protect the values stored in the cookie.
01 July, 2009
Interview Questions on ASP.NET controls
What are the 2 types of controls that you can use on a webform in ASP.NET?
Web Server Controls
HTML Controls
What’s the difference between Server controls and HTML controls?
1. Server controls can trigger control-specific events on the server.HTML controls can trigger only page- level events on server (postback).
2. Data entered in a server control is maintained across requests. Server controls retain state.Data is not maintained in an HTML control. Data must be saved and restored using page-level scripts.
3. The Microsoft .NET Framework provides a set of properties for each server control. Properties allow you to change the server control’s appearance and behavior within server-side code.HTML controls have HTML attributes only.
4. Server controls automatically detect browser and adapt display as appropriate.HTML controls do not adapt automatically. You must detect browser in code or write for least common denominator.
What are the 2 Layouts supported by a Web form in ASP.NET?
Grid layout - Controls are placed exactly where you draw them, and they have absolute positions on the page. Use grid layout for Microsoft Windows–style applications, in which controls are not mixed with large amounts of text. Pages using grid layout will not always display correctly in non-Microsoft browsers.
Flow layout - This layout positions controls relative to other elements on the page. If you add elements at run time, the controls that appear after the new element move down. Use flow layout for document-style applications, in which text and controls are intermingled.
When do you choose between GridLayout and Flow layout for Web forms?
You use GridLayout for Web forms that have a fixed appearance. You use FlowLayout for Web forms that incorporate text and controls.When you create controls with GridLayout, Visual Studio adds style attributes to each control that set the position of the control.When you create controls with FlowLayout, Visual Studio omits the style attribute.
Give 3 reasons why we use HTML controls over Server Controls?
Migration from earlier versions of Active Server Pages (ASP) : You can load an ASP application into Visual Studio and revise it gradually, rather than rewrite it completely. Earlier versions of ASP supported only HTML elements, and these elements become HTML controls when you load the project in Visual Studio .NET.
Not all controls require server-side events or state management : This is particularly true when you’re doing data binding. Bound items are usually refreshed from the data source with each request, so it’s more efficient not to maintain state information for bound controls. This means that you can use HTML controls or turn off state management for bound server controls.
You have complete control over what is rendered with HTML controls : ASP.NET adjusts the appearance of server controls based on the browser making the request. HTML controls are not adjusted, so you have direct control over their appearance.
How can you prevent users from editing Text in TextBox control on a web form?
By making the TextBox a readonly TextBox. To make a TextBox readonly set the ReadOnly property to True.
How do you convert an ASP.NET TextBox to accept passwords?
To convert and ASP.NET TextBox to accept passwords set the TextMode property to "Password"
What happens when you set the AutoPostBack property of a TextBox to true?
When AutoPostBack property is set to True, the TextBox control fires a TextChanged postback event when the user leaves the TextBox control after changing the contents. By default, this property is set to False and the TextChanged event is cached until some other postback event occurs.
What are the 3 values that a TextMode property of TextBox can have?
SingleLine : Single Line TextBox
MultiLine : Multi Line TextBox(scrollable)
Password : When set to Password, the text box displays dots in place of the characters typed.
How do you limit the number of characters entered by a user in the ASP.NET TextBox?
By setting the MaxLength property of the TextBox. If you set the MaxLength property to 10, a user can enter only 10 characters into the TextBox.
Web Server Controls
HTML Controls
What’s the difference between Server controls and HTML controls?
1. Server controls can trigger control-specific events on the server.HTML controls can trigger only page- level events on server (postback).
2. Data entered in a server control is maintained across requests. Server controls retain state.Data is not maintained in an HTML control. Data must be saved and restored using page-level scripts.
3. The Microsoft .NET Framework provides a set of properties for each server control. Properties allow you to change the server control’s appearance and behavior within server-side code.HTML controls have HTML attributes only.
4. Server controls automatically detect browser and adapt display as appropriate.HTML controls do not adapt automatically. You must detect browser in code or write for least common denominator.
What are the 2 Layouts supported by a Web form in ASP.NET?
Grid layout - Controls are placed exactly where you draw them, and they have absolute positions on the page. Use grid layout for Microsoft Windows–style applications, in which controls are not mixed with large amounts of text. Pages using grid layout will not always display correctly in non-Microsoft browsers.
Flow layout - This layout positions controls relative to other elements on the page. If you add elements at run time, the controls that appear after the new element move down. Use flow layout for document-style applications, in which text and controls are intermingled.
When do you choose between GridLayout and Flow layout for Web forms?
You use GridLayout for Web forms that have a fixed appearance. You use FlowLayout for Web forms that incorporate text and controls.When you create controls with GridLayout, Visual Studio adds style attributes to each control that set the position of the control.When you create controls with FlowLayout, Visual Studio omits the style attribute.
Give 3 reasons why we use HTML controls over Server Controls?
Migration from earlier versions of Active Server Pages (ASP) : You can load an ASP application into Visual Studio and revise it gradually, rather than rewrite it completely. Earlier versions of ASP supported only HTML elements, and these elements become HTML controls when you load the project in Visual Studio .NET.
Not all controls require server-side events or state management : This is particularly true when you’re doing data binding. Bound items are usually refreshed from the data source with each request, so it’s more efficient not to maintain state information for bound controls. This means that you can use HTML controls or turn off state management for bound server controls.
You have complete control over what is rendered with HTML controls : ASP.NET adjusts the appearance of server controls based on the browser making the request. HTML controls are not adjusted, so you have direct control over their appearance.
How can you prevent users from editing Text in TextBox control on a web form?
By making the TextBox a readonly TextBox. To make a TextBox readonly set the ReadOnly property to True.
How do you convert an ASP.NET TextBox to accept passwords?
To convert and ASP.NET TextBox to accept passwords set the TextMode property to "Password"
What happens when you set the AutoPostBack property of a TextBox to true?
When AutoPostBack property is set to True, the TextBox control fires a TextChanged postback event when the user leaves the TextBox control after changing the contents. By default, this property is set to False and the TextChanged event is cached until some other postback event occurs.
What are the 3 values that a TextMode property of TextBox can have?
SingleLine : Single Line TextBox
MultiLine : Multi Line TextBox(scrollable)
Password : When set to Password, the text box displays dots in place of the characters typed.
How do you limit the number of characters entered by a user in the ASP.NET TextBox?
By setting the MaxLength property of the TextBox. If you set the MaxLength property to 10, a user can enter only 10 characters into the TextBox.
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