"Cannot Preview in this file - Failed to launch [App Name]"

I am trying to play around with swiftUI in Xcode 11 and macOS Catalina. BUT After creating a new Project, there is a boiler plate code with a Text that says hello World. I want to have a live preview of this simple welcome message in the canvas by the side of the code.

When i hit the resume button : It says :

Cannot Preview in this file - Failed to launch [App Name]

I've tried hitting the diagnostic button that generated a report to send it to APPLE saying:

[FailedToLaunchError(url: file:///Users/naive/Library/Developer/Xcode/DerivedData/first_swiftUI-dymizjogcbtouhclgjhhefagmcqo/Build/Intermediates.noindex/Previews/first_swiftUI/Products/Debug-iphoneos/first_swiftUI.app, underlying: Error Domain=NSOSStatusErrorDomain Code=-10661 "(null)" UserInfo={_LSLine=3554, _LSFunction=_LSOpenStuffCallLocal}, failureCategory: UVFoundation.FailureCategory.infrastructureFailure) ]

Here's the code, It is the default code that comes with new project created with Xcode 11 and SwiftUI option checked:

import SwiftUI

struct ContentView : View {
    var body: some View {
        Text("Hello World")
    }
}

#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}
#endif

I expect the canvas to show up and display live preview of my code. The canvas is not showing up !!

There are two warning messages generated :

:0: warning: imported declaration 'UITableViewDiffableDataSourceCellProvider' could not be mapped to 'UITableViewDiffableDataSourceReference.CellProvider'

:0: warning: imported declaration 'UICollectionViewDiffableDataSourceCellProvider' could not be mapped to 'UICollectionViewDiffableDataSourceReference.CellProvider'

other than that, My iPad 11"with iPadOS beta runs the app, The simulator is working as well

I encountered this UVFoundation.FailureCategory.infrastructureFailure when starting an iOS app with SwiftUI and then checking the Mac target in the project properties (i.e., using Catalyst to create a cross-platform app). When I did this the default device changed to "My Mac" and preview stopped working, yielding this error in the diagnostic window.

Preview for the Mac target doesn't seem to be supported—you have to select some iOS target ("Generic iOS Device" works just fine for me). Tested on Mojave beta 5 with Xcode 11 beta 5. From the Xcode 11 beta 5 release notes: "Xcode 11 doesn’t support working with SwiftUI in a Mac Catalyst app. (41416222, 51201699)"

"My Mac" selected, it doesn't work!

Working with "Generic iOS device" selected.

I got it fixed by assigning command line tools to xcode 11, it was set to previous version of xcode 10.

Go to : Preferences > location > commandLine tools [drop down] > select xcode 11

Check Diagnostic reports on path ~/Library/Logs/DiagnosticReports. Open fileName.crash file (fileName is the file which causing crash) and search Application Specific Information Fix your code as per the information

Open Terminal and type the following command

sudo xcode-select -s /Applications/Xcode-beta.app/Contents/Developer

and then run sudo xcodebuild -license. Type agree and hit return key to the license. Also select Xcode 11 for Command Line tools from Preference -> Location -> CommandLine in Xcode. This worked for me.

None of the above worked for me - but I did find a way...

  1. Copy the content of the offending file (eg ContentView.swift).
  2. Delete the offending file from your project.
  3. Create a new 'SwiftUI View' and rename it back to whatever file you deleted.
  4. Paste the content you copied in step 1 back in.
  5. Click resume in the canvas.

Comments
  • I got it fixed by assigning command line tools to xcode 11, it was set to previous version of xcode 10. Preferences > location > commandLine tools [drop down] > select xcode 11
  • Two suggestions? (I didn't have this issue but found your question and answer to be potentially valuable to others who may have the same issue.) #1. Reformat your question with good markdown. The errors/warnings are simple text and are hard to read. #2. Post your solution as an answer instead of a comment. (That's perfectly okay to do!) I'd definitely upvote it.
  • Thank you @dfd I filled up the text boxes shown by stackoverflow with my questions as they appear sequentially in a VStack
  • I edited your question, placing "markdown quotes around 4 passages. One last comment - with regards to the two warnings your received, be very aware that you are using a "beta 1" version of something brand new, and as noted in the link, "For example, if you make a mistake in your SwiftUI code you will often get almost incomprehensible error messages." Hopefully this will improve with future betas. wwdcbysundell.com/2019/interviews/paul-hudson
  • thankYou dfd [markdown quotes] i will remember it.
  • This fixed it for me; thank you! Crazy that it can't preview with a Mac device selected, seeing as macOS 10.15 supports SwiftUI, just the same as iOS 13 does.