快速加载多个视图

Question

I was wondering how someone would load multiple UI elements asynchronously. In my case, I have a UIViewController that has a UISegmentControl . Each segment has different UI aspects to load.
For example seg1 shows one image, seg2 shows and image and some text, etc.

If I load all the UI elements before showing the UIViewController then there is a noticeable lag. So I would want to load seg2...n asynchronously to make the UI feel more responsive.

Would I need to load everything via

DispatchQueue.main.async { 
    // load UI
}

For each seg I want to load in the background? Or can I load these elements on another thread and not take up the main thread? I know you're not supposed to update the UI on background threads... But will using the main thread still block the UI if I use async code?

Answer 1

You can't make UI changes on a background thread. Nearly all UIKit calls must be made on the main thread. Therefore you're likely out of luck.

Instead what you should do is do the time consuming number-crunching (downloading and parsing data for example) on a background thread and then use DispatchQueue.main.async() to install the data into your views on the main thread once the time consuming work is done.

If it's the UI setup that is introducing the lag and it's not possible to speed it up then you may be out of luck.