Making a custom Document type for your app swift UI code example

Example: building an ios file browser

// Create a new document.
func documentBrowser(_ controller: UIDocumentBrowserViewController,
                     didRequestDocumentCreationWithHandler importHandler: @escaping (URL?, UIDocumentBrowserViewController.ImportMode) -> Void) {
    
    os_log("==> Creating A New Document.", log: .default, type: .debug)
    
    let doc = TextDocument()
    let url = doc.fileURL
    
    // Create a new document in a temporary location.
    doc.save(to: url, for: .forCreating) { (saveSuccess) in
        
        // Make sure the document saved successfully.
        guard saveSuccess else {
            os_log("*** Unable to create a new document. ***", log: .default, type: .error)
            
            // Cancel document creation.
            importHandler(nil, .none)
            return
        }
        
        // Close the document.
        doc.close(completionHandler: { (closeSuccess) in
            
            // Make sure the document closed successfully.
            guard closeSuccess else {
                os_log("*** Unable to create a new document. ***", log: .default, type: .error)
                
                // Cancel document creation.
                importHandler(nil, .none)
                return
            }
            
            // Pass the document's temporary URL to the import handler.
            importHandler(url, .move)
        })
    }
}