INTERVIEW QUESTIONS MICROSOFT ASP.NET 2.0 DETAILS

Question: What is Viewstate?

Answer: The web is a stateless medium - state is not maintained between client requests by default. Technologies must be utilized to provide some form of state management if this is what is required of your application, which will be the case for all but the simplest of web applications. ASP.NET provides several mechanisms to manage state in a more powerful and easier to utilize way than classic ASP.

Page level state is information maintained when an element on the web form page causes a subsequent request to the server for the same page - referred to as 'postback'. This is appropriately called ViewState as the data involved is usually, though not necessarily, shown to the user directly within the page output.

The Control.ViewState property is associated with each server control in your web form and provides a dictionary object for retaining values between such multiple requests for the same page. This is the method that the page uses to preserve page and control property values between round trips.

When the page is processed, the current state of the page and controls is hashed into a string and saved in the page as a hidden field. When the page is posted back to the server, the page parses the view state string at page initialization and restores property information in the page.

ViewState is enabled by default so if you view a web form page in your browser you will see a line similar to the following near the form definition in your rendered HTML:

ViewState offers a substantial improvement over the two competing techniques for state management via the client: standard hidden fields and cookies, in that ViewState is not limited to the storage of simple values. You can use ViewState to store any object as long as it is serializable, and the standard VB.NET types are. Serialization is the process of storing an object's data and other information necessary to reconstruct the object later.

There is a further complication: a type that either is serializable or has a TypeConverter defined for it can be persisted in ViewState. However, types that are only serializable are slower and generate a much larger ViewState than those that have a TypeConverter. The TypeConverter class provides a unified way of converting types of values to other types, as well as for accessing standard values and subproperties.

ViewState is serialized using a limited object serialization format that is optimized for primitive types, and for String, ArrayList, and HashTable types. You may want to consider these issues if page performance concerns are key

The web is a stateless medium - state is not maintained between client requests by default. Technologies must be utilized to provide some form of state management if this is what is required of your application, which will be the case for all but the simplest of web applications. ASP.NET provides several mechanisms to manage state in a more powerful and easier to utilize way than classic ASP.

Page level state is information maintained when an element on the web form page causes a subsequent request to the server for the same page - referred to as 'postback'. This is appropriately called ViewState as the data involved is usually, though not necessarily, shown to the user directly within the page output.

The Control.ViewState property is associated with each server control in your web form and provides a dictionary object for retaining values between such multiple requests for the same page. This is the method that the page uses to preserve page and control property values between round trips.

When the page is processed, the current state of the page and controls is hashed into a string and saved in the page as a hidden field. When the page is posted back to the server, the page parses the view state string at page initialization and restores property information in the page.

ViewState is enabled by default so if you view a web form page in your browser you will see a line similar to the following near the form definition in your rendered HTML:

ViewState offers a substantial improvement over the two competing techniques for state management via the client: standard hidden fields and cookies, in that ViewState is not limited to the storage of simple values. You can use ViewState to store any object as long as it is serializable, and the standard VB.NET types are. Serialization is the process of storing an object's data and other information necessary to reconstruct the object later.

There is a further complication: a type that either is serializable or has a TypeConverter defined for it can be persisted in ViewState. However, types that are only serializable are slower and generate a much larger ViewState than those that have a TypeConverter. The TypeConverter class provides a unified way of converting types of values to other types, as well as for accessing standard values and subproperties.

ViewState is serialized using a limited object serialization format that is optimized for primitive types, and for String, ArrayList, and HashTable types. You may want to consider these issues if page performance concerns are key

Source: CoolInterview.com

View state data is maintained as a hidden field and automatically returned to the server with every postback.

You can store the information in viewstate, that will be accessed during only in pageload and the next time its returned to the server Source: CoolInterview.com

Viewstate is use to provide state managemet at page level. Source: CoolInterview.com

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