Thanks Johan, Can I create a wiki page with your answer?
On 7/21/05, Johan Compagner <[EMAIL PROTECTED]> wrote:
>
> >> Is there some documentation somewhere describing how Wicket solves the
> >> Back button problem? My co-worker using JSF has been running into
> >> lots of back-button problems, which makes me realize that I really
> >> don't understand how best to use Wicket to avoid some or all of them
> >> myself.
> >>
> >
> > No docs yet, sorry. Maybe one of my collegues would like to do a short
> > explaination? Gili is the one that came up with the idea btw.
>
> Wicket back button support is based on the same principles of the
> Undo/Redo support in swing.
>
> If you have page versioning enabled (thats default) then everything you
> do on the component level is recorded
> So setting the visibility flag is recorded as a Undoable Change for a
> specific version of that page, The same is for
> replacing components in a page we record the Remove of the old
> component and the Add of a new component.
> When you do something like this then the version number of the page is
> bumped up one. As you can see that in the links
> that are generated to that page.
>
> Then when a action comes in to that page with a smaller version number.
> Then everything that was in recorded
> from the largest version to the version you want are Undo ed.
> So for exampe a visibility Recorded on a component is stored in this class:
>
> protected class VisibilityChange extends Change
> {
> private final Component component;
>
> private final boolean isVisible;
>
> VisibilityChange(final Component component)
> {
> this.component = component;
> this.isVisible = component.isVisible();
> }
>
> /**
> * @see wicket.version.undo.Change#undo()
> */
> public void undo()
> {
> component.setVisible(!isVisible);
> }
> }
>
>
> And that undo is called when an older version is encountered. and the
> undo method will invert the visibility...
>
> Looking now at that code i think holding the visibility flag isn't needed..
> this should also work i believe:
>
> component.setVisible(!component.isVisible());
>
> But i am not sure.. Is it always the invert what a component is now. Or
> what it was then...
>
> You as a developer must record the change if you want model changes to
> be recorded.. That is something
> we can't really do as a framework. (because models can be anything,
> implemented by everybody)
> See Component.modelChanging (should be called before the model is changed)
> and the Component.modelChanged (should be called after the model is changed)
>
> For back button support the first (modelChanging) is the importand one.
>
> But i hope this makes it a bit clearer how the Back button based on
> Undoable changes is working..
>
> johan
>
>
>
>
>
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--
Jon Carlson
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