UITableView load more when scrolling to bottom like Facebook application

Question

I am developing an application that uses SQLite. I want to show a list of users (UITableView) using a paginating mechanism. Could any one please tell me how to load more dat

Answer 1

Swift

Method 1: Did scroll to bottom

Here is the Swift version of Pedro Romão's answer. When the user stops scrolling it checks if it has reached the bottom.

func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {

    // UITableView only moves in one direction, y axis
    let currentOffset = scrollView.contentOffset.y
    let maximumOffset = scrollView.contentSize.height - scrollView.frame.size.height

    // Change 10.0 to adjust the distance from bottom
    if maximumOffset - currentOffset <= 10.0 {
        self.loadMore()
    }
}

Method 2: Reached last row

And here is the Swift version of shinyuX's answer. It checks if the user has reached the last row.

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    // set up cell
    // ...

    // Check if the last row number is the same as the last current data element
    if indexPath.row == self.dataArray.count - 1 {
        self.loadMore()
    }

}

Example of a loadMore() method

I set up these three class variables for fetching batches of data.

// number of items to be fetched each time (i.e., database LIMIT)
let itemsPerBatch = 50

// Where to start fetching items (database OFFSET)
var offset = 0

// a flag for when all database items have already been loaded
var reachedEndOfItems = false

This is the function to load more items from the database into the table view.

func loadMore() {

    // don't bother doing another db query if already have everything
    guard !self.reachedEndOfItems else {
        return
    }

    // query the db on a background thread
    DispatchQueue.global(qos: .background).async {

        // determine the range of data items to fetch
        var thisBatchOfItems: [MyObjects]?
        let start = self.offset
        let end = self.offset + self.itemsPerBatch

        // query the database
        do {
            // SQLite.swift wrapper
            thisBatchOfItems = try MyDataHelper.findRange(start..<end)
        } catch _ {
            print("query failed")
        }

        // update UITableView with new batch of items on main thread after query finishes
        DispatchQueue.main.async {

            if let newItems = thisBatchOfItems {

                // append the new items to the data source for the table view
                self.myObjectArray.appendContentsOf(newItems)

                // reload the table view
                self.tableView.reloadData()

                // check if this was the last of the data
                if newItems.count < self.itemsPerBatch {
                    self.reachedEndOfItems = true
                    print("reached end of data. Batch count: \(newItems.count)")
                }

                // reset the offset for the next data query
                self.offset += self.itemsPerBatch
            }

        }
    }
}

Answer 2

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {

    if (news.count == 0) {
        return 0;
    } else {
        return news.count +  1 ;
    }
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    @try {

        uint position = (uint) (indexPath.row);
        NSUInteger row = [indexPath row];
        NSUInteger count = [news count];

        //show Load More
        if (row == count) {
            UITableViewCell *cell = nil;

            static NSString *LoadMoreId = @"LoadMore";
            cell = [tableView dequeueReusableCellWithIdentifier:LoadMoreId];
            if (cell == nil) {
                cell = [[UITableViewCell alloc]
                        initWithStyle:UITableViewCellStyleDefault
                      reuseIdentifier:LoadMoreId];
            }
            if (!hasMoreLoad) {
                cell.hidden = true;
            } else {

                cell.textLabel.text = @"Load more items...";
                cell.textLabel.textColor = [UIColor blueColor];
                cell.textLabel.font = [UIFont boldSystemFontOfSize:14];
                NSLog(@"Load more");
                if (!isMoreLoaded) {
                    isMoreLoaded = true;
                    [self performSelector:@selector(loadMoreNews) withObject:nil afterDelay:0.1];
                }
            }

            return cell;

        } else {
            NewsRow *cell = nil;

            NewsObject *newsObject = news[position];
            static NSString *CellIdentifier = @"NewsRow";
            cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

            if (cell == nil) {
                // Load the top-level objects from the custom cell XIB.
                NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:CellIdentifier owner:self options:nil];
                // Grab a pointer to the first object (presumably the custom cell, as that's all the XIB should contain).
                cell = topLevelObjects[0];
                // Configure the cell...

            }

            cell.title.text = newsObject.title;             
            return cell;
        }

    }
    @catch (NSException *exception) {
        NSLog(@"Exception occurred: %@, %@", exception, [exception userInfo]);
    }
    return nil;
}

very good explanation on this post.

http://useyourloaf.com/blog/2010/10/02/dynamically-loading-new-rows-into-a-table.html

simple you have to add last row and hide it and when table row hit last row than show the row and load more items.

Answer 3

Use limit and offset in your queries and fill your tableview with that content. When the user scrolls down, load the next offset.

Implement the tableView:willDisplayCell:forRowAtIndexPath: method in your UITableViewDelegate and check to see if it's the last row

Answer 4

let threshold = 100.0 // threshold from bottom of tableView
var isLoadingMore = false // flag


func scrollViewDidScroll(scrollView: UIScrollView) {
    let contentOffset = scrollView.contentOffset.y
    let maximumOffset = scrollView.contentSize.height - scrollView.frame.size.height;

    if !isLoadingMore && (maximumOffset - contentOffset <= threshold) {
        // Get more data - API call
        self.isLoadingMore = true

        // Update UI
        dispatch_async(dispatch_get_main_queue()) {
            tableView.reloadData()
            self.isLoadingMore = false
        }
    }
  }

Answer 5

I have implemented one solution that i found in stackoverflow, and it works fine, but i think the shinyuX's solution it's very easy to implement and works fine for my propose. If someone wants a different solution can use this one below.

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{

   // UITableView only moves in one direction, y axis
    CGFloat currentOffset = scrollView.contentOffset.y;
    CGFloat maximumOffset = scrollView.contentSize.height - scrollView.frame.size.height;

    //NSInteger result = maximumOffset - currentOffset;

    // Change 10.0 to adjust the distance from bottom
    if (maximumOffset - currentOffset <= 10.0) {
        [self loadOneMorePage];
        //[self methodThatAddsDataAndReloadsTableView];
    }
}

Answer 6

for loading from an API, It works for me, Xcode10 , swift 4.2 :

1- create New Swift file and do like this:

//
//  apiTVCController.swift
//  ApiTestingTableView
//
//  Created by Hooma7n on 4/7/19.
//  Copyright © 2019 Hooma7n. All rights reserved.
//

import Foundation
import Alamofire

class apiget {

    var tableData : [Datum] = []
    var loadin : [Datum] = []
    var testfortotal : Int?


    func getfromapi(completionHandler : ((_ isSucess : Bool) -> Void)?) {
        let url = "https://reqres.in/api/users?page=1"
        Alamofire.request(url, method: .get, parameters: nil, encoding: JSONEncoding.default, headers: nil)
            .responseJSON(completionHandler : { response in
                switch response.result {
                case .success(let data):
                    guard let jsonData = try? JSONSerialization.data(withJSONObject: data, options: JSONSerialization.WritingOptions.prettyPrinted) else {return}
                    let decoder = JSONDecoder()
                    guard let result = try? decoder.decode(Welcome.self, from: jsonData) else {return}
                    self.tableData = result.data ?? []
                    self.testfortotal = result.total ?? 0
                    completionHandler?(true)

                //                    print(result)
                case .failure(let error):
                    print(error)
                }
            })
    }

    var pagecounter : Int = 2


    func loadmore(completionHandler : ((_ isSucess : Bool) -> Void)?){

        let url = "https://reqres.in/api/users?page=\(pagecounter)"
        Alamofire.request(url, method: .get, parameters: nil, encoding: JSONEncoding.default, headers: nil)
            .responseJSON(completionHandler : { response in
                switch response.result {
                case .success(let data):
                    guard let jsonData = try? JSONSerialization.data(withJSONObject: data, options: JSONSerialization.WritingOptions.prettyPrinted) else {return}
                    let decoder = JSONDecoder()
                    guard let myresult = try? decoder.decode(Welcome.self, from: jsonData) else {return}
                    self.loadin = myresult.data ?? []
                    self.tableData.append(contentsOf: myresult.data ?? [])
                    completionHandler?(true)
                    print(self.pagecounter)
                    self.pagecounter += 1

                //                    print(myresult)
                case .failure(let error):
                    print(error)
                }
            })

    }

}

extension apiget {

    struct Welcome: Codable {
        let page, perPage, total, totalPages: Int?
        var data: [Datum]?

        enum CodingKeys: String, CodingKey {
            case page
            case perPage = "per_page"
            case total
            case totalPages = "total_pages"
            case data
        }
    }

    struct Datum: Codable {
        let id: Int?
        let firstName, lastName: String?
        let avatar: String?

        enum CodingKeys: String, CodingKey {
            case id
            case firstName = "first_name"
            case lastName = "last_name"
            case avatar
        }
    }


}

2- in Your ViewController file (tableView Controller) :

//
//  apiTVC.swift
//  ApiTestingTableView
//
//  Created by Hooma7n on 4/7/19.
//  Copyright © 2019 Hooma7n. All rights reserved.
//

import UIKit
import Alamofire

class apiTVC: UITableViewController {

    var datamodel = apiget()

    override func viewDidLoad() {
        super.viewDidLoad()

        datamodel.getfromapi(completionHandler: {finish in
            if finish {self.tableView.reloadData()
            }

        })

    }


    override func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return datamodel.tableData.count
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! apiTableViewCell
        cell.firstNameLabel.text = datamodel.tableData[indexPath.row].firstName
        cell.lastNameLabel.text = datamodel.tableData[indexPath.row].lastName
        cell.dateLabel.text = "\(datamodel.tableData[indexPath.row].id ?? 0)"
        cell.profileImageView.loadImage(fromURL: datamodel.tableData[indexPath.row].avatar ?? "")

        return cell

    }

    override func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        let lastElement = datamodel.tableData.count - 1
        let total = datamodel.testfortotal ?? 12
        if indexPath.row == lastElement && datamodel.tableData.count < total{

            datamodel.loadmore(completionHandler: {finish in
                if finish {

                    self.tableView.reloadData()

                }})
        }
    }
}

if using tableView in Your viewController set delegate,datasource self in viewDidLoad.