Are the #If Debug Statements Really Needed for Previews in Swiftui to Remove It in a Release Build

How do you check if SwiftUI is in preview mode?

You can detect this using ProcessInfo.processInfo.environment["XCODE_RUNNING_FOR_PREVIEWS"]. The value will be "1" at runtime when running in the canvas.

How to get Previews working again in a SwiftUI project

I think I have solved this. I had made what probably sounds like a stupid mistake. The project uses CoreData and I had given one of the Entities the same name as the project.
Whilst that might sound crazy, the project would build and run (simulator or device) without a problem. It was just the preview that was getting confused.
I have renamed the Entity and at least some of the Views can be previewed, including the TestView mentioned above.
There are still a couple of Views not previewing correctly, but I think that is due to another issue.

Xcode 12.3 SwiftUI Preview 1 of Content View Previews not found in any targets

By chance, I recognized why the previews were broken in my from-scratch-project. Reason was the "Versioning" build phase that I originally added during setup:

xcrun agvtool next-version -all

After wrapping that into a Previews check, everything's fine again:

if [ $ENABLE_PREVIEWS == "NO" ]
then
    xcrun agvtool next-version -all
fi

SwiftUI: Automatic preview updating paused, always

The problem with all the given answers is that you need to check or uncheck your script in debug mode if you want to make the preview work.

Here is a convenient alternative using the environment variables.

This is really simple

Embed all the content of your script in an if statement that check if we're using the preview or not. If we're in preview, then don't run the content of your script, otherwise, let's run it. And you don't have to sacrifice your script for release versions only.

Here is the template :

if [ $ENABLE_PREVIEWS == "NO" ]
then
  # your code to execute here
else
  echo "Skipping the script because of preview mode"
fi

And below a full example that I use to bump my build version number

# xcode-build-bump.sh
# @desc Auto-increment the build number every time the project is run.
# @usage
# 1. Select: your Target in Xcode
# 2. Select: Build Phases Tab
# 3. Select: Add Build Phase -> Add Run Script
# 4. Paste code below in to new "Run Script" section
# 5. Drag the "Run Script" below "Link Binaries With Libraries"
# 6. Insure that your starting build number is set to a whole integer and not a float (e.g. 1, not 1.0)
if [ $ENABLE_PREVIEWS == "NO" ]
then
  buildNumber=$(/usr/libexec/PlistBuddy -c "Print CFBundleVersion" "${PROJECT_DIR}/${INFOPLIST_FILE}")
  buildNumber=$(($buildNumber + 1))
  /usr/libexec/PlistBuddy -c "Set :CFBundleVersion $buildNumber" "${PROJECT_DIR}/${INFOPLIST_FILE}"
else
  echo "Skipping Bump of version"
  echo $ENABLE_PREVIEWS
fi

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