Storing and Accessing Custom Data in Custom Adaptive Tags
To store custom data as member variables using a custom
tag, use the SetStateVariable or SetStateSharedVariable methods. To retrieve it, use GetStateVariable or GetStateSharedVariable.
Standard variables (stored with
SetStateVariable) can only be accessed by tags in the same library. Shared variables
(stored with
SetStateSharedVariable) can be accessed
by tags from any library. To prevent tags from other libraries from
editing a shared variable, set
bOwnerEditOnly to
true when the shared variable is stored (tags in other libraries will
still be able to read the variable).
The
Scope parameter determines who can see the data and how long it stays
in memory. The following options are defined in the
Scope class:
| Application Scope |
Data is visible to all tags and all users, and is only removed
when the application is restarted. Therefore, care should be used
when storing data on the application to make sure it does not become
cluttered with large amounts of data. |
| HTTP Request Scope |
Data will be visible to all tags in the same HTTP Request as
the current tag, and is removed from memory when the HTTP Request
is finished. |
| Session Scope |
Data is visible to all tags for the current user, and is cleared
from memory when a user logs out and logs in again. |
| Persistent Session Scope |
Data is visible to all tags in the same HTTP session, and is
only removed from memory when the browser is closed or the browser
session times out. Note: Data is not cleared on user logout, so do
not cache anything on this scope that could be considered a security
risk if it was leaked to another user. Most tags should use Session
Scope for HTTP Session data storage (as described above). |
| Portlet Request Scope |
Data is visible to all tags in the same portlet as the current
tag, and is removed from memory when the portlet is finished displaying.
Tags in other portlets on the same page will not be able to see the
data. |
| Tag Scope |
Data can only be seen by children of the current tag and is
removed from memory when the tag is finished. (For example, in the
following tags: <pt:atag><pt:btag/></pt:atag><pt:ctag/>,
data stored in Tag Scope by "atag" would be visible to "btag" but
not to "ctag.") |
If data is stored directly in the tag in member variables
(not recommended), override the
ReleaseTag method
to release the data stored on the tag.
/**
* @see com.plumtree.portaluiinfrastructure.tags.ATag#ReleaseTag()
*/
public void ReleaseTag()
{
// Release all member variables.
m_strPreviousRequestURL = null;
}
Note: Displaying an HTMLElement in
a tag and caching it so another tag can add more HTML is not supported. HTMLElement trees can be generated and stored for later
use as long as they are self-contained trees and used in a read-only
way. It is safest to clone a cached HTMLElement tree before trying to display it again to make sure there are no
threading problems.
Note: It is a best practice not to use static
fields for data storage in tags. Each tag instance is guaranteed
to be accessed by only a single thread at a time, but there may be
multiple threads accessing different instances of the same tag class
at the same time, either from the same user or a different user. This
means that any static fields must be accessed using synchronized methods.
Since there can be multiple instances of the same tag running
at the same time, state variables set in shared scopes (Session, Persistent
Session and Application) could change values during the execution
of a single tag.
