IOS Error : Main Thread Checker: UI API called on a background thread

Unity Engine
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1

We are currently working on an IOS 11 device with unity 2017.1.0f3 and Xcode 9.5 beta (because Xcode 9 is the only version that currently pushes to IOS 11)

The moment the app starts, we hit this error and our app cannot start -
Main Thread Checker: UI API called on a background thread: -[UIApplication delegate]

This app ran fine before on any previous IOS version (pre IOS 11) when pushed out from Xcode 8
I am hoping that someone else may have ran into this issue and had a workaround as the error itself seems to stem from the core Unity UI in the build - the error throws on our intro scene which has nothing but a Unity UI canvas in it and an image with an animator!

1 Like
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Hello, try using Unity 2017.1.0p3
This seemed to fix a crash I was having too. Wasn’t the same error, but it was related to the UIApplication delegate. Let me know what that does for you.

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3

Ran into this using Unity 2017.1.0p3. Were you able to resolve it?

4

I found that the version of Xcode I was using would throw this error at some point, also possibly related to the version of the ARkit SDK we were using at the time. I would advise trying the latest version of Xcode if possible.

5

same issue with Unity 2017.3.0f3 + Xcode 9.2 (9C40b)

6

I’m seeing this issue as well. Same versions as kavanavak.

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The defect is marked “Fixed in a future release”

Any information from Unity about when that release will come? This is a total showstopper for iOS.

8

Unity 5.6.4 p4 having this issue, any solution yet beside getting final version of Unity ?

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It seems that, Unity released a patch version today ( 12 Jan ) , they fixed the issue, need to test it!

  • (956318) (57809) - iOS: Fixed trampoline calling UI methods ([UIApplication delegate]) from a background thread.
10

Are updates delayed for free users? i can’t get it to update!

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We are on 2017.3.0f3. No patch is available for that version yet. Hopefully in the next few days.

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I am working with xCode11 and Unity 2018.3.5f1, I am getting the same error. My project uses Vuforia model detection to play multiple animations on buttons getting clicked. Can anyone tell me what I should do to get rid of this?

13

Hi Guys,

I’m working on Xcode11.3 and Unity 2018.4.14f1, but I Have the same issue. Do you have any news about this issue?

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2018.3.0f2
Xcode 11.3.1
Same issue.