My guess is that you have an image in the Project Setting->Build Phases->Copy Bundle Resources which loses its reference and appears in Red text color. Remove this image from there and re-add.
This happens often due to relocate the image file after adding into project where image was added as a reference instead of a copy.
You can try opening your storyboard or nib as Source Code and then "Find" the image name in it, see if it exists but already invalid in your project, probably you have deleted or changed its name, and now it doesn't seem valid.
Just select the image in Xcode and in right side, File inspector, under 'Target Membership' make sure your project is selected.
Another thing you can do is delete and re insert your image and make sure 'Copy items if needed' is selected and 'Add to targets' your project is selected.
There might be many reasons of this error. To fix this issue you can just follow below given step:
Go to product menu of the Xcode, select clean.
If still you are getting the error, then remove the images from your project and again add the images to your project.
while adding image into the project, make sure that you have selected the Project name inside the "Add to targets". And also enable the "Copy items if needed".
Please Refer below image for better understanding:
PROBLEM
This happened to me seemingly out of the blue on a tab bar controller with icons for each tab. The storyboard was still showing my image icons and the assets existed with the expected names.
MY FIX
Select the tab bar icons in their respective view controller and reassign the image like you did the first time.
Jpeg assets in asset catalogs are not found on iOS 10 or earlier for apps built with Xcode 9. APIcalls for accessing the image such as UIImage.imageNamed: return nil. (32524123)
Workaround: Use png resources or limit app testing to devices running iOS 11 or later.
Xcode9 beta3 release note:
Jpeg assets in asset catalogs are found on iOS 10 or earlier for apps built with Xcode 9.(32524123)
This happened to me as well. I was doing everything right when adding the image but for some reason it was not working. I had to click on the image again once added, and then on the right toolbar under "Target Membership" I noticed my project was not selected even though I was selecting it when adding the image. I selected it here and everything worked fine.
Once selected, go to the right side bar (of XCODE) which is
utilities and under file inspector, scroll to target membership and
select your project target file.
I got the same error message (in XCode 8), even though the app ran fine (in the simulator and on the device).
I found the problem: In my storyboard, using the document outline pane, I clicked through every single UIImage, and looking at the attributes inspector for each UIImage - in the Image View section - found that one UIImage had a blank file name (instead of the .png file name containing the image). Reselecting the .png file name from the dropdown box fixed the error message.
I have just updated to XCode 9 and it started giving me this issue. I created a new Image Set in the Assets section and added the images I wanted to this, then re-added them to my tab bar images with custom names and it worked fine. Hope this helps!
Based on what @hstdt posted above, it made me think I should check that my image is a filetype that doesn't have any bugs related to it. (https://stackoverflow.com/a/44558948/6804257)
I was using a .gif. I got rid of that image and instead used a .png. Now it works.
I pulled my hair out over this issue for hours and none of the solutions in this thread worked. The problem, in the end, was that the Xcode project files were stored on a Google Drive file stream. As soon as I moved it to the local drive or iCloud it worked fine.
Had the same issue and none of these answers worked for me. Instead I restarted the mac and iPhone I was working with and then everything started to work fine again. 🤷♂️
My case was a bit different. I was using an old IBDesignable element which had some property of setting an image directly from the storyboard. Since that element was old, hidden and unused the images it had were not present in my assets folder.
Now Xcode won't be able to search this image since it is not in the project anymore. But if you search in the finder, inside your project, you'll find the XIB/Storyboard in which it is mentioned. From there you can find it manually by opening that XIB or Storyboard as source code and search. Once found either replace them with a new image or remove the unused element.
Look into storyboard file you'll see a question mark icon on any of the imageView (as shown in screenshot below) or UIButton image.
Just correct it and the warning will be gone.
For those that are getting this error while developing a cocoapod
I was trying to use an image from my pod's bundle, thats inside a .xcassets file, in the storyboard. It would show fine in the storyboard but when i ran the app it would crash saying it cant find the resource.
I changed my podspec to include s.resources as well as s.resource_bundles
Xib sets a wrong name for folder reference images. For example I have the folder like Menu->icon.png. Xib sets the "icon" name for the image. It should be "Menu/icon". So do no set images in xibs if you use a folder reference images.