Introduction - If you have any usage issues, please Google them yourself
In the realization of a page or in the realization of a class method, because the page is complex, class is complex, it is often not a " one-step" to achieve, but gradually progressive, forward-propelled small step, that is, first achieve the required functionality for a small part of the run, debug, modify the error, correct, and then realize another small part of functionality, run, debug, modify the error, and so on, until the final realization of the pages or the class function.