NSOutlineView unexpectedly found nil - swift

Question

I am trying to make a file browser in my app that opens in a side panel (with a split view controller).
The source is a URL brought by a prepareForSegue method in the previous viewController.
Each time the vc loads i have the fatal error :
Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value
The compiler locates the error to where i declare :
outlineView.delegate = self
outlineView.dataSource = self
I tried :
1. Undoing and redoing all my outlets connections, by code, by
storyboard
2. Reconnecting delegates and datasource by code, by storyboard
3. I thought maybe something was wrong in my datasource method and i rewrote it 5 times
4. I tried to put my setDelegatesAndDatasource method in the viewDidAppear too, thinking it was a problem of view life cycle
I can't understand what's going on.
Thanks for your help.
'''
extension ViewControllerSource : NSOutlineViewDataSource, NSOutlineViewDelegate {
func setDelegatesAndDatasources(){
outlineView.delegate = self
outlineView.dataSource = self
}
// MARK: - NSOutlineView Datasource
func outlineView(_ outlineView: NSOutlineView, numberOfChildrenOfItem item: Any?) -> Int {
if let fileSystemItem = item as? FileSystemItem {
return fileSystemItem.children.count
}
return 1
}
func outlineView(_ outlineView: NSOutlineView, child index: Int, ofItem item: Any?) -> Any {
if let fileSystemItem = item as? FileSystemItem {
return fileSystemItem.children[index]
}
return rootfileSystemItem
}
func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool {
if let fileSystemItem = item as? FileSystemItem {
return fileSystemItem.hasChildren()
}
return false
}
// MARK: - NSOutlineView Delegate
func outlineView(_ outlineView: NSOutlineView, viewFor tableColumn: NSTableColumn?, item: Any) -> NSView? {
guard let colIdentifier = tableColumn?.identifier else { return nil }
if colIdentifier == NSUserInterfaceItemIdentifier(rawValue: "col1") {
let cellIdentifier = NSUserInterfaceItemIdentifier(rawValue: "cell1")
guard let cell = outlineView.makeView(withIdentifier: cellIdentifier, owner: nil) as? NSTableCellView else { return nil }
if let collection = item as? FileSystemItem {
cell.textField?.stringValue = collection.name ?? "Title not available"
cell.textField?.isEditable = false
cell.textField?.wantsLayer = true
cell.imageView?.image = collection.icon
// cell.textField?.delegate = self
} else {
cell.textField?.stringValue = "unknown item"
cell.textField?.isEditable = false
cell.textField?.wantsLayer = true
}
return cell
} else {
return nil
}
}
}
'''
And here is the main viewController file :
'''
class ViewControllerSource: NSViewController {
#IBOutlet var outlineView: NSOutlineView!
var echo:Echo? {
didSet {
echo!.checkFolderIntegrity()
rootfileSystemItem = FileSystemItem(url: echo!.url)
let window = self.view.window?.windowController as! WindowControllerEcho
window.directoryPath.url = echo!.url
}
}
let propertyKeys: [URLResourceKey] = [.localizedNameKey, .effectiveIconKey, .isDirectoryKey, .typeIdentifierKey]
var rootfileSystemItem: FileSystemItem! {
didSet {
displayItems()
outlineView.reloadData()
}
}
// MARK: - Initialization
override func viewDidLoad() {
super.viewDidLoad()
setDelegatesAndDatasources()
}
func displayItems(){
for fileSystemItem in rootfileSystemItem.children as [FileSystemItem] {
print("item : \(fileSystemItem)")
for subItem in fileSystemItem.children as [FileSystemItem] {
print("\(fileSystemItem.name) - \(subItem.name)")
}
}
}
}
extension ViewControllerSource : EchoDelegate {
func didLoad(echo: Echo) {
self.echo = echo
}
}
'''

Answer 1

The prepareForSegue code reveals the mistake:
You are setting echo in prepareForSegue. This causes to call the property observer didSet. However at this moment the view is not loaded yet and force unwrapping the type crashes.
The solution is to move the code in didSet into viewDidLoad and viewWillAppear and delete the property observer. Nevertheless I recommend to optional bind window
var echo : Echo!
override func viewDidLoad() {
super.viewDidLoad()
setDelegatesAndDatasources()
echo.checkFolderIntegrity()
rootfileSystemItem = FileSystemItem(url: echo.url)
}
override func viewWillAppear(_ animated : Bool) {
super.viewWillAppear(animated)
if let window = self.view.window?.windowController as? WindowControllerEcho {
window.directoryPath.url = echo.url
}
}
Setting delegate and dataSource once is sufficient. If you are using storyboard or Xib the most convenient way is to connect both in Interface Builder.