Microsoft Sharepoint Products and Technologies Resource Kit eBook

Chapter 37: Using Visual Studio .NET to Create Web Parts 1021
Instead you can use the Web Part cache to store data to enhance performance.
The Web Part cache can be used in different modes: None, Database, and
CacheObject. The None mode disables caching. In the Database mode, all data is
stored in the SharePoint database. In this mode, Shared and Personal cache entries are
limited to 2 MB. If this limit is exceeded, the cache entry will be lost, and no error will
be displayed. Personal storage data will be charged against the user’s quota. The final
Web Part cache mode, the CacheObjectMode, uses the ASP.NET cache object to store
data. This is also the default mode of the Web Part cache object. Only administrators—
not developers—can set the cache type using the element in the
section of the Web.config file, like this:
..
You can use the CacheType property of the WebPart class to determine the
type of caching used by the Web server. This property is read-only, so it cannot be
used to change the type of caching. Developers can retrieve the cache type at run
time using the following code:
if ( CacheType == CacheType.None )
{
output.Write("Caching is disabled.");
}
else
{
output.Write("Caching is enabled.");
}
The PartCacheWrite method of the WebPart class stores a value in the Web Part
cache. You need to provide this method with a storage type (None, Personal, or
Shared). You also need to provide a key-value pair and determine how long you
want to keep a value stored in the Web Part cache. The following code example
shows how to write data to the Web Part cache:
PartCacheWrite(Storage.Shared, "mykey", "myvalue", TimeSpan.FromMinutes(5));
The PartCacheRead method of the WebPart class can be used to retrieve values
from the Web Part cache again. This is shown in the following code example:
String strValue = PartCacheRead(Storage.Shared, "mykey").ToString();
The PartCacheInvalidate method of the WebPart class can be used to outdate data in
the Web Part cache. You can either outdate all contents of the Web Part cache, outdate
contents of a specific storage type, or mark only a specified cache value of a
specified storage type as outdated. The following code example shows how to outdate
a specific cache value and storage type:
PartCacheInvalidate(Storage.Shared, "mykey");