Ajax for client-server communication
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This documentation describes the use of Ajax communication for standard interactions
between a browser and the Ebase Xi server, such as button clicks, hyperlink
clicks, immediate validation requests etc. It does not include Ajax requests initiated from client-side Javascript added by the form developer. Ajax communication can be enabled or disabled
by the developer, but cannot be configured in any other way.
How configured
Ajax
communication between browser clients and the server can be configured via the Form Properties Dialog. The default
setting for new forms is configured using the Designer Preferences Dialog.
How it works
When Ajax communication is
enabled, Ajax
is used wherever possible when posting data from the browser to the server and
to return Html output to the browser. Only the minimum data representing any changed
controls is sent back to the client on each occasion – this is referred to as
an Incremental
Page Refresh for the remainder of this document. This technique
provides significant benefits when the same web page is redisplayed to the
user: the transition is much smoother and the response time is faster. Smoother
transitions provide an enhanced user interface which is more like a native
application.
When Ajax
communication is disabled, a traditional HTTP POST request is sent with each
user request and the entire page is refreshed on each occasion – this is
referred to as a Full Page Refresh for the remainder of this document.
There are many occasions where a Full Page Refresh is required e.g. the application logic routes
control to another page or another form. When these situations are detected,
the initial Ajax
request is processed by the server, then the browser is requested to issue a Full Page Refresh request.
Back Button Considerations
The browser’s history cache (which the browser users for back
button and forward button requests) is not updated when an Incremental Page Refresh is used. Therefore when Ajax is used successfully without the need
for a Full Page Refresh, the user
will not have the ability to return to the page before the request was made.
Instead, the back button will return the user to the page resulting from the
last Full Page Refresh. This
situation will usually apply when the same page is redisplayed.
Use of JSPs with Ajax
When JSP are HTML files are configured on a page, either as
one of the four surrounding JSPS or in an Include Control, these are refreshed according
to the setting of the static content
flag for each JSP or for the control: when a JSP is marked as static, it is not refreshed when that page is redisplayed e.g. as a result of an
event such as a button click or field immediate validation. JSPs
are always refreshed when moving to a different page. The static setting for a JSP can be configured at template level in the
Form Default Properties or at
form level in the Form Properties, or
using the properties an Include Control.