Question

I have a contentview in uiscrollview, I hope to ge hight resolution when uiscrollview zoom in or zoom out in a particular level. I got this aim but screen flash （flash with a view’s background or some tile picture before ）before draw hight resolution content. it’s just not a smooth transition. I refer tiling demo in scrollviewsuite (a apple demo). The difference I did is that I do refresh content in a thread, in this thread I draw content in tile uiview (Actually i want paint a CALayer on background thread). I call it like this:

[self perform: @selector(refreshContent) OnThread:mythread withObject:nil waitUntilDone:YES]

I’ve used waiUntilDone:YES in UI mainthread. wait mythread to repaint content completely. But
I got this situation: the screen flashes some tile content (which not updated) and then gets high resolution content.

If I remove [self perform: @selector(refreshContent) OnThread:mythread... call “refreshContent” directly, the screen doesn’t flash ,update content show on screen immediately,

Someone who be interested and want to help me, you can modify _Tiling demo in apple’s scrollviewsuite demo.. Use a thread to refesh content at another resolution.

all i said is that when update a calayer or uiview ‘s content in a background thread but content not show on screen immediately as i wished… anybody who can help me slove this problem ?

Answer 1

I’ve found a solution for this question. The answser is that you cannot update ui in a thread directly (because when a runloop end in thread, [CATranscation flush] may not be called , so the progress of update screen is not continuos and screen flashed),
but if you want , we can make it like this:

1. Prepare calayer’s contents as a image in the thread as you wanted (image can be rendered from engine such as webkit or download from network).

2. Assign the image which rendered in a thread to calayer’s contents property in mainthread.
   “in main thread”, this is important.

If you do it follow the suggestions above, screen’s flash problem will be removed..

May be someone doubt why render a image in a thread, because I suppose that thread is a
render thread, cann’t render anyting in other thread as well as main thread.