I would like to select from the database using a PXSelect and then receive a value that respects the segmented key.
Example:
var item = InventoryItem.PK.Find(graph, someInventoryID);
string inventoryCDRespectingSegmentedKey = SomeClass.SomeMethod(item.InventoryCD); // InventoryCD is a string value without the separators defined in the Segmented key at this point
I am not sure if this is the best way to get the value respecting segments or not, but this is how I do it usually.
if (row.InventoryID != null)
{
var item = InventoryItem.PK.Find(sender.Graph, row.InventoryID);
if (item != null)
{
var inventoryCDRespectingSegmentedKey = sender.Graph.Caches[typeof(InventoryItem)].GetValueExt<InventoryItem.inventoryCD>(item) as PXSegmentedState;
PXTrace.WriteInformation($"{inventoryCDRespectingSegmentedKey.ToString()}");
}
}
I want to change the order of the rows in a list that retrieves objects from the core data. Moving rows works, but the problem is that I can't save the changes. I don't know how to save the changed Index of the CoreData Object.
Here is my Code:
Core Data Class:
public class CoreItem: NSManagedObject, Identifiable{
#NSManaged public var name: String
}
extension CoreItem{
static func getAllCoreItems() -> NSFetchRequest <CoreItem> {
let request: NSFetchRequest<CoreItem> = CoreItem.fetchRequest() as! NSFetchRequest<CoreItem>
let sortDescriptor = NSSortDescriptor(key: "date", ascending: true)
request.sortDescriptors = [sortDescriptor]
return request
}
}
extension Collection where Element == CoreItem, Index == Int {
func move(set: IndexSet, to: Int, from managedObjectContext: NSManagedObjectContext) {
do {
try managedObjectContext.save()
} catch {
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
}
}
List:
struct CoreItemList: View {
#Environment(\.managedObjectContext) var managedObjectContext
#FetchRequest(fetchRequest: CoreItem.getAllCoreItems()) var CoreItems: FetchedResults<CoreItem>
var body: some View {
NavigationView{
List {
ForEach(CoreItems, id: \.self){
coreItem in
CoreItemRow(coreItem: coreItem)
}.onDelete {
IndexSet in let deleteItem = self.CoreItems[IndexSet.first!]
self.managedObjectContext.delete(deleteItem)
do {
try self.managedObjectContext.save()
} catch {
print(error)
}
}
.onMove {
self.CoreItems.move(set: $0, to: $1, from: self.managedObjectContext)
}
}
.navigationBarItems(trailing: EditButton())
}.navigationViewStyle(StackNavigationViewStyle())
}
}
Thank you for help.
Caveat: the answer below is untested, although I used parallel logic in a sample project and that project seems to be working.
There's a couple parts to the answer. As Joakim Danielson says, in order to persist the user's preferred order you will need to save the order in your CoreItem class. The revised class would look like:
public class CoreItem: NSManagedObject, Identifiable{
#NSManaged public var name: String
#NSManaged public var userOrder: Int16
}
The second part is to keep the items sorted based on the userOrder attribute. On initialization the userOrder would typically default to zero so it might be useful to also sort by name within userOrder. Assuming you want to do this, then in CoreItemList code:
#FetchRequest( entity: CoreItem.entity(),
sortDescriptors:
[
NSSortDescriptor(
keyPath: \CoreItem.userOrder,
ascending: true),
NSSortDescriptor(
keyPath:\CoreItem.name,
ascending: true )
]
) var coreItems: FetchedResults<CoreItem>
The third part is that you need to tell swiftui to permit the user to revise the order of the list. As you show in your example, this is done with the onMove modifier. In that modifier you perform the actions needed to re-order the list in the user's preferred sequence. For example, you could call a convenience function called move so the modifier would read:
.onMove( perform: move )
Your move function will be passed an IndexSet and an Int. The index set contains all the items in the FetchRequestResult that are to be moved (typically that is just one item). The Int indicates the position to which they should be moved. The logic would be:
private func move( from source: IndexSet, to destination: Int)
{
// Make an array of items from fetched results
var revisedItems: [ CoreItem ] = coreItems.map{ $0 }
// change the order of the items in the array
revisedItems.move(fromOffsets: source, toOffset: destination )
// update the userOrder attribute in revisedItems to
// persist the new order. This is done in reverse order
// to minimize changes to the indices.
for reverseIndex in stride( from: revisedItems.count - 1,
through: 0,
by: -1 )
{
revisedItems[ reverseIndex ].userOrder =
Int16( reverseIndex )
}
}
Technical reminder: the items stored in revisedItems are classes (i.e., by reference), so updating these items will necessarily update the items in the fetched results. The #FetchedResults wrapper will cause your user interface to reflect the new order.
Admittedly, I'm new to SwiftUI. There is likely to be a more elegant solution!
Paul Hudson (Hacking With Swift) has quite a bit more detail. Here is a link for info on moving data in a list. Here is a link for using core data with SwiftUI (it involves deleting items in a list, but is closely analogous to the onMove logic)
Below you can find a more generic approach to this problem. The algorithm minimises the number of CoreData entities that require an update, to the contrary of the accepted answer. My solution is inspired by the following article: https://www.appsdissected.com/order-core-data-entities-maximum-speed/
First I declare a protocol as follows to use with your model struct (or class):
protocol Sortable {
var sortOrder: Int { get set }
}
As an example, assume we have a SortItem model which implements our Sortable protocol, defined as:
struct SortItem: Identifiable, Sortable {
var id = UUID()
var title = ""
var sortOrder = 0
}
We also have a simple SwiftUI View with a related ViewModel defined as (stripped down version):
struct ItemsView: View {
#ObservedObject private(set) var viewModel: ViewModel
var body: some View {
NavigationView {
List {
ForEach(viewModel.items) { item in
Text(item.title)
}
.onMove(perform: viewModel.move(from:to:))
}
}
.navigationBarItems(trailing: EditButton())
}
}
extension ItemsView {
class ViewModel: ObservableObject {
#Published var items = [SortItem]()
func move(from source: IndexSet, to destination: Int) {
items.move(fromOffsets: source, toOffset: destination)
// Note: Code that updates CoreData goes here, see below
}
}
}
Before I continue to the algorithm, I want to note that the destination variable from the move function does not contain the new index when moving items down the list. Assuming that only a single item is moved, retrieving the new index (after the move is complete) can be achieved as follows:
func move(from source: IndexSet, to destination: Int) {
items.move(fromOffsets: source, toOffset: destination)
if let oldIndex = source.first, oldIndex != destination {
let newIndex = oldIndex < destination ? destination - 1 : destination
// Note: Code that updates CoreData goes here, see below
}
}
The algorithm itself is implemented as an extension to Array for the case that the Element is of the Sortable type. It consists of a recursive updateSortOrder function as well as a private helper function enclosingIndices which retrieves the indices that enclose around a certain index of the array, whilst remaining within the array bounds. The complete algorithm is as follows (explained below):
extension Array where Element: Sortable {
func updateSortOrder(around index: Int, for keyPath: WritableKeyPath<Element, Int> = \.sortOrder, spacing: Int = 32, offset: Int = 1, _ operation: #escaping (Int, Int) -> Void) {
if let enclosingIndices = enclosingIndices(around: index, offset: offset) {
if let leftIndex = enclosingIndices.first(where: { $0 != index }),
let rightIndex = enclosingIndices.last(where: { $0 != index }) {
let left = self[leftIndex][keyPath: keyPath]
let right = self[rightIndex][keyPath: keyPath]
if left != right && (right - left) % (offset * 2) == 0 {
let spacing = (right - left) / (offset * 2)
var sortOrder = left
for index in enclosingIndices.indices {
if self[index][keyPath: keyPath] != sortOrder {
operation(index, sortOrder)
}
sortOrder += spacing
}
} else {
updateSortOrder(around: index, for: keyPath, spacing: spacing, offset: offset + 1, operation)
}
}
} else {
for index in self.indices {
let sortOrder = index * spacing
if self[index][keyPath: keyPath] != sortOrder {
operation(index, sortOrder)
}
}
}
}
private func enclosingIndices(around index: Int, offset: Int) -> Range<Int>? {
guard self.count - 1 >= offset * 2 else { return nil }
var leftIndex = index - offset
var rightIndex = index + offset
while leftIndex < startIndex {
leftIndex += 1
rightIndex += 1
}
while rightIndex > endIndex - 1 {
leftIndex -= 1
rightIndex -= 1
}
return Range(leftIndex...rightIndex)
}
}
First, the enclosingIndices function. It returns an optional Range<Int>. The offset argument defines the distance for the enclosing indices left and right of the index argument. The guard ensures that the complete enclosing indices are contained within the array. Further, in case the offset goes beyond the startIndex or endIndex of the array, the enclosing indices will be shifted to the right or left, respectively. Hence, at the boundaries of the array, the index is not necessarily located in the middle of the enclosing indices.
Second, the updateSortOrder function. It requires at least the index around which the update of the sorting order should be started. This is the new index from the move function in the ViewModel. Further, the updateSortOrder expects an #escaping closure providing two integers, which will be explained below. All other arguments are optional. The keyPath is defaulted to \.sortOrder in conformance with the expectations from the protocol. However, it can be specified if the model parameter for sorting differs. The spacing argument defines the sort order spacing that is typically used. The larger this value, the more sort operations can be performed without requiring any other CoreData update except for the moved item. The offset argument should not really be touched and is used in the recursion of the function.
The function first requests the enclosingIndices. In case these are not found, which happens immediately when the array is smaller than three items or either inside one of the recursions of the updateSortOrder function when the offset is such that it would go beyond the boundaries of the array; then the sort order of all items in the array are reset in the else case. In that case, if the sortOrder differs from the items existing value, the #escaping closure is called. It's implementation will be discussed further below.
When the enclosingIndices are found, both the left and right index of the enclosing indices not being the index of the moved item are determined. With these indices known, the existing 'sort order' values for these indices are obtained through the keyPath. It is then verified if these values are not equal (which could occur if the items were added with equal sort orders in the array) as well as if a division of the difference between the sort orders and the number of enclosing indices minus the moved item would result in a non-integer value. This basically checks whether there is a place left for the moved item's potentially new sort order value within the minimum spacing of 1. If this is not the case, the enclosing indices should be expanded to the next higher offset and the algorithm run again, hence the recursive call to updateSortOrder in that case.
When all was successful, the new spacing should be determined for the items between the enclosing indices. Then all enclosing indices are looped through and each item's sorting order is compared to the potentially new sorting order. In case it changed, the #escaping closure is called. For the next item in the loop the sort order value is updated again.
This algorithm results in the minimum amount of callbacks to the #escaping closure. Since this only happens when an item's sort order really needs to be updated.
Finally, as you perhaps guessed, the actual callbacks to CoreData will be handled in the closure. With the algorithm defined, the ViewModel move function is then updated as follows:
func move(from source: IndexSet, to destination: Int) {
items.move(fromOffsets: source, toOffset: destination)
if let oldIndex = source.first, oldIndex != destination {
let newIndex = oldIndex < destination ? destination - 1 : destination
items.updateSortOrder(around: newIndex) { [weak self] (index, sortOrder) in
guard let self = self else { return }
var item = self.items[index]
item.sortOrder = sortOrder
// Note: Callback to interactor / service that updates CoreData goes here
}
}
}
Please let me know if you have any questions regarding this approach. I hope you like it.
Had a problem with Int16 and solved it by changing it to #NSManaged public var userOrder: NSNumber? and in the func: NSNumber(value: Int16( reverseIndex ))
As well I needed to add try? managedObjectContext.save() in the func to actually save the new order.
Now its working fine - thanks!
I'm not sure using a CoreData NSManagedObject for a view model object is the best approach, but if you do below is a sample for moving items in a SwiftUI List and persisting an object value based sort order.
An UndoManager is used in the event an error occurs during the move to rollback any changes.
class Note: NSManagedObject {
#nonobjc public class func fetchRequest() -> NSFetchRequest<Note> {
return NSFetchRequest<Note>(entityName: "Note")
}
#NSManaged public var id: UUID?
#NSManaged public var orderIndex: Int64
#NSManaged public var text: String?
}
struct ContentView: View {
#Environment(\.editMode) var editMode
#Environment(\.managedObjectContext) var viewContext
#FetchRequest(sortDescriptors:
[NSSortDescriptor(key: "orderIndex", ascending: true)],
animation: .default)
private var notes: FetchedResults<Note>
var body: some View {
NavigationView {
List {
ForEach (notes) { note in
Text(note.text ?? "")
}
}
.onMove(perform: moveNotes)
}
.navigationTitle("Notes")
.toolbar {
ToolbarItem(placement: .navigationBarTrailing) {
EditButton()
}
}
}
func moveNotes(_ indexes: IndexSet, _ i: Int) {
guard
1 == indexes.count,
let from = indexes.first,
from != i
else { return }
var undo = viewContext.undoManager
var resetUndo = false
if undo == nil {
viewContext.undoManager = .init()
undo = viewContext.undoManager
resetUndo = true
}
defer {
if resetUndo {
viewContext.undoManager = nil
}
}
do {
try viewContext.performAndWait {
undo?.beginUndoGrouping()
let moving = notes[from]
if from > i { // moving up
notes[i..<from].forEach {
$0.orderIndex = $0.orderIndex + 1
}
moving.orderIndex = Int64(i)
}
if from < i { // moving down
notes[(from+1)..<i].forEach {
$0.orderIndex = $0.orderIndex - 1
}
moving.orderIndex = Int64(i)
}
undo?.endUndoGrouping()
try viewContext.save()
}
} catch {
undo?.endUndoGrouping()
viewContext.undo()
// TODO: something with the error
// set a state variable to display the error condition
fatalError(error.localizedDescription)
}
}
}
if do like this
.onMove {
self.CoreItems.move(set: $0, to: $1, from: self.managedObjectContext)
try? managedObjectContext.save()
I have the following problem definition:
Design a lock-free simple linked list with the following operations:
Add(item): add the node to the beginning (head) of the list
Remove(item): remove the given item from the list
Below is shown the code implemented so far:
public class List<T>
{
private readonly T _sentinel;
private readonly Node<T> _head;
public List()
{
_head = new Node<T>();
_sentinel = default(T);
}
public List(T item)
{
_head = new Node<T>(item);
_sentinel = item;
}
public void Add(T item)
{
Node<T> node = new Node<T>(item);
do
{
node.Next = _head.Next;
}
while (!Atomic.CAS(ref _head.Next, node.Next, node));
}
public void Remove(Node<T> item)
{
Node<T> next;
Node<T> oldItem = item;
if (item.Value.Equals(_sentinel))
return;
item.Value = _sentinel;
do
{
next = item.Next;
if (next == null)
{
Atomic.CAS(ref item.Next, null, null);
return;
}
} while (!Atomic.CAS(ref item.Next, next, next.Next));
item.Value = next.Value;
}
}
The head is actually a dummy (sentinel) node kept for ease of use. The practical head is actually _head.Next.
The problem is on the remove operation when trying to remove the last element of the list:
On the remove part there are two cases:
The node has a following not-null next pointer: then do the CAS operation and steal the value data of the next item removing actually the next item
The problematic case is when the element to remove is the last one in the list:
Do Atomically: If (item == oldItem and item.Next == null) then item = null where oldItem is a pointer to the item to remove;
So I want to do is in the case of removing C node:
if(C==old-C-reference and C.Next == null) then C = null => all atomically
The problem is that I have a CAS only on a single object.
How can I solve this problem atomically? Or is there a better way of doing this remove operation that I'm missing out here?
when removing B we do a trick by copying C's contents to B and removing C: B.Next = C.Next (in the loop) and B.Value = C.Value after the move succeeded
So you need to atomically modify two memory locations. CAS in .NET does not support that. You can, however, wrap those two values in another object that can be swapped out atomically:
class ValuePlusNext<T> {
T Value;
Node<T> Next;
}
class Node<T> {
ValuePlusNext<T> Value;
}
Now you can write to both values in one atomic operation. CAS(ref Value, new ValuePlusNext<T>(next.Value, next.Value.Next). Something like that.
It is strange that ValuePlusNext has the same structure that your old Node class had. In a sense you are now managing two physical linked list node for each logical one.
while (true) {
var old = item.Value;
var new = new ValuePlusNext(...);
if (CAS(ref Value, old, new)) break;
}
I would like to get a list of most possible list of tokens for a given location in the text (line and column number) to determine what has to be populated for auto code completion. Can this be easily achieved using ANTLR 4 API.
I want to get the possible list of tokens for a given location because the user might be writing/editing somewhere in the middle of the text which still guarantees the possible list of tokens.
Please give me some guidelines because I was unable to find an online resource on this topic.
One way to get tokens by line number is to create a ParseTreeListener for your grammar, use it to walk a given ParseTree and index TerminalNodes by line number. I don't know C#, but here is how I've done it in Java. Logic should be similar.
public class MyLineIndexer extends MyGrammarParserBaseListener {
protected MultiMap<Integer, TerminalNode> filelineTokenIndex;
#Override
public void visitTerminal(#NotNull TerminalNode node) {
// map every token to its file line for searching later...
if ( node.getSymbol() != null ) {
List<TerminalNode> tokens;
Integer line = node.getSymbol().getLine();
if (!filelineTokenIndex.containsKey(line)) {
tokens = new ArrayList<>();
filelineTokenIndex.put(line, tokens);
} else {
tokens = filelineTokenIndex.get(line);
}
tokens.add(node);
}
super.visitTerminal(node);
}
}
then walk the parse tree the usual way...
ParseTree parseTree = ... ; // parse it how you want to
MyLineIndexer indexer = new MyLineIndexer();
ParseTreeWalker walker = new ParseTreeWalker();
walker.walk(indexer, parseTree);
Getting the token at a line and range is now reasonably straight forward and efficient assuming you have a reasonable number of tokens on a line. For example you can add another method to the Listener like this:
public TerminalNode findTerminalNodeAtCaret(int caretPos, int caretLine) {
if (caretPos <= 0) return null;
if (this.filelineTokenIndex.containsKey(caretLine)) {
List<TerminalNode> nodes = filelineTokenIndex.get(caretLine);
if (nodes.size() == 0) return null;
int tokenEndPos, tokenStartPos;
for (TerminalNode n : nodes) {
if (n.getSymbol() != null) {
tokenEndPos = n.getSymbol().getCharPositionInLine() + n.getText().length();
tokenStartPos = n.getSymbol().getCharPositionInLine();
// If the caret is within this token, return this token
if (caretPos >= tokenStartPos && caretPos <= tokenEndPos) {
return n;
}
}
}
}
return null;
}
You will also need to ensure your parser allows for 'loose' parsing. While a language construct is being typed, it is likely not to be valid. Your Parser rules should allow for this.
I am creating one J2ME application which read/write RMS record. I able to read and write
record in RMS but now problem is that I want to delete record by accepting some value
like accountNumber.
Format of RMS record.
101,ABC,12345,12345
and String str contain following data.
String str=accountSrNumber +","+ name +","+ balance +","+ TextDeposit;
deleteRecStore(str,accountSrNumber);
And I need to accept accountNumber(101) from user and need to delete this record.
Here is my Delete method.
public void deleteRecStore(String str, String accNumber121) //
{
int s=str.indexOf(accNumber121);
System.out.println("index in delete function"+s);
if(s==0)
{
try{
rs.deleteRecord(s);
// RecordStore.deleteRecordStore(REC_STORE);
System.out.println("record delete successfully");
}
catch (Exception e)
{}
}
}
I tried to use both of method rs.deleteRecord(s) and RecordStore.deleteRecordStore(REC_STORE);.
But none helps.
You always delete record 0 which is the first record, which is a bad idea.
For example, if you add two records, and delete them, and than add another record, it will be indexed as 2, so you will have to call deleteRecord(2) to remove it.
Method deleteRecordStore() removes entire recordStore (which contains records) - after that, if you create one, the next added record will be indexed as zero.
If I got the idea, you want to delete a record by it's acoountNumber.
If i'm right, you need to find the recordID by it's contents. The code will probably look like this (may have mistakes, did not test it, but the idea is important):
public void deleteRecStore(String accNumber121) {
RecordEnumeration e = rs.enumerateRecords();
int found = -1;
while (e.hasMoreElements()) {
int id = e.nextRecordId();
String next = new String(e.nextRecord());
if (next.startsWidth(accNumber121)) {
found = id;
}
}
if (found == -1) {
System.out.println("not found!");
} else {
rs.deleteRecord(found);
}
}