iOS Swift应用程序方向更改非常慢； iOS设备更改方向时会发生什么？

Question

I have a UIViewController that contains a UIScrollView, into which I build all my content for display. I do this because the content is dynamic and depends on data stored in the database.

When I change orientation on an iPhone or in the simulator it takes a long time to perform the change (depending on the data for the display it can be up to 40 seconds).

If I just launch the same controller it takes only a few seconds (it has an overlay and progress indicator so the user knows it's thinking).

Why should the orientation take so long? What actually happens when an orientation change occurs?

Answer 1

How do you load the data from your database, synchronously or asynchronously? You should load it asynchronously if you want a better responsiveness from your app.

Also, if the database is accessed synchronously from the main thread, then where is located that code that loads the data: somewhere in 'viewDidLoad', 'viewDidLayoutSubviews', etc.? I suspect that that loading code runs multiple times when the orientation of the device changes, so you can try to put a breakpoint there and see what exactly happens...