“Cannot preview in this file - Connection interrupted: send previewInstances message to agent" error in Xcode 12

Question

I've got a UIKit project and I'm slowly trying to move to SwiftUI, I created a SwiftUI file and I tried to preview it but I'm getting this error:

Cannot preview in this file - Connection interrupted: send previewInstances message to agent

This is my SwiftUI File:

import SwiftUI

struct LineChart: View {
    var body: some View {
        Text("Hello, World!")
    }
}

struct LineChart_Previews: PreviewProvider {
    static var previews: some View {
        LineChart()
    }
}

I only saw one similar question on StackOverFlow but that didn't help either, is there anyway that I could fix this? Appreciate the feedback!

Hard to help here since it's not reproducible for anyone but you. Have you clicked Diagnostics and/or checked for any crash logs in the Console app — Joakim Danielson, Oct 05 '20 at 14:55
@JoakimDanielson yes, this is the Diagnostics report: ```MessageSendingError: Connection interrupted: send previewInstances message to agent``` — Abdullah Ajmal, Oct 05 '20 at 14:57
@JoakimDanielson Do you know how I could just run this in the simulator? — Abdullah Ajmal, Oct 05 '20 at 15:02
Not from a UIKit project but that information shouldn't be hard to find I assume — Joakim Danielson, Oct 05 '20 at 15:11
@AbdullahAjmal Have you tried cleaning the project & restarting Xcode? (the usual for non-reproducible Xcode problems ) — George, Oct 05 '20 at 20:13
I found a fix here: https://github.com/firebase/firebase-ios-sdk/issues/6574#issuecomment-701427375 — Abdullah Ajmal, Oct 06 '20 at 06:07
For me, I got a similar error message `MessageSendFailure: Message send failure for send previewInstances message to agent`. It turned out the problem was I had recently made my Preview struct `private`, which apparently you can't do for the previews to work. — wristbands, Oct 17 '21 at 01:15

score 9 · Answer 1 · answered Dec 28 '21 at 14:38

9

Turning off "Automatically Refresh Canvas" worked for me. (Xcode 13.2.1)

answered Dec 28 '21 at 14:38

Şafak Gezer

3,928
3
47
49

score 2 · Answer 2 · answered Dec 01 '21 at 11:42

2

Same error, seems that the automatically refresh canvas freeze the preview. Unchecking fixed the problem, but the whole sense of SwiftUI collapses without the automatic update.

answered Dec 01 '21 at 11:42

Alessandro Dovere

31
4

score 1 · Answer 3 · answered Feb 22 '23 at 18:02

1

Same error. Changing simulator worked for me in Xcode 14.2!

answered Feb 22 '23 at 18:02

alamin39

151
1
8

“Cannot preview in this file - Connection interrupted: send previewInstances message to agent" error in Xcode 12

3 Answers3

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