I am working in array handling , the overall working of the application is the user can select the number of number of songs that has to be added to a particular playlist. I have used Tableview to list the songs when the user click the tableview cell have added .checkmark when already checkmark found I will remove .checkmark, similarly when the user select the song I have kept a array to save the track id of that particular song .
"SongIDArray" is the array used to save. When the user deselect the song I have to delete the particular songs "track id". but in array it has remove(at: index) I cannot delete it through index. please help me
for example :** my array is**
songIDArray = [25,45,69,78,63]
I need to remove 78 from the index without knowing the index path.
You can use filter to remove values from an array:
let newArray = [25, 45, 69, 78, 63].filter { $0 != 78 }
removeAll is the command for conditionally removing.
var array = [25,45,69,78,63]
array.removeAll{$0 == 78}
print(array)
//[25, 45, 69, 63]
You have a few options here, whichever is best suited to your exact use-case!
Remove by filtering
The filter function passes each element in the array to the block of code you provide and removes all items you return false for. This is useful for performing a simple filter, but if you also need the index of the removed item (For example to reload a table view index path) it's not very useful.
songIDArray = songIDArray.filter({ id in
return id != 78
})
Remove by index
First get the index to remove at, you can do this in various ways depending on the type of items you have in your array. If they conform to Equatable (Integers do) you can use
if let removalIndex = songIDArray.firstIndex(of: 78) {
songIDArray.remove(at: removalIndex)
}
If you don't have an array of Equatable elements, then you can instead use index(where:) which returns the first index for which you return true from the provided closure:
if let removalIndex = songIDArray.index(where: { id in
return id == 78
}) {
songIDArray.remove(at: removalIndex)
}
This method is useful if you also need to do something else with the index, like reload a UITableViewCell at a specific index path to reflect your change e.t.c.
Remove All
In swift 4.2 there is also a removeAll(where:) function which works similar to filter but doesn't return a new array:
songIDArray.removeAll(where: { id in
return id == 78
})
Related
I have the two lists of AddItem objects. AddItem is a custom object made of data downloaded from the web. The second one list is also AddItem, but this one is saved in the database. I use it to create another list, but in this case user of the app decides which object are important for him.
This want I want to achieve is to mark every single object of the first AddItem list (not saved in the database, create during the start of the view), to show in the TableView which one is saved in the database, so I already use him in another view. You know what I mean. There is a TableView list and if I am interested in a cell I select it and add it to the database.
I hope I have described it clearly. If not, ask for questions.
The first AddItem list (not saved in the database):
func setAddItemList(stations: [Station], sensors: [Sensor]) {
var addItems = [AddItem]()
var sensorItems = [SensorItem]()
let falseValue = RealmOptional<Bool>(false)
addList = try persistenceService.fetchAddItems().toArray(ofType: AddItem.self) //The second list with saved data in the database
let addItem = stations.map { station in
AddItem(
id: station.id,
stationId: station.id,
cityName: station.city?.name ?? "",
addressStreet: station.addressStreet!,
added: falseValue,
sensor: [])
}
addItems.append(contentsOf: addItem)
As you can see, it's create by already downloaded data. I decided to add the property - added, which is the bool property and mark it as true if selected the right cell. Unfortunately I don't know how to do this when creating a list of AddItem objects. The saved array is almost the same. There is only more data, but ids, names, addresses and so on are same, so there are loads of the same data for comparison
I made the solution myself:
addItem.forEach { item in
guard let index = addList2.firstIndex(where: { $0.id == item.id})
else {
print("Failed to find the SavedAddItem for the AddItem \(item.id)")
return
}
addItems[index + 1].added = trueValue
}
I have received an array index out of range error. I have two arrays cardsCurrentlyInPlay and currentCardsSelected. Every card that is in this game has a unique ID. I am attempting to find find the index of the card in cardsCurrentlyInPlay whose cardID matches the cardID of the card in currentCardsSelected. I am doing this by using the index(where:) method that takes a closure. My closure just checks if the IDs match, they obviously match because I am using the ! to unwrap them and the app does not crash there. It seems as though the index(where:) method is returning the wrong index. I have looked at this for hours and I do not understand whats going on.
Heres the code:
let indexOfFirstCard = cardsCurrentlyInPlay.index(where: ({($0?.cardID == currentCardsSelected[0].cardID)}))!
let indexOfSecondCard = cardsCurrentlyInPlay.index(where: ({($0?.cardID == currentCardsSelected[1].cardID)}))!
let indexOfThirdCard = cardsCurrentlyInPlay.index(where: ({($0?.cardID == currentCardsSelected[2].cardID)}))!
if deck.isEmpty && selectedCardsMakeASet() {
/* Remove the old cards */
cardsCurrentlyInPlay.remove(at: indexOfFirstCard)
cardsCurrentlyInPlay.remove(at: indexOfSecondCard)
cardsCurrentlyInPlay.remove(at: indexOfThirdCard) // where code is blowing up
currentCardsSelected.removeAll()
/* Return indicies of cards to clear from the UI */
return .deckIsEmpty(indexOfFirstCard, indexOfSecondCard, indexOfThirdCard)
}
The index you’re getting is correct when your get it, but it becomes wrong when you remove other cards. Consider:
var a = ["x", "y", "z"]
let indexOfX = a.index(of: "x")! // returns 0
let indexOfZ = a.index(of: "z")! // returns 2
a.remove(at: indexOfX) // removes "x"; now a = ["y", "z"]
a.remove(at: indexOfZ) // index 2 is now out of bounds
You could interleave the calls to index(of:) and remove(at:), but a better approach would be to remove all three cards in a single pass, something like this:
let selectedCardIDs = currentCardsSelected.map { $0.cardID }
cardsCurrentlyInPlay = cardsCurrentlyInPlay.filter { card in
!selectedCardIDs.contains(card.cardID)
}
Note that this has the added benefit of avoiding the force unwrap, a sign of sounder logic.
This is because of out of bounds.
After the first two code excuted.
cardsCurrentlyInPlay.remove(at: indexOfFirstCard) &
cardsCurrentlyInPlay.remove(at: indexOfSecondCard)
there is only one element in the cardsCurrentlyInPlay .
Then if you excute cardsCurrentlyInPlay.remove(at: indexOfThirdCard), the program will crash.
I have a comments array declared as: var comments: [String] which I populate it with some Strings and I also have a UICollectionView within which I present the comments. My code is the following when I try to delete the selected cells from the UICollectionView:
if let indexPathsForSelectedItems = collectionView.indexPathsForSelectedItems {
for indexPath in indexPathsForSelectedItems {
comments.remove(at: indexPath.item) //I have only one section
}
collectionView.deleteItems(at: indexPathsForSelectedItems)
}
The issue is that sometimes when I delete the selected items, it creates an out of bounds exception on the comments array.
However when I use the following approach (create a copy array and replace the original one with its copy) no problem occurs:
var indexes: [Int] = []
for indexPath in indexPathsForSelectedItems {
indexes.append(indexPath.item)
}
var newComments: [String] = []
for (index, comment) in comments.enumerated() {
if !indexes.contains(index) {
newComments.append(comment)
}
}
comments = newComments
Why is this happening?
I am using Swift 3 and XCode 8.2.1
Sorting
If you're not sure that indexPathsForSelectedItems are sorted in descending order, and hence always deletes the highest index first, you will eventually run into an out of bounds. Deleting an item will change the indices for all array elements with higher indices.
You probably want to use indexPathsForSelectedItems.sorted(by: >).
The code is from a book. In terms of overall app architecture (MVC), it's part of the Model. The model has two main components:
An array of tags called tags
A dictionary of tag - query called searches
The app saves these pieces of data in the NSUserDefaults (iOS defaults system) and on iCloud. The following method is called when a change in iCloud is signaled. The parameter is an instance of NSNotification.userInfo
// add, update, or delete searches based on iCloud changes
func performUpdates(userInfo: [NSObject: AnyObject?]) {
// get changed keys NSArray; convert to [String]
let changedKeysObject = userInfo[NSUbiquitousKeyValueStoreChangedKeysKey]
let changedKeys = changedKeysObject as! [String]
// get NSUbiquitousKeyValueStore for updating
let keyValueStore = NSUbiquitousKeyValueStore.defaultStore()
// update searches based on iCloud changes
for key in changedKeys {
if let query = keyValueStore.stringForKey(key) {
saveQuery(query, forTag: key, saveToCloud: false)
} else {
searches.removeValueForKey(key)
tags = tags.filter{$0 != key}
updateUserDefaults(updateTags: true, updateSearches: true)
}
delegate.modelDataChanged() // update the view
}
}
My question is on the if - else inside the for loop. The for loop iterates over keys that where changed; either the user adds a new search, updates an existing search, or deletes a search. But, I don't understand the logic behind the if-else. Some clarifying thoughts would be appreciated. I've read it over and over but it doesn't tick with me.
if let query = keyValueStore.stringForKey(key)
means that if keyValueStore contains a string corresponding to key, then this string will be assigned to the constant query.
This is called "safe unwrapping":
inside the if let ... condition, the query is safely saved with saveQuery because using if let ... guarantees that the value of keyValueStore.stringForKey(key) won't be nil.
If the value is nil, then in the else branch, the filter method is used to update the tags array without the key we just processed: tags.filter{$0 != key} means "return all items in tags that are different from key" (the $0 represents the current item from the array processed by filter).
I have a mutable array:
var responseArray = ["yes", "no", "no way", "of course", "for sure", "not a chance", "positively"]
The responseArray is the data source for my table view which allows for multiple selections during editing.
I am capturing the selected index paths:
let paths = tableView.indexPathsForSelectedRows()
I can return and verify each selected indexPath of my tableView by running println(paths).
I have read the documentation for the indexPathsForSelectedRows method and understand that it returns an array of index paths which I have sorted by row.
What I cannot understand is how I can use the returned array of index paths to remove the data from the responseArray for each row that is selected for deletion in the table view.
After reading through some documents, is it correct of me to believe that I cannot remove any data from the `responseArray' as I am enumerating over it? For example:
#IBAction func deleteButtonPressed(sender: AnyObject) {
if responseArray.count > 0 {
if let paths = self.tableView.indexPathsForSelectedRows() {
var sortedArray = paths.sorted({$0.row < $1.row})
// Remove index paths from responseArray
for i in sortedArray {
responseArray.removeAtIndex(i.row)
}
self.tableView.reloadData()
}
}
}
I am able to remove each row from the table view one by one, but when I select the first and last rows, all of the rows, or any other combination of rows for deletion, I get fatal error: Array index out of range. However, if I select two adjacent rows for deletion, the desired result is achieved and those two rows are removed from the table view.
I know that there is something that I am missing, but as a new programmer I have been unable to resolve this issue for three days now. What is it that I am not doing correctly?
Here's your array: [ A, B, C, D ]
Let's say you want to delete A and D at index 0 and 3 respectively, one at a time:
deleteAtIndex(0) gives: [ B, C, D ]
deleteAtIndex(3) gives: Out of bounds exception
Edit:
Ok, to avoid complicating things, why not just always delete the highest index first by reversing your sort: {$1.row < $0.row}
For future reference, in addition to the answers given already you could simplify it further by reversing the selected indices:
#IBAction func deleteButtonPressed(sender: AnyObject) {
self.tableView.selectedRowIndexes.reverse().forEach { x in
responseArray.removeAtIndex(x)
}
self.tableView.reloadData()
}
Since your paths array is sorted, you know that every time you delete an element from the array, higher indices will now be one less than they were. You can simply keep an incrementing offset to apply to your deletions -
#IBAction func deleteButtonPressed(sender: AnyObject) {
if responseArray.count > 0 {
if let paths = self.tableView.indexPathsForSelectedRows() {
var sortedArray = paths.sorted({$0.row < $1.row})
var offset=0;
// Remove index paths from responseArray
for i in sortedArray {
responseArray.removeAtIndex(i.row-offset)
offset++
}
self.tableView.reloadData()
}
}
}