1) If you invoke the current continuation processing continues after the current page is submitted.
2) If you invoke its parent continuation the current page is resent to the browser.
3) If you invoke the grandparent continuation the actions following submission of the previous page are replayed.
4) If you invoke the great-grandparent continuation the previous page is resent to the browser.
So to implement the "back" button, you invoke (4).
The idea is that instead of only encoding the continuation id in the form or request url, you also associate a "forward" or "back" action with the submit button. The form submits are _always_ submitted to the same location, where some Java or JavaScript code looks at the continuation id together with "forward" or "back" indication of the submit button. If the indication is "forward" then you simply look up the continuation associated with the continuation id and invoke it. But if the indication is "back" then you invoke the great-grandparent of the continuation. With this approach your example reduces to this (and most importantly you don't have to explicitly code back/forward navigation in your flow script):
function myWizard() {
var wizard = new Wizard("wizard-spec.xml");
wizard.show("first-page.html");
wizard.show("second-page.html");
wizard.show("third-page.html");
cocoon.sendPage("finished.html");
}Sylvain Wallez wrote:
Torsten Curdt wrote:
No problem with the wizard approach I suggested: the form contains a link only to *one* continuation (the one that displayed the current page), and upon post, the wizard ressurects the previous continuation.
This means that the current form can be populated and then the previous one displayed.
ok, so let's the say the back button is linked (via POST) to the exact same continuation that got us to that particular view - how should we actually control to go back to the previous one? we are asking for the same one!
sorry, don't get that...
Let's look again at the (still hypothetical) wizard library:
function myWizard() { var wizard = new Wizard(); // register the current execution location as a backtrack point wizard.markStep(); cocoon.sendPageAndWait("first-page.html"); var value = cocoon.request.getParameter("value"); wizard.markStep(); if (value == "foo") { cocoon.sendPageAndWait("foo-page.html"); wizard.handleBack(); } else { cocoon.sendPageAndWait("bar-page.html"); wizard.handleBack(); } wizard.markStep(); cocoon.sendPageAndWait("third-page.html"); wizard.handleBack(); cocoon.sendPage("finished.html"); }
The wizard object contains a stack of continuations. When wizard.markStep() is called, a continuation corresponding to the current location is added on the top of the stack. Notice how wizard.markStep() is called before every page is displayed: this will allow us to go back just before that display.
In wizard.handleBack(), we examine the request for a particular request parameter that indicates that the "previous" button was clicked. If we find this, we pop _two_ continuations from the stack (the first one would just redisplay the same page) and restore that continuation.
When that popped continuation is restored, flowscript execution goes back to the wizard.markStep() statement where this continuation was pushed on the stack. We then redisplay the previous page.
Is it clearer?
Note: (argh, I will obscure things again) implementation-wise, we can't just have a stack in the wizard object, as it would have the same value for all continuations (remember, once an object is declared, its is shared by all descendant continuations). We need a "ContinuationLocal" variable, analogous to "InheritableThreadLocal" but for continuations, i.e. the value will be different for every continuation. This is not available today, even if I have some ideas on how to do it.
Sylvain
