Displaying & working with Core Data in NSTableView - swift

Question

Background: I've been teaching myself Swift, iOS and macOS for a few weeks and I've been trying to put together a 'Price Calculator' for macOS that grabs from a Database of paper and uses the selected properties to select a piece of paper. The user would be able to select from a list of properties such as: Size, Weight, Finish, Color, and Brand. From there it would calculate a price of the paper using general arithmetic.
At first I thought about using a SQLite or a similar Database style program to populate my Calculator – but the User needs to be able to populate the Paper Database themselves. Thus, I've started working with Core Data.
Problem: I have a tableView that's taking the Core Data and displaying the different paper's available – or at least it should be doing that. For testing, I've created a 'Add Paper' button that generates a random Paper and adds it to the Database. I know this is creating random random Paper because I'm able to display it in the Output. But I don't actually know if it's saving.
The problem I have is that when I try to refresh the table and display the Data to the tableView... it either Crashes due to Nil values or it does not add to the tableView.
I've come to the conclusion that I may be displaying the Data wrong to the table -OR- I'm not properly saving the Data -OR- I'm not fetching the Data correctly.
The resources online for iOS only helps so much as this is for Mac OS Any help in this would be appreciated. My Code can be found below and Thank you in advance: NOTE: I'm using the boilerplate AppDelegate file from the CoreData.
Defined in ViewController:
private var papers = [FlatPaper]()
private var appDelegate = NSApplication.shared.delegate as! AppDelegate
private let context = (NSApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
The Add Random Paper button (for testing):
#IBAction func addPaper(_ sender: NSButton) {
let data = PaperData()
let paper = FlatPaper(entity: FlatPaper.entity(), insertInto: context)
paper.paperSize = data.paperSize
paper.paperWeight = data.paperWeight
paper.paperBrand = data.paperBrand
paper.paperColor = data.paperColor
paper.paperFinish = data.paperFinish
paper.paperPrice = data.paperPrice
appDelegate.saveAction(paper)
papers.append(paper)
print("Add Paper Button Pressed. \(paper)")
refresh()
tableView.reloadData()
}
Extensions NSTableDelegate and NSTableDataSource:
extension ViewController: NSTableViewDataSource, NSTableViewDelegate {
// Mark: - Specifying how many rows
func numberOfRows(in tableView: NSTableView) -> Int {
return papers.count
}
// Mark: - Populating the Columns and Rows with Data
func tableView(_ tableView: NSTableView, objectValueFor tableColumn: NSTableColumn?, row: Int) -> Any? {
let paperSpecs = papers[row]
if tableColumn!.title == "Paper Size" {
return paperSpecs.paperSize
} else if tableColumn!.title == "Paper Weight" {
return paperSpecs.paperWeight
} else if tableColumn!.title == "Paper Brand" {
return paperSpecs.paperBrand
} else if tableColumn!.title == "Paper Color" {
return paperSpecs.paperColor
} else if tableColumn!.title == "Paper Finish" {
return paperSpecs.paperFinish
} else {
return paperSpecs.paperPrice
}
}
// Mark: - Refresh Method for reloading all of the data
private func refresh() {
do {
papers = try context.fetch(FlatPaper.fetchRequest())
} catch let error as NSError {
print("Could not fetch. \(error), USER INFO: \(error.userInfo)")
}
}
}

Answer 1

In tableview:objectValueFor you should get your paper specs object from your array using the row argument instead of creating a new (empty) instance.
let paperSpecs = papers[row]
You might also want to look into NSFetchedResultsController, it’s really helpful when working with Core data and table views.