ios - Could not open OBJ file when convert MDLAsset to MDLMesh - swift

Question

I'm working with demonstrating loading and texturing a .OBJ file using ModelIO.
This code bellow works fine when I use local file.
guard let url = Bundle.main.url(forResource: "myVase", withExtension: "obj") else {
fatalError("Failed to find model file.")
}
let asset = MDLAsset(url:url)
guard let object = asset.object(at: 0) as? MDLMesh else {
fatalError("Failed to get mesh from asset.")
}
But, when I change my code to use file from my Amazon S3 instead of local file. I got errors: "Could not open OBJ file" & "Failed to get mesh from asset."
Here is my code:
let url = URL.init(string: "https://s3.amazonaws.com/myObject/.../object.obj")
let asset = MDLAsset(url:url!)
guard let object = asset.object(at: 0) as? MDLMesh else {
fatalError("Failed to get mesh from asset.")
}
Note: I made the link public and free to download.

Answer 1

I fixed my issue. My issue is that I converted the file before the downloading is finished. Therefore, the local path is created but data is empty because download process hasn't finished yet.
To solve it, I use async to finish downloading first then converting it.
let destination: DownloadRequest.DownloadFileDestination = { _, _ in
let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
let fileURL = documentsURL.appendingPathComponent("myVase.obj")
return (fileURL, [.removePreviousFile, .createIntermediateDirectories])
}
Alamofire.download(urlString, to: destination).response { response in
if response.error == nil, let filePath = response.destinationURL?.path {
print(imagePath)
let myUrl = "file://" + filePath
let asset = MDLAsset(url:URL(string:myUrl)!)
guard let object = asset.object(at: 0) as? MDLMesh else {
fatalError("Failed to get mesh from asset.")
}
...
}
}