Hi Buc,
Thanks for your reply. I’ve tried to implement your second idea because my goal was to only use Expression methods for my dialogs.
What I’ve wanted :
Have a dropdown with two values :
- Create SSH key
- Use existing key
When I choose Create SSH key, a textarea shows up to insert the nex key.
When I choose Use existing key, a dropdown show up to choose the known keypairs.
What I’ve done :
In my form, I have a true/false dropdown and two dynamics fields both hidden by default. In the Customization editor:

Elsewhere in the form, I have a dropdown with my cloud providers and others fields ( like cloud tenant, etc … ).
I’ve created two instances for each dynamic dialog :
- list_os_keypair
- add_new_keypair
For the list_os_keypair, I’ve created those two Expression methods :
To list keypairs for selected cloud provider :
To set the visibility of the dropdown :
I test if the cloud provider status = value of my static dropdown ( true for Use Existing Keypair / false for Create New Keypair )
For the textarea visibilty, I’ve just use a NOT operator with the same expression :
And it works as I wanted ! 
When Use Existing Keypair is selected :
When Create a new keypair is selected :
Maybe it’s not the best or the more beautiful way to do it but it does the job ! With this solution, you need to test the true/false on an available resource.
I’ll try later to improve this to be smoother and easily reusable !
Thanks !