[5.x]: Setting isValid to false in Structures::EVENT_BEFORE_MOVE_ELEMENT causes Server Error

[rogerdawkins]

[5.x]: Setting isValid to false in Structures::EVENT_BEFORE_MOVE_ELEMENT causes Server Error

[brandonkelly]

Just made a change for Craft 4.11 and 5.3 that makes it possible to provide a custom message, by throwing an exception rather than setting $event->isValid = false.

use yii\base\UserException;

Event::on(
    Structures::class,
    Structures::EVENT_BEFORE_MOVE_ELEMENT,
    function (MoveElementEvent $event) {
        // stop the move happening
        throw new UserException('This move isn’t allowed.');      
    }
);

Note that the exception must be an instance/subclass of yii\base\UserException for the message to be shown when Craft isn’t running in Dev Mode.

Thinking about this some more. When you try to drag an entry to a illegal position, such as level 3 of a structure with a max of 2 levels, the system will block it silently, with no Server Error message. So that's what I'm trying to achieve.

In that case, the drop target isn’t available to begin with. So there’s no actual move operation that was ever attempted, as far as the back end knows.

[brandonkelly]

The “server error” message is a bit misleading. All the JS code knows is that the server didn’t accept the new location, so it shows that message and reloads the elements so they revert to their actual positions. That could be due to an actual error that gets logged, but in your case it’s just the result of you setting $event->isValid = false.

[rogerdawkins]

@brandonkelly OK, that's good to know that I'm not doing anything wrong. Can I replace the 'server error' message with something more meaningful for my editors like 'Move not allowed'. I tried adding a setNotice but it doesn't display until the page reloads again.

[rogerdawkins]

@brandonkelly Thinking about this some more. When you try to drag an entry to a illegal position, such as level 3 of a structure with a max of 2 levels, the system will block it silently, with no Server Error message. So that's what I'm trying to achieve. Effectively setting isValid to false I think should replicate an attempted illegal move. Do you think that could be possible?

[rogerdawkins]

@brandonkelly Nice one! That makes it much more friendly, trying to tell users to ignore a 'server error' was going to be a hard sell.