Do all asthma attacks have "triggers" like viruses, cold air, smoke, etc?

Reactive airways. Asthma, by definition is reactive airways. So it's reacting to something.But often times, we have difficulty narrowing it down to figure out exactly what it is.
Yes. All asthma attacks are caused by various triggers, including allergens such as dust mites, animal dander, foods or pollen, irritants such as tobacco smoke, acid reflux, viral or bacterial infections, exercise, cold exposure, emotional stress, or medications such as beta blockers or nsaids. All individuals with asthma are not the same, so, not all asthma attacks are brought on by the same trigger.
No... Sometimes, an exacerbation of asthma can occur without any known trigger.