Nested subqueries built with NSExpression crashes but not its predicate

See also questions close to this topic

• SwiftUI, apply drawGesture only when over Image

  I'm try to apply the gesture only when the user is over the Image display not when tapped outside the image.

  Any suggestion how I can do? this following code draw also when user tap outside the image.

  struct ContentView: View {
      @StateObject var am = AppManager()
      @State var switchToTakePicture = false
      @State var paths: [PathContainer] = []
      @State var currentDraggingId = UUID()
      @State var spikoPic = #imageLiteral(resourceName: "spiko-16.jpeg")
      @State var centerOFimage = CGSize(width: 0, height: 0)
      var body: some View {
          
          GeometryReader { proxy in
              ZStack {
                  Image(uiImage: spikoPic)
                      .resizable()
                      .scaledToFit()
                      .position(x: proxy.size.width/2, y: proxy.size.height/2)
                      .background(GeometryReader {
                          Color.clear.preference(key: ViewRectKey.self,
                                                 value: [$0.frame(in: .global)])
                      })
                      .gesture(drawGesture) // not correct
                  
                  ForEach(paths) { container in
                      // draw and set the foreground color of the paths to red
                      container.path
                          .stroke(Color.red, lineWidth: 4)
                      
                      
                  }
              }
              .onPreferenceChange(ViewRectKey.self) { rects in
                  print(rects.first ?? .zero)
                  
              }
          }
          
      }
      var drawGesture: some Gesture {
          
          DragGesture(minimumDistance: 0)
              .onChanged { value in
                  
                  // The point that the gesture started from
                  let start = value.startLocation
                  // The point that the gesture ended to
                  let end = value.location
                  // the properties of the rectangle to be drawn
                  let rectangle: CGRect = .init(origin: end,
                                                size: .init(width: start.x - end.x,
                                                            height: start.y - end.y))
                  // create a path for the rectangle
                  let path: Path = .init { path in
                      
                      path.addRect(rectangle)
                  }
                  
                  print("rettangolo = \(rectangle) orig \(rectangle.origin) - height \(rectangle.height) width = \(rectangle.width)")
                  
                  // remove the previous rectangle that was drawen in current
                  // process of drawing
                  paths.removeAll { $0.id == currentDraggingId }
                  // append the new rectangle
                  paths.append(.init(id: currentDraggingId, path: path))
              }
              .onEnded { _ in
                  // renew the dragging id so the app know that the next
                  // drag gesture is drawing a completely new rectangle,
                  // and is not continuing the drawing of the last rectangle
                  currentDraggingId = .init()
              }
      }
  }
  
  
  

  i want no box outside

  
• How to navigate between NavigationLink while leave a part of main window stay the same in SwiftUI

  I would like to navigate between different NavigationLinks in NavigationView while some part of the main window stay the same. For example, I want to make a music app and I want to let the play controller always on top, while I can display different navigation contents (songs page, artists page...) using the rest of the window.

  Like what's showed in the picture below, I want to keep the red part always there while the blue part changes.

  Navigation Example Picture

  My code would be like below, but it won't work correctly. The AlwaysStayView() disappears when I click any NavigationLink on sidebar. So, how can I correct it or is there any solution (prefer in SwiftUI, but framework like UIKit would also be OK). I would appreciate it.

  NavigationView {
              List {
                  NavigationLink { DiscoverView() }
                      label: { Label("Discover", systemImage: "magnifyingglass") }
                  NavigationLink { SongsView() }
                      label: { Label("Songs", systemImage: "music.note") }
                  NavigationLink { ArtistsView() }
                      label: { Label("Artists", systemImage: "music.mic") }
                  }
              }
              .listStyle(SidebarListStyle())
  
              VStack {
                  AlwaysStayView()
                  SongsView()
              }
  }
  
• NumberFormatter and unsigned with UInt64.max

  I'm trying to create a string representing UInt64.max using NumberFormatter. Here's the code:

  let formatter = NumberFormatter()
      
  formatter.usesGroupingSeparator = true
  formatter.numberStyle = .decimal
  formatter.positiveFormat = "# ##0.#########"
  formatter.maximumSignificantDigits = 20
  formatter.usesSignificantDigits = false
  formatter.maximumFractionDigits = 20
  formatter.minimumFractionDigits = 0
  formatter.alwaysShowsDecimalSeparator = false
  // formatter.roundingMode = .halfUp
  let text1 = formatter.string(for: NSNumber(value: Int64.max))
  let text2 = formatter.string(for: NSNumber(value: UInt64.max))
  
  print(text1)
  print(text2)
  

  which prints:

  Optional("9,223,372,036,854,780,000")
  Optional("-1")

  but should print

  Optional("9223372036854775807")
  Optional("18,446,744,073,709,551,615")

  It looks like NSNumber is rounding Int64 and isn't taking the UIn64. The obj-c version of NSNumberFormatter works fine.

  Am I missing something or is there a problem with NumberFormatter?
• Dynamically add textfields with a for each loop and a button in swiftUI

  I am trying to use a ForEach loop to dynamically add textfields inside a form section with a button.

  Form {
                  ForEach(0..<numberOfItems, id: \.self) { _ in
                      TextField("", text: $listItemEntry)
                  }
                  Button("Add Item") {
                      numberOfItems = numberOfItems + 1
                  }
              }
  

  How would I replace the $listItemEntry which is currently bound to a state variable so that I can individually type in each text field. As a bonus, what would be the best way to save these entries to CoreData, as I don't really know where to start.
• Core data creates keeps populating with default values and doesn't save on close

  I am fairly new to core data. I am trying to make a form where each time I add a section header and text from a sheet view, it appears within a new section. The problem I am having is every time I open the sheet view to enter the section header and text saved via core data, a big list of my default values of List Name and List Section appears on the main screen upon dismissing the sheet view. They also disappear after a relaunch so I don't think I am saving the data correctly.

  

  I currently have the core data entity of Lists with the attributes of listName and listSection which are used in my form as seen in the image.

  struct ContentView: View {
   @Environment(\.managedObjectContext) var moc
   @FetchRequest(sortDescriptors: []) var lists: FetchedResults<Lists>
  
  var body: some View {
          NavigationView {
              Form() {
                  ForEach(lists) { list in
                      Section(header: Text(list.listSection ?? "List Section")) {
                          NavigationLink {
                              Text("Next Page")
                          } label: {
                              Text(list.listName ?? "List Name")
                          }
                      }
                  }
              }
        }
  }
  

  I create this data via a sheet view. I also use the var dismiss to hide the sheet view, bringing me back to my main view code shown above.

  struct AddList: View { 
      @Environment(\.dismiss) var dismiss
     
      @State private var listNameEntry: String = ""
      @State private var listSectionEntry: String = ""
      
      @Environment(\.managedObjectContext) var moc
      @FetchRequest(sortDescriptors: []) var lists: FetchedResults<Lists>
      
      var body: some View {
          let list = Lists(context: moc) //used to save to core data
  
              Form {
                  Section() {
                      TextField("List Name", text: $listNameEntry) {
                          list.listName = listNameEntry
                      }
                      TextField("List Section", text: $listSectionEntry) {
                          list.listSection = listSectionEntry
                      }
                  }
                  Section() {
                      Button("Done") {
                          try? moc.save()
                          dismiss()
                      }
                  }
              }
   }
  
• Core data - TableView - Toggle - Index out of range

  I have a data model like this. The data is connected to core data.

  import Foundation
  import CoreData
  @objc(Aktie) class Aktie: NSManagedObject {
      @NSManaged var isCompleted: Bool
      @NSManaged var counter: String?
      @NSManaged var deletedDate: Date?
      @NSManaged var id: NSNumber!
      @NSManaged var notes: String?
      @NSManaged var title: String?
      @NSManaged var type: String?
      @NSManaged var point: String?
      @NSManaged var saving: String?
  }
  

  I have made a toggle in my tableview - the relevant code is as follows.

  var akties: [Aktie]=[]
  
  override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) ->UITableViewCell {
      let aktieCell=tableView.dequeueReusableCell(withIdentifier: "aktieCellID", for: indexPath) as! AktieCell 
      let thisAktie: Aktie! 
      thisAktie=nonDeletedNotes()[indexPath.row]    
      aktieCell.aktieTitle.text=thisAktie.title 
      aktieCell.aktieType.text=thisAktie.type 
      aktieCell.AktieCounter.text=thisAktie.counter 
      aktieCell.AktiePoints.text=thisAktie.point 
      aktieCell.accessoryType=thisAktie.isCompleted ? .checkmark: .none
      
      override func tableView(_ tableView: UITableView, leadingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
          let complete=UIContextualAction(style: .normal, title: "Completed") {
              (action, sourceView, completionHandler) in // print("Completed")
              let cell=tableView.cellForRow(at: indexPath) as! AktieCell 
              self.akties[indexPath.row].isCompleted=(self.akties[indexPath.row].isCompleted) ? false: true 
              cell.accessoryType=(self.akties[indexPath.row].isCompleted) ? .checkmark: .none 
              completionHandler(true)
          }
          complete.backgroundColor=.systemGreen 
          complete.image=self.akties[indexPath.row].isCompleted ? UIImage(named: "undo"): UIImage(named: "tick")
          let swipeConfiguration=UISwipeActionsConfiguration(actions: [complete]) 
          return swipeConfiguration
      }
  

  The code builds the app without any error but when I try to swipe the row it stops and gives me the following error:

  Thread 1: Fatal error: Index out of range.
• Can someone please explain the query shown in depth?

  Question: write a SQL query to find the salespeople from the given tables who had more than one customer. Return salesman_id and name.

  Sample table: customer

  customer_id	cust_name	city	grade	salesman_id
  3002	Nick Rimando	New York	100	5001
  3007	Brad Davis	New York	200	5001
  3005	Graham Zusi	California	200	5002
  3008	Julian Green	London	300	5002
  3004	Fabian Johnson	Paris	300	5006
  3009	Geoff Cameron	Berlin	100	5003
  3003	Jozy Altidor	Moscow	200	5007
  3001	Brad Guzan	London		5005

  Sample table: salesman

  salesman_id	name	city	commission
  5001	James Hoog	New York	0.15
  5002	Nail Knite	Paris	0.13
  5005	Pit Alex	London	0.11
  5006	Mc Lyon	Paris	0.14
  5007	Paul Adam	Rome	0.13
  5003	Lauson Hen	San Jose	0.12

  Solution

  SELECT salesman_id,name 
  FROM salesman a 
  WHERE 1 < (SELECT COUNT(*) 
             FROM customer 
             WHERE salesman_id = a.salesman_id);
  

  So basically am unable to understand the subquery how can we compare two table column without using the joins and secondly how this where condition is working as a group by as well and provide the count. So if someone can help me understand this subquery in depth with easy language then it would be really helpful.

  This question and solution is correct because am practicing on W3resource and you can find this question under the topic of SQL Subquery Exercises in the exercise 11.
• Subquery with an Exist

  I am a user working in inventory management attempting to return information regarding product name, location, and its availability at the location from the adventure works 2017 database. While trying to run the query, I am getting an error message that states I have too many expressions in my subquery list and that I can only do that if I start the subquery with 'Exists'. I suppose I do not understand what I am doing wrong, maybe someone could explain how 'Exists' works? Is there a way I can rewrite this so I can return both expressions in the subquery? I will include the syntax and error message below.

  SELECT Production.Product.Name
         ,(SELECT Production.Location.Name
           ,Production.Location.Availability
           FROM Production.Location
           WHERE Production.Location.LocationID = Production.ProductInventory.LocationID)
  FROM Production.Product
      INNER JOIN Production.ProductInventory
      ON Production.Product.ProductID = Production.ProductInventory.ProductID;
  
• MPMediaPropertyPredicate - filter MPMediaQuery by songs duration

  I am fetching music tracks from user's music library like this:

      let query = MPMediaQuery.songs()
      let predicate = MPMediaPropertyPredicate(value: false, forProperty: MPMediaItemPropertyIsCloudItem)
      
      query.addFilterPredicate(predicate)
      
      if let fetchedSongs = query.items {
         // Do something with tracks
      }
  

  However, I don't need songs longer than 5 minutes. I tried to add a new predicate MPMediaPropertyPredicate to filter out all tracks longer than 5 minutes but with no success - I am not sure what to use in the value parameter and if I can use a condition like "duration < 300" in a simple NSPredicate.
• Value of type [ViewModel] has no member nsPredicate

  I have a list of bookmarks stored with Core Data that i want to search through. But i'm getting this error next to vm.myBookmarks.nsPredicate = NSPredicate(value: true) in 'var query' below.

  Value of type '[MyBookmarkViewModel]' has no member 'nsPredicate'

  @ObservedObject var vm : MyBookmarksViewModel
  @State private var searchText = ""
  
    ForEach(vm.myBookmarks) { myBookmark in
  
                      Text(myBookmark.name)
                      Text(myBookmark.url)          
              }
                  .searchable(text: query)
  
  
  var query: Binding<String> {
      Binding {
          searchText
      } set: { newValue in
          searchText = newValue
          if newValue.isEmpty {
              vm.myBookmarks.nsPredicate = NSPredicate(value: true)
          } else {
              vm.myBookmarks.nsPredicate = NSPredicate(format: "name CONTAINS[cd] %@", newValue)            }
      }
  }
  
  
        
  

  MyBookmarksViewModel

  class MyBookmarksViewModel: NSObject, ObservableObject {
      
      @Published var myBookmarks = [MyBookmarkViewModel]()
  
      private let fetchedResultsController: NSFetchedResultsController<MyBookmark>
      private var context: NSManagedObjectContext
      
      init(context: NSManagedObjectContext){
          self.context = context
          self.fetchedResultsController = NSFetchedResultsController(fetchRequest: MyBookmark.all  , managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
          super.init()
          fetchedResultsController.delegate = self
          fetchAll()
          
          }
  
  private func fetchAll() {
      do {
          try fetchedResultsController.performFetch()
          guard let myBookmarks = fetchedResultsController.fetchedObjects else {
              return
          }
          self.myBookmarks = 
  
  myBookmarks.map(MyBookmarkViewModel.init)
              
          } catch {
              print(error)
          }
      }
      
  }
  
  extension MyBookmarksViewModel: NSFetchedResultsControllerDelegate {
      func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
          guard let myBookmarks = controller.fetchedObjects as? [MyBookmark] else {
              return
          }
          self.myBookmarks = myBookmarks.map(MyBookmarkViewModel.init)
      }
  }
  

  MyBookmarkViewModel

  struct MyBookmarkViewModel: Identifiable, Hashable{
      
      init(myBM: MyBookmark) {
          self.myBM = myBM
          
      }
      private let myBM: MyBookmark
      
      var id: NSManagedObjectID {
          myBM.objectID
      }
      
      var name: String {
          myBM.name ?? ""
      }
  }
  

  MyBookmark

  @objc(MyBookmark)
  public class MyBookmark: NSManagedObject, BaseModel {
      static var all: NSFetchRequest<MyBookmark> {
          let request: NSFetchRequest<MyBookmark> = MyBookmark.fetchRequest()
          request.sortDescriptors = []
          return request
      }
      
  }
  
  
  extension MyBookmark {
  
      @nonobjc public class func fetchRequest() -> NSFetchRequest<MyBookmark> {
          return NSFetchRequest<MyBookmark>(entityName: "MyBookmark")
      }
  
      @NSManaged public var name: String?
      @NSManaged public var url: String?
  
  }
  
  extension MyBookmark : Identifiable {
  
  }
  

  This is for a macOS app.
• Building a conditional expression using the Mapbox iOS SDK

  I'm updating an existing iOS app that uses the Mapbox v6 SDK. The app defines a shape source using an array of point features and specifies that the points should be clustered based on a particular radius. Here's the code to do this:

  let source = MGLShapeSource(identifier: sourceIdentifier, features: features, options: [.clustered: true, .clusterRadius: 50.0, .maximumZoomLevelForClustering: 14.0])
  

  I also have a circle style layer defined to show the clusters on the map:

  let circularClusterLayer = MGLCircleStyleLayer(identifier: "clusteredMarkers", source: source)
  circularClusterLayer.predicate = NSPredicate(format: "cluster == YES")
  

  This is working as expected but now I need to define the circle color based on an attribute of all the features located in the cluster. Specifically, each of my features has a boolean property in its attributes dictionary called .needsHelp. I'm trying to define the circle color for the cluster marker based on this logic:

  if any of the features in the cluster have .needsHelp == true {
      // set the circle color = UIColor.red
      circularClusterLayer.circleColor = NSExpression(forConstantValue: UIColor.red)
  } else {
      // set the circle color = UIColor.gray
      circularClusterLayer.circleColor = NSExpression(forConstantValue: UIColor.gray)
  }
  

  I'm pretty sure that I should be able to build an expression that returns true if any of the features in the cluster have .needsHelp == true or otherwise, returns false. And I believe this expression would be assigned to the .clusterProperties option for the source like this:

  let expression1 = NSExpression(mglJSONObject: ["any",  ["==", ["boolean", ["get", "isInEmergency"]], true]])
  let expression2 = NSExpression(forConstantValue: UIColor.red)
  let clusterPropertyDictionary: NSDictionary = ["clusterContainsFeatureThatNeedsHelp" : [expression1, expression2]]        
  let selectedContactsSource = MGLShapeSource(identifier: sourceIdentifier, features: features, options: [.clustered: true, .clusterRadius: 50.0, .maximumZoomLevelForClustering: 14.0, .clusterProperties: clusterPropertyDictionary])
  

  I've been looking at the Mapbox expressions guide and I think I should be using the "any" decision expression to get a boolean value back indicating whether any of the features have .needsHelp == true or not. But so far I've been unable to translate the LISP-like expression syntax into an NSExpression that works.

  I'm assuming that in addition to the expression above, I will also need another expression to check the value of "clusterContainsFeatureThatNeedsHelp" and then set the circle color accordingly. My best guess is that that would look something like this:

  // TODO: check value of clusterContainsFeatureThatNeedsHelp to determine circle color
  
  circularClusterLayer.circleColor = NSExpression(forConditional: NSPredicate(format: "%K == %@", "clusterContainsFeatureThatNeedsHelp", NSNumber(value: true)), trueExpression: NSExpression(forConstantValue: UIColor.red), falseExpression: NSExpression(forConstantValue: UIColor.gray))
  

  Unfortunately, I'm not having any luck building either of these NSExpressions successfully. Has anyone done something like this before? If so, I'd appreciate any tips or suggestions!
• CoreData Fetch: Getting the objects with the maximum of one atttribute and having another attribute in common

  I have a CoreData ManagedObject type Event with the properties name:Sting and date:Date.

  I want to fetch all EventObject, with the name containing a filter. If more than one object with the same name matches the filter, only the object with the latest date should be returned.

  Just to clarify what I want. In a table based approach I would query in SQL like:

  SELECT name, max(date) FROM Event
  WHERE name contains 'filter'
  GROUP BY name  
  

  In CoreData I tried like this, but got:
  Could not cast value of type 'NSKnownKeysDictionary1' to 'xx12.Event'.

  let fetchRequest : NSFetchRequest<Event> = Event.fetchRequest(    fetchRequest.predicate = NSPredicate (format: "name contains %@", filter)
  fetchRequest.sortDescriptors = [NSSortDescriptor (key: "name", ascending: true)]
     
  // We want Event not Dictionary back 
  // fetchRequest.resultType = NSFetchRequestResultType.dictionaryResultType
        
  let keypathExpression = NSExpression(forKeyPath: "date")
  let maxExpression = NSExpression(forFunction: "max:", arguments: [keypathExpression])
  
  let key = "maxDate"   
  let expressionDescription = NSExpressionDescription()
  expressionDescription.name = key
  expressionDescription.expression = maxExpression
  expressionDescription.expressionResultType = .dateAttributeType
  
  fetchRequest.propertiesToFetch = [expressionDescription]
        
  let resultEvents = try moc.fetch(fetchRequest)
  

  Example:
  if I have these objects

  meeting1, 1.1.2020
  meeting1, 1.4.2020
  meeting2, 1.1.2020
  meeting2, 1.4.2020
  party, 2.3.2020
  

  and the filter: meeting
  I want to get the objects:

  meeting1, 1.4.2020
  meeting2, 1.4.2020