After the patent is declared invalid, does the previous production and sales behavior constitute infringement?

Some netizens asked whether the previous production and sales behavior constituted infringement after the design patent was declared invalid. What is the legal basis? After the patent is declared invalid, the previous production and sales behavior constitutes infringement. Lawyers believe that if a patent is declared invalid, then according to the provisions of the patent law, the patent does not exist from the beginning, that is, the patent is considered to have never taken effect. Therefore, we can't claim rights with the effect before invalidity. If the other party's patent right is firm, then the user will bear the tort liability. After the patent is declared invalid, does the previous production and sales behavior constitute infringement? If you don't want to be sued for infringement, you can use the following methods: 1. Check whether there is enough evidence and reason to declare the patent right of the other party invalid. 2. If the other party's patent right is stable, it can request patent license and continue to produce, implement and sell patented products.