2D array remove First not Smooth updating tableview

Question

I have 2D array var students = [[Student]] I need to conform this array should be keep always 3 in memory so when this array insert new itme then remove from old from top

I have to insert array this way

self.students.append(student) //Update students  property

and trying with this line but tableview not update smoothly when I remove item using this line

self.students.removeFirst()

so what How can I remove array item from top for table view smoothly scrolling

Note array hooked table view

func numberOfSections(in tableView: UITableView) -> Int {
    return self.students.count
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return students[section].count
}

Update :

Possible duplicate of How to remove an element from an array in Swift — David Pasztor
– David Pasztor, Commented Aug 1, 2017 at 13:46
@Larme tableview not update smoothly when I remove item using self.students.removeFirst() — Nazmul Hasan
– Nazmul Hasan, Commented Aug 1, 2017 at 13:47
@DávidPásztor tableview not update smoothly when I remove item using self.students.removeFirst() — Nazmul Hasan
– Nazmul Hasan, Commented Aug 1, 2017 at 13:50
@NazmulHasan then why didn't you ask about smooth updating? Without editing your question to reflect your actual problem, it is a duplicate. — David Pasztor
– David Pasztor, Commented Aug 1, 2017 at 13:51

Sergey Kalinichenko · Accepted Answer · 2017-08-01 14:00:51Z

2

With a fixed upper size, you would be better off not removing items at all.

Use a fixed-size array of three items, some of which could be empty, and a separate count and firstIndex variables. Effectively, your array becomes a Circular Queue:

var students : [[Student]] = [[], [], []]
var count = 0;
var firstIndex = 0;
// Adding a new item
students[(firstIndex+count) % students.count] = newItem
if (count != 3) {
    count++
} else {
    firstIndex = (firstIndex+1) % students.count
}
// Iterating the array
for var i in (0..<students.count) {
    let currentStudent = students[(firstIndex+i)%students.count]
    ...
}

The number of sections is count:

func numberOfSections(in tableView: UITableView) -> Int {
    return count
}

The only trick is to figure out which index to use for a given index path:

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return students[(section + firstRow) % students.count].count
}

let actualIndex = (indexPath.section + firstIndex) % students.count

answered Aug 1, 2017 at 14:00

Sergey Kalinichenko

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15 Comments

Nazmul Hasan Over a year ago

Thank you so much I am trying with your answer in my project and get back you

Nazmul Hasan Over a year ago

it is working fine but when trying to append 4th item to the a array then flowing Line (firstIndex+count) % students.count give me log 3 is fatal error: Index out of range

Sergey Kalinichenko Over a year ago

@NazmulHasan This tells me that students.count is above 3, which should never happen, because students.count is fixed at 3, and any positive number mod % 3 is 0, 1, or 2. append should be replaced with the circular addition code above.

Nazmul Hasan Over a year ago

thanks basically it is working fine from 1 to 3 but when adding 4th item to the array then tableView scrolling not goes down so not showing 4th item on the other hand log see array data updated . you can check my question update section image and sample code github.com/nazmulkp/PagginationSwift3

Sergey Kalinichenko Over a year ago

@NazmulHasan I thought you wanted to cap the number of elements to three. When you add element four, element one should disappear, right? If you want scrolling to continue fine, you should tell UITableView that you are deleting rows in the entire section zero by calling deleteRowsAtIndexPaths. After that you need to tell UITableView that you are inserting a bunch of rows at the third section (section index 2). This way you would be able to avoid reloading the whole table, disrupting the scroll.

|

João Fernandes · Accepted Answer · 2017-08-01 13:58:06Z

1

Use students.removeFirst()for removing the first element and students.removeLast() for removing the last element.

If you want to remove it at a certain index use, students.remove(at: theindexyouwant)

EDIT:

If you want animation during the delete use: tableview.deleteRowsAtIndexPaths(tRemove, withRowAnimation: .Left)

edited Aug 1, 2017 at 13:58

answered Aug 1, 2017 at 13:50

João Fernandes

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2 Comments

Nazmul Hasan Over a year ago

tableview not update smoothly when I remove item using self.students.removeFirst()

Nazmul Hasan Over a year ago

tableview.deleteRowsAtIndexPaths should not work because it is 2D array

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