ASP.NET Interview Questions on fragment caching

What is fragment caching?
Caching parts of web form is called as fragment caching. Sometimes you want to cache only part of a Web form response. For instance, a Web form might contain many pieces of variable information plus a single large table that almost never changes. In this case, you might place that table in a Web user control and store the response for that control in cache. This technique is called fragment caching.

What are the steps to follow to cache parts of web form?
To cache part of a Web form, follow these steps:
1. Place the controls and content that you want to cache in a Web user control.
2. Set the caching attributes for that Web user control.
3. Create an instance of the Web user control on the Web form.

What is PartialCaching attribute used for?
You can include the PartialCaching attribute in the control’s class declaration to enable fragment caching.

What are the OutputCache directive attributes that apply only to user controls?
Shared
Cache a single response from a user control for use on multiple Web forms. By default, ASP.NET caches a separate response for each Web form that uses a cached user control. This attribute is only available in the .NET Framework version 1.1 or later.

VaryByControl
Cache multiple responses for a single user control based on the value of one or more controls contained in the user control. Can you cache multiple versions of a user control?Yes, You can cache multiple versions of a user control based on the value of controls contained in a user control (VaryByControl) or based on a custom string (VaryByCustom).

If a user control is read from the cache, can you access its members from code?
No, In general, cached controls are used to present data such as queries from a database, rather than as interactive components. However, if you do need to access a cached control from code, you must first check that the control exists. If the control is read from the cache, you can’t access its members from code. Control members are available only when the control is not read from the cache, such as when the control is first instantiated and when it is reloaded after its cache duration has expired.

When caching is set at both the Web form and user control levels, How does the cache settings interact?
The cache location is determined by the Web form setting. Location settings on a user control have no affect.
If the Web form’s cache duration is longer than the user control’s, both the Web form response and the user control response will expire using the Web form setting.