Stateful controls to replace stateful pages
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Key: CLK-715
URL: https://issues.apache.org/jira/browse/CLK-715
Project: Click
Issue Type: New Feature
Components: core
Affects Versions: 2.2.0
Reporter: Bob Schellink
Assignee: Bob Schellink
Fix For: 2.3.0-M1
Click has been supporting stateful pages for while but these have serious
maintenance and memory issues. Stateful pages also create an inconsistent Click
experience. To develop stateful pages is conceptually much different from
stateless ones since you use the same Page and Control instances from the
previous request. The Page constructor is not invoked for subsequent requests
but the other life cycle events are. This leads to code littered with guarding
checks to ensure duplicate controls are not added to containers.
The main idea behind stateful pages was to create a simple and transparent way
for developers to save state. In other words the state should be handled
implicitly by the framework. I think we missed the sweet spot on this one by
trying to make things too simple and allowing no control over the state
managing.
Since Click is predominantly a stateless framework the majority of use cases
could would involve saving/restoring simple values such as:
- table sort column name and current page number
- form fields values
- active panel name in a TabbedPanel
Instead of trying to hide the complexity my suggestion is to fully expose state
management to the developer. Click is all about server-side development (not
desktop) and I would like to have full control over what goes and does not go
into the application session. This kind of transparency will give me greater
confidence when using stateful controls. If something doesn't work the debugger
will quickly point out where things are going wrong. It would also be easier to
debug the session content since it will mostly consist of primitives and
strings.
My current thinking is to expose an interface Stateful which Controls can
implement:
public void restoreState(Context context)
public void saveState(Context context)
public void clearState(Context context)
Usage:
public MyPage ...
public void onInit() {
table.restoreState(getContext());
}
public void onRender() {
table.saveState(getContext());
}
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