How to delete data from SwiftUI List and Realm - ios

Question

The following code properly displays all of the 'Users' from Realm database in a SwiftUI List. My issue is deleting records when I swipe a row.
When I swipe a row and tap the delete button, I immediately get an uncaught exception error, the List does not update but I know the right item gets deleted from the Realm database since the next time I run the app the selected record doesn't show up.
Here is my code.
SwiftUI Code
import RealmSwift
struct ContentView: View {
#State private var allUsers: Results<User> = realm.objects(User.self)
var body: some View {
VStack{
Text("Second Tab")
List{
ForEach(allUsers, id:\.self) { user in
HStack{
Text(user.name)
Text("\(user.age)")
}
}.onDelete(perform: deleteRow)
}
}
}
private func deleteRow(with indexSet: IndexSet){
indexSet.forEach ({ index in
try! realm.write {
realm.delete(self.allUsers[index])
}
})
}
}
Realm Model
import RealmSwift
class User:Object{
#objc dynamic var name:String = ""
#objc dynamic var age:Int = 0
#objc dynamic var createdAt = NSDate()
#objc dynamic var userID = UUID().uuidString
override static func primaryKey() -> String? {
return "userID"
}
}
ERROR
Terminating app due to uncaught exception 'RLMException', reason: 'Index 4 is out of bounds (must be less than 4).'
Of course, the 4 changes depending on how many items are in the Realm database, in this case, I had 5 records when I swiped and tapped the delete button.
My expectation was that the List was going to update every time the allUsers #State variable changes, I know my issue is not fully understanding how binding works.
What am I doing wrong?

Answer 1

My expectation was that the List was going to update every time the
allUsers #State variable changes
It is correct, but state was not changed... The following should work
private func deleteRow(with indexSet: IndexSet){
indexSet.forEach ({ index in
try! realm.write {
realm.delete(self.allUsers[index])
}
})
self.allUsers = realm.objects(User.self) // << refetch !!
}
Note: the below is just assigning initial state value
#State private var allUsers: Results<User> = realm.objects(User.self)

Answer 2

This is a very common bug when working with Realm. It happens in ''traditional'' view controllers too.
The only solid solution I found, and it has considerably improved applications stability is to always use interface items instead of realm object.
Moreover, in real life, we need to do some processes, load avatar images from server, add some check boxes, selections or whatever, and we often don't need all properties of objects to be displayed. Somehow, it's a MVVM approach.
By the way, you can call realm.write before the loop, not sure, but I think it's good to minimise context switching.
Using this technique, either with SwiftUI or UIViewControllers, will solve RLM crashes for good.
struct ContentView: View {
struct UserItem: Hashable {
var id: String
var name: String
var age: Int
}
private var allUsers: Results<User> = realm.objects(User.self)
#State private var userItems: [UserItem] = []
func updateItems() {
userItems = allUsers.map {
UserItem(id: $0.userID, name: $0.name, age: $0.age)
}
}
var body: some View {
VStack {
Text("Second Tab")
List{
ForEach(userItems, id:\.self) { user in
HStack{
Text(user.name)
Text("\(user.age)")
}
}
.onDelete(perform: deleteRow)
}
}.onAppear() {
updateItems()
}
}
private func deleteRow(with indexSet: IndexSet){
try! realm.write {
indexSet.forEach {
realm.delete(self.allUsers[$0])
}
}
updateItems()
}
}