为什么首选 OnCreate 来执行所有主要的应用程序任务？

Question

Why Is onCreate() Preferred To Do All The Main App Tasks? Why not onResume() or onStart() ? Why only onCreate() ? I tried to do the main tasks like binding findViewById() setting text to text views and a lot more. They all work fine. When why do we always are preferred to do that task in onCreate() ?

Answer 1

OnCreate serves as the first entry point into your activity, so logically it makes sense to do as much of the initialization here as possible. Often times there are cases when things need to get configured with higher priority - crash reporting services, dependency injection etc. where this would get escalated to a custom application class.

according to the docs

protected void onCreate (Bundle savedInstanceState)

Called when the activity is starting. This is where most initialization should go : calling setContentView(int) to inflate the activity's UI, using findViewById(int) to programmatically interact with widgets in the UI...

so, I suppose it is fair to say that most initialization will get done inside of onCreate, which usually means that if you were to place this into a lifecycle method which could get executed repeatedly, that could be considered redundant as you'd be assigning the same values to variables repeatedly, unless that's something you actually want to do.

However, lazy initialization is also a concept to keep in mind, being able to initialize something inside of onCreate doesn't always mean that you should, it is often times better to delay initialization until you actually need the instance.

regarding

I tried to do the main tasks like binding findViewById() setting text to text views and a lot more. They all work fine.

they definitely would, findViewById can always be used and isn't limited to being inside of onCreate, in fact the result of findViewById doesn't even have to be assigned to a variable for you to be able to use it