SetActionHidden() is used to modify the action's default view so that it can be visible or hidden. The method invocation needs two arguments:
CALL DIALOG.SetActionHidden("action", boolean)
The action argument is a string (lower case is a must) which defines the action influenced by the method. The action can be identified fully or partially. If the last is the case, the missing information is automatically filled depending on the context:
dialog_name is a string containing the name of a singular dialog or a sub-dialog. field_name is a string identifying the field used in an INFIELD clause of an ON ACTION block. If SetActionActive() is used within a sub-dialog, the identifier of this sub-dialog can be omitted.
If the method does not find the action specified in the action argument a run-time error will occur.
In a singular interaction statements like INPUT, the field-specific actions can be referenced by field_name.action_name structure if the dialog definition did not contain the NAME attribute.
Boolean attribute specifies whether the action is hidden. The attribute should be represented as 1 (TRUE, the action is hidden) or 0 (FALSE, the action is visible).
There is some specifics about using variables with ui.Dialog methods.
You can learn about them here.