Upgrade your extension from Joomla 3.9 to Joomla 4

Documentation and tips

First of all, here are some publications concerning the extension migration from J3 to J4:

docs.joomla.org/Planning_for_Mini-Migrat...mla_3.10.x_to_4.x/en
docs.joomla.org/Potential_backward_compa...ssues_in_Joomla_4/en
docs.joomla.org/Potential_backward_compa...y_issues_in_Joomla_4
developer.joomla.org/news/764-joomla-3-10-and-joomla-4-0.html

JApplication

isAdmin () deprecated 4.0 Use isClient ('administrator') instead.

Replace by

JError

To replace
JError :: raiseWarning ('',
through
JFactory :: getApplication () -> enqueueMessage (
and add 'WARNING' as the last parameter.
JDispatcher

Deprecated class placeholder. You should use JEventDispatcher instead
The CMS 'Event classes will be replaced with the `joomla / event` package

Currently (example):

Remove
replace
by
JRegistry

JRegistry :: getInstance: if the object is to pass the information from the model to the view, retrieve the information in another way (getItem and getState for example)

JViewLegacy

Replace and by:
JDataBase

To replace :

through

Idem it is necessary to replace the $ db-> getErrorNum () and the $ db-> getErrorMsg () by an exception handling as above.

For example, replace:

$ db-> setQuery ($ query);
$ results = $ db-> loadObjectList ();
if ($ db-> getErrorNum ()) {
JFactory :: getApplication () -> enqueueMessage ($ db-> getErrorMsg (), 'WARNING');
return false;
}

through

$ db-> setQuery ($ query);
try {
$ results = $ db-> loadObjectList ();
} catch (Exception $ e) {
JFactory :: getApplication () -> enqueueMessage (JText :: sprintf ('JLIB_DATABASE_ERROR_FUNCTION_FAILED', $ e-> getCode (), $ e-> getMessage ()), 'ERROR');
return false;
}
JHtml

replace JHtml :: _ ('behavior.formvalidation');

by JHtml :: _ ('behavior.formvalidator');

JHtml :: _ ('behavior.tooltip'); // no longer exists
JForm

Use renderField () instead of getControlGroup
Use renderFieldset () instead of getControlGroups

Example :

Look for: form-> getControlGroup (

and replace with form-> renderField (
To install

Replace $ parent-> get ('manifest') -> version

by $ parent-> getManifest () -> version

Some other tips:

error:

Call to undefined method Joomla\CMS\Filesystem\File::read()

change into or

Class 'JRequest' not found
into
or
into

$limitstart = $this->input->get('limitstart', 0, 'int');

error:

500 behavior::framework not found.
into

or some other example
into

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