ios UITableView 像 Facebook 应用程序一样滚动到底部时加载更多
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原文地址: http://stackoverflow.com/questions/20269474/
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StackOverFlow
UITableView load more when scrolling to bottom like Facebook application
提问by rokridi
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 data in my list when the user scrolls to the end of the list (like on home page on Facebook application)?
我正在开发一个使用 SQLite 的应用程序。我想使用分页机制显示用户列表（UITableView）。任何人都可以告诉我当用户滚动到列表末尾时如何在我的列表中加载更多数据（例如在 Facebook 应用程序的主页上）？
回答by shinyuX
You can do that by adding a check on where you're at in the cellForRowAtIndexPath:method. This method is easy to understand and to implement :
您可以通过添加检查您在cellForRowAtIndexPath:方法中的位置来做到这一点。这种方法很容易理解和实现：
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
// Classic start method
static NSString *cellIdentifier = @"MyCell";
MyCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (!cell)
{
cell = [[MyCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:MainMenuCellIdentifier];
}
MyData *data = [self.dataArray objectAtIndex:indexPath.row];
// Do your cell customisation
// cell.titleLabel.text = data.title;
BOOL lastItemReached = [data isEqual:[[self.dataArray] lastObject]];
if (!lastItemReached && indexPath.row == [self.dataArray count] - 1)
{
[self launchReload];
}
}
EDIT : added a check on last item to prevent recursion calls. You'll have to implement the method defining whether the last item has been reached or not.
编辑：添加了对最后一项的检查以防止递归调用。您必须实现定义是否已到达最后一项的方法。
EDIT2 : explained lastItemReached
EDIT2 ：解释 lastItemReached
回答by Suragch
Swift
迅速
Method 1: Did scroll to bottom
方法一：滚动到底部
Here is the Swift version of Pedro Rom?o's answer. When the user stops scrolling it checks if it has reached the bottom.
这是Pedro Rom?o 答案的 Swift 版本。当用户停止滚动时，它会检查它是否已到达底部。
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
方法二：到达最后一行
And here is the Swift version of shinyuX's answer. It checks if the user has reached the last row.
这是ShinyuX 答案的 Swift 版本。它检查用户是否已到达最后一行。
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
loadMore()方法示例
I set up these three class variables for fetching batches of data.
我设置了这三个类变量来获取批量数据。
// 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.
这是将更多项目从数据库加载到表视图中的功能。
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
}
}
}
}
回答by Suraj Mirajkar
Better to use willDisplayCellmethod to check if which cell will be loaded.
Once we get the current indexPath.rowis last we can load more cells.
This will load more cells on scrolling down.
最好使用willDisplayCell方法来检查是否将加载哪个单元格。一旦我们获得了最新的电流indexPath.row，我们就可以加载更多的单元格。这将在向下滚动时加载更多单元格。
- (void)tableView:(UITableView *)tableView
willDisplayCell:(UITableViewCell *)cell
forRowAtIndexPath:(NSIndexPath *)indexPath
{
// check if indexPath.row is last row
// Perform operation to load new Cell's.
}
回答by Vasily Bodnarchuk
Details
细节
- Swift 5.1, Xcode 11.2.1
- 斯威夫特 5.1，Xcode 11.2.1
Solution
解决方案
Worked with UIScrollView / UICollectionView / UITableView
使用 UIScrollView / UICollectionView / UITableView
import UIKit
class LoadMoreActivityIndicator {
private let spacingFromLastCell: CGFloat
private let spacingFromLastCellWhenLoadMoreActionStart: CGFloat
private weak var activityIndicatorView: UIActivityIndicatorView?
private weak var scrollView: UIScrollView?
private var defaultY: CGFloat {
guard let height = scrollView?.contentSize.height else { return 0.0 }
return height + spacingFromLastCell
}
deinit { activityIndicatorView?.removeFromSuperview() }
init (scrollView: UIScrollView, spacingFromLastCell: CGFloat, spacingFromLastCellWhenLoadMoreActionStart: CGFloat) {
self.scrollView = scrollView
self.spacingFromLastCell = spacingFromLastCell
self.spacingFromLastCellWhenLoadMoreActionStart = spacingFromLastCellWhenLoadMoreActionStart
let size:CGFloat = 40
let frame = CGRect(x: (scrollView.frame.width-size)/2, y: scrollView.contentSize.height + spacingFromLastCell, width: size, height: size)
let activityIndicatorView = UIActivityIndicatorView(frame: frame)
activityIndicatorView.color = .black
activityIndicatorView.autoresizingMask = [.flexibleLeftMargin, .flexibleRightMargin]
activityIndicatorView.hidesWhenStopped = true
scrollView.addSubview(activityIndicatorView)
self.activityIndicatorView = activityIndicatorView
}
private var isHidden: Bool {
guard let scrollView = scrollView else { return true }
return scrollView.contentSize.height < scrollView.frame.size.height
}
func start(closure: (() -> Void)?) {
guard let scrollView = scrollView, let activityIndicatorView = activityIndicatorView else { return }
let offsetY = scrollView.contentOffset.y
activityIndicatorView.isHidden = isHidden
if !isHidden && offsetY >= 0 {
let contentDelta = scrollView.contentSize.height - scrollView.frame.size.height
let offsetDelta = offsetY - contentDelta
let newY = defaultY-offsetDelta
if newY < scrollView.frame.height {
activityIndicatorView.frame.origin.y = newY
} else {
if activityIndicatorView.frame.origin.y != defaultY {
activityIndicatorView.frame.origin.y = defaultY
}
}
if !activityIndicatorView.isAnimating {
if offsetY > contentDelta && offsetDelta >= spacingFromLastCellWhenLoadMoreActionStart && !activityIndicatorView.isAnimating {
activityIndicatorView.startAnimating()
closure?()
}
}
if scrollView.isDecelerating {
if activityIndicatorView.isAnimating && scrollView.contentInset.bottom == 0 {
UIView.animate(withDuration: 0.3) { [weak self] in
if let bottom = self?.spacingFromLastCellWhenLoadMoreActionStart {
scrollView.contentInset = UIEdgeInsets(top: 0, left: 0, bottom: bottom, right: 0)
}
}
}
}
}
}
func stop(completion: (() -> Void)? = nil) {
guard let scrollView = scrollView , let activityIndicatorView = activityIndicatorView else { return }
let contentDelta = scrollView.contentSize.height - scrollView.frame.size.height
let offsetDelta = scrollView.contentOffset.y - contentDelta
if offsetDelta >= 0 {
UIView.animate(withDuration: 0.3, animations: {
scrollView.contentInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
}) { _ in completion?() }
} else {
scrollView.contentInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
completion?()
}
activityIndicatorView.stopAnimating()
}
}
Usage
用法
init
在里面
activityIndicator = LoadMoreActivityIndicator(scrollView: tableView, spacingFromLastCell: 10, spacingFromLastCellWhenLoadMoreActionStart: 60)
handling
处理
extension ViewController: UITableViewDelegate {
func scrollViewDidScroll(_ scrollView: UIScrollView) {
activityIndicator.start {
DispatchQueue.global(qos: .utility).async {
sleep(3)
DispatchQueue.main.async { [weak self] in
self?.activityIndicator.stop()
}
}
}
}
}
Full Sample
完整样本
Do not forget to paste the solution code.
不要忘记粘贴解决方案代码。
import UIKit
class ViewController: UIViewController {
fileprivate var activityIndicator: LoadMoreActivityIndicator!
override func viewDidLoad() {
super.viewDidLoad()
let tableView = UITableView(frame: view.frame)
view.addSubview(tableView)
tableView.translatesAutoresizingMaskIntoConstraints = false
tableView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
tableView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
tableView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
tableView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
tableView.dataSource = self
tableView.delegate = self
tableView.tableFooterView = UIView()
activityIndicator = LoadMoreActivityIndicator(scrollView: tableView, spacingFromLastCell: 10, spacingFromLastCellWhenLoadMoreActionStart: 60)
}
}
extension ViewController: UITableViewDataSource {
func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 30
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell()
cell.textLabel?.text = "\(indexPath)"
return cell
}
}
extension ViewController: UITableViewDelegate {
func scrollViewDidScroll(_ scrollView: UIScrollView) {
activityIndicator.start {
DispatchQueue.global(qos: .utility).async {
for i in 0..<3 {
print("!!!!!!!!! \(i)")
sleep(1)
}
DispatchQueue.main.async { [weak self] in
self?.activityIndicator.stop()
}
}
}
}
}
Result
结果
回答by samwize
- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
NSInteger lastSectionIndex = [tableView numberOfSections] - 1;
NSInteger lastRowIndex = [tableView numberOfRowsInSection:lastSectionIndex] - 1;
if ((indexPath.section == lastSectionIndex) && (indexPath.row == lastRowIndex)) {
// This is the last cell
[self loadMore];
}
}
If you are using Core Data and NSFetchedResultsController, then loadMorecould look like the following:
如果您使用的是 Core Data 和NSFetchedResultsController，则loadMore可能如下所示：
// Load more
- (void)loadMore {
[self.fetchedResultsController.fetchRequest setFetchLimit:newFetchLimit];
[NSFetchedResultsController deleteCacheWithName:@"cache name"];
NSError *error;
if (![self.fetchedResultsController performFetch:&error]) {
// Update to handle the error appropriately.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
}
[self.tableView reloadData];
}
回答by Pedro Rom?o
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.
我已经实现了我在 stackoverflow 中找到的一个解决方案，它运行良好，但我认为 ShinyuX 的解决方案很容易实现并且适用于我的建议。如果有人想要不同的解决方案，可以使用下面的解决方案。
- (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];
}
}
回答by Retterdesdialogs
Use limit and offset in your queries and fill your tableview with that content. When the user scrolls down, load the next offset.
在您的查询中使用 limit 和 offset 并用该内容填充您的 tableview。当用户向下滚动时，加载下一个偏移量。
Implement the tableView:willDisplayCell:forRowAtIndexPath:method in your UITableViewDelegateand check to see if it's the last row
tableView:willDisplayCell:forRowAtIndexPath:在你的方法中实现UITableViewDelegate并检查它是否是最后一行
回答by Yogi
Below link will provide sample code. #Swift3
下面的链接将提供示例代码。#Swift3
User need to pull up last table view cell, at least hight of 2 cell to fetch more data from server.
用户需要拉起最后一个表格视图单元格，至少 2 个单元格的高度才能从服务器获取更多数据。
You will found Process cell also to show loading process as in last cell.
您还会发现 Process 单元格也显示了最后一个单元格中的加载过程。
Its in Swift3
它在 Swift3 中
回答by Vitalii
One more option to use (Swift 3and iOS 10+):
另一个使用选项（Swift 3和 iOS 10+）：
class DocumentEventsTableViewController: UITableViewController, UITableViewDataSourcePrefetching {
var currentPage: Int = 1
let pageSize: Int = 10 // num of items in one page
override func viewDidLoad() {
super.viewDidLoad()
self.tableView.prefetchDataSource = self
}
func tableView(_ tableView: UITableView, prefetchRowsAt indexPaths: [IndexPath]) {
let upcomingRows = indexPaths.map { extension UITableView{
func indicatorView() -> UIActivityIndicatorView{
var activityIndicatorView = UIActivityIndicatorView()
if self.tableFooterView == nil{
let indicatorFrame = CGRect(x: 0, y: 0, width: self.bounds.width, height: 40)
activityIndicatorView = UIActivityIndicatorView(frame: indicatorFrame)
activityIndicatorView.isHidden = false
activityIndicatorView.autoresizingMask = [.flexibleLeftMargin, .flexibleRightMargin]
activityIndicatorView.isHidden = true
self.tableFooterView = activityIndicatorView
return activityIndicatorView
}else{
return activityIndicatorView
}
}
func addLoading(_ indexPath:IndexPath, closure: @escaping (() -> Void)){
indicatorView().startAnimating()
if let lastVisibleIndexPath = self.indexPathsForVisibleRows?.last {
if indexPath == lastVisibleIndexPath && indexPath.row == self.numberOfRows(inSection: 0) - 1 {
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
closure()
}
}
}
indicatorView().isHidden = false
}
func stopLoading(){
indicatorView().stopAnimating()
indicatorView().isHidden = true
}
}
.row }
if let maxIndex = upcomingRows.max() {
let nextPage: Int = Int(ceil(Double(maxIndex) / Double(pageSize))) + 1
if nextPage > currentPage {
// Your function, which attempts to load respective page from the local database
loadLocalData(page: nextPage)
// Your function, which makes a network request to fetch the respective page of data from the network
startLoadingDataFromNetwork(page: nextPage)
currentPage = nextPage
}
}
}
}
For rather small pages (~ 10 items) you might want to manually add data for pages 1 and 2 because nextPage might be somewhere about 1-2 until the table has a few items to be scrolled well. But it will work great for all next pages.
对于相当小的页面（约 10 个项目），您可能需要手动添加第 1 页和第 2 页的数据，因为 nextPage 可能在大约 1-2 的某个位置，直到表格有几个项目需要滚动。但它适用于所有下一页。
回答by Yogesh Patel
Details
细节
- Swift 5.1, Xcode 11.3.1
- 斯威夫特 5.1，Xcode 11.3.1
Solution
解决方案
Genetic UITableView Extension For Loadmore.
Loadmore 的遗传 UITableView 扩展。
add this UITableView + Extension in your new file
在你的新文件中添加这个 UITableView + Extension
func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
// need to pass your indexpath then it showing your indicator at bottom
tableView.addLoading(indexPath) {
// add your code here
// append Your array and reload your tableview
tableView.stopLoading() // stop your indicator
}
}
Now, just add following line of code in UITableViewDelegate Method willDisplay Cell in your ViewController and make sure tableView.delegate = self
现在，只需在 UITableViewDelegate 方法 willDisplay Cell 在您的 ViewController 中添加以下代码行并确保 tableView.delegate = self
##代码##Result
结果
That's it.. Hope this helpful. Thank You
就是这样..希望这有帮助。谢谢你
