When run a query with WP_Query method, I got an object. I understand that I can then do the loop to display stuffs. But, my goal is not to display anything, instead, I want to get some post data by doing something like "foreach...". How can I get an array of post data that I can loop through and get data?
You should read the function reference for WP_Query on the WordPress codex. There you have a lot of examples to look at. If you don't want to loop over the resultset using a