We may think we know when the next OnePlus flagship will be officially unveiled. However, the company's chief executive officer (CEO) has stated that the applicable rumors will be confirmed or denied on April 23, 2019. Judging by the typical product cycle associated with this company, the event itself is likely to follow in about a month from then.
https://www.notebookcheck.net/OnePlus-7-launch-date-to-be-announced-next-Tuesday.418271.0.html