How to tell when UITableView has completed ReloadData

Question

I am trying to scroll to the bottom of a UITableView after it is done performing  self tableView reloadData   I originally had     self tableView reloadData   NSIndexPath  indexPath    NSIndexPath indexPathForRow    self tableView numberOfRowsInSection   self tableView numberOfSections -1  -1  inSection    self tableView numberOfSections -1      self tableView scrollToRowAtIndexPath indexPath atScrollPosition UITableViewScrollPositionBottom animated YES     But then I read that reloadData is asynchronous  so the scrolling doesn t happen since the self tableView   self tableView numberOfSections  and  self tableView numberOfRowsinSection are all 0   Thanks   What s weird is that I am using    self tableView reloadData   NSLog   Number of Sections  d    self tableView numberOfSections    NSLog   Number of Rows  d    self tableView numberOfRowsInSection   self tableView numberOfSections -1  -1     In the console it returns Sections   1  Row   -1   When I do the exact same NSLogs in cellForRowAtIndexPath I get Sections   1 and Row   8   8 is right

User · Answer

Actually this one solved my problem   - void  tableView  UITableView   tableView willDisplayCell  UITableViewCell   cell forRowAtIndexPath  NSIndexPath   indexPath    NSSet  visibleSections    NSSet setWithArray   tableView indexPathsForVisibleRows  valueForKey   section     if  visibleSections           hide the activityIndicator Loader

User · Answer

The reload happens during the next layout pass  which normally happens when you return control to the run loop  after  say  your button action or whatever returns    So one way to run something after the table view reloads is simply to force the table view to perform layout immediately    self tableView reloadData    self tableView layoutIfNeeded    NSIndexPath  indexPath    NSIndexPath indexPathForRow    self tableView numberOfRowsInSection   self tableView numberOfSections -1  -1  inSection    self tableView numberOfSections -1     self tableView scrollToRowAtIndexPath indexPath atScrollPosition UITableViewScrollPositionBottom animated YES     Another way is to schedule your after-layout code to run later using dispatch async    self tableView reloadData    dispatch async dispatch get main queue            NSIndexPath  indexPath    NSIndexPath indexPathForRow    self tableView numberOfRowsInSection   self tableView numberOfSections -1  -1  inSection   self tableView numberOfSections -1          self tableView scrollToRowAtIndexPath indexPath atScrollPosition UITableViewScrollPositionBottom animated YES         UPDATE  Upon further investigation  I find that the table view sends tableView numberOfSections  and tableView numberOfRowsInSection  to its data source before returning from reloadData   If the delegate implements tableView heightForRowAtIndexPath   the table view also sends that  for each row  before returning from reloadData   However  the table view does not send tableView cellForRowAtIndexPath  or tableView headerViewForSection until the layout phase  which happens by default when you return control to the run loop   I also find that in a tiny test program  the code in your question properly scrolls to the bottom of the table view  without me doing anything special  like sending layoutIfNeeded or using dispatch async

User · Answer

I had the same issues as Tyler Sheaffer   I implemented his solution in Swift and it solved my problems   Swift 3 0   final class UITableViewWithReloadCompletion  UITableView     private var reloadDataCompletionBlock      - gt  Void      override func layoutSubviews         super layoutSubviews        reloadDataCompletionBlock        reloadDataCompletionBlock   nil         func reloadDataWithCompletion completion   escaping    - gt  Void        reloadDataCompletionBlock   completion     self reloadData           Swift 2   class UITableViewWithReloadCompletion  UITableView      var reloadDataCompletionBlock      - gt  Void      override func layoutSubviews         super layoutSubviews        self reloadDataCompletionBlock        self reloadDataCompletionBlock   nil        func reloadDataWithCompletion completion    - gt  Void          reloadDataCompletionBlock   completion       self reloadData           Example Usage   tableView reloadDataWithCompletion         reloadData is guaranteed to have completed

User · Answer

You can use performBatchUpdates function of uitableview  Here is how you can achieve  self tableView performBatchUpdates            Perform reload         self tableView reloadData             completed  in            Reload Completed Use your code here

User · Answer

Try this   tableView backgroundColor    black  tableView reloadData    DispatchQueue main async execute         tableView backgroundColor    green       The tableView color will changed from black to green only after the reloadData   function completes

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I use this trick  pretty sure I already posted it to a duplicate of this question   - void tableViewDidLoadRows  UITableView   tableView         do something after loading  e g  select a cell     -  NSInteger tableView  UITableView   tableView numberOfRowsInSection  NSInteger section          trick to detect when table view has finished loading       NSObject cancelPreviousPerformRequestsWithTarget self selector  selector tableViewDidLoadRows   object tableView        self performSelector  selector tableViewDidLoadRows   withObject tableView afterDelay 0           specific to your controller     return self objects count

User · Answer

Try this way it will work   tblViewTerms performSelectorOnMainThread  selector dataLoadDoneWithLastTermIndex   withObject lastTermIndex waitUntilDone YES  waitUntilDone YES     interface UITableView  TableViewCompletion   - void dataLoadDoneWithLastTermIndex  NSNumber  lastTermIndex    end   implementation UITableView TableViewCompletion   - void dataLoadDoneWithLastTermIndex  NSNumber  lastTermIndex       NSLog   dataLoadDone      NSIndexPath  indexPath    NSIndexPath indexPathForRow   lastTermIndex integerValue  inSection  0     self selectRowAtIndexPath indexPath animated YES scrollPosition UITableViewScrollPositionNone       end   I will execute when table is completely loaded  Other Solution is you can subclass UITableView

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It appears folks are still reading this question and the answers  B c of that  I m editing my answer to remove the word Synchronous which is really irrelevant to this   When  tableView reloadData  returns  the internal data structures behind the tableView have been updated  Therefore  when the method completes you can safely scroll to the bottom  I verified this in my own app  The widely accepted answer by  rob-mayoff  while also confusing in terminology  acknowledges the same in his last update   If your tableView isn t scrolling to the bottom you may have an issue in other code you haven t posted  Perhaps you are changing data after scrolling is complete and you re not reloading and or scrolling to the bottom then   Add some logging as follows to verify that the table data is correct after reloadData  I have the following code in a sample app and it works perfectly      change the data source  NSLog   Before reload   sections    d  last row    d          self tableView numberOfSections          self tableView numberOfRowsInSection  self tableView numberOfSections -1      self tableView reloadData    NSLog   After reload   sections    d  last row    d          self tableView numberOfSections          self tableView numberOfRowsInSection  self tableView numberOfSections -1      self tableView scrollToRowAtIndexPath  NSIndexPath indexPathForRow  self tableView numberOfRowsInSection  self tableView numberOfSections -1 -1                                                           inSection  self tableView numberOfSections  - 1                        atScrollPosition UITableViewScrollPositionBottom                               animated YES

User · Answer

I ended up using a variation of Shawn s solution   Create a custom UITableView class with a delegate   protocol CustomTableViewDelegate       func CustomTableViewDidLayoutSubviews      class CustomTableView  UITableView        var customDelegate  CustomTableViewDelegate       override func layoutSubviews             super layoutSubviews           self customDelegate  CustomTableViewDidLayoutSubviews             Then in my code  I use   class SomeClass  UIViewController  CustomTableViewDelegate         IBOutlet weak var myTableView  CustomTableView       override func viewDidLoad             super viewDidLoad            self myTableView customDelegate   self            func CustomTableViewDidLayoutSubviews             print  didlayoutsubviews              DO other cool things here             Also make sure you set your table view to CustomTableView in the interface builder

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Creating a reusable extension of CATransaction    public extension CATransaction       static func perform method     - gt  Void  completion   escaping    - gt  Void            begin           setCompletionBlock               completion                     method           commit             Now creating an extension of UITableView that would use CATransaction s extension method   public extension UITableView       func reloadData completion   escaping     - gt  Void            CATransaction perform method               reloadData             completion  completion            Usage   tableView reloadData completion          Do the stuff

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Swift      extension UITableView       func reloadData completion  escaping   - gt               UIView animate withDuration  0  animations    self reloadData                      in completion                  somewhere later     tableView reloadData       print  quot done quot      Objective-C   UIView animateWithDuration 0 animations         myTableView reloadData     completion   BOOL finished          Do something after that

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You can use it for do something after reload data    UIView animateWithDuration 0 animations         self contentTableView reloadData     completion   BOOL finished         isUnderwritingUpdate   NO

User · Answer

The dispatch async dispatch get main queue    method above is not guaranteed to work  I m seeing non-deterministic behavior with it  in which sometimes the system has completed the layoutSubviews and the cell rendering before the completion block  and sometimes after   Here s a solution that works 100  for me  on iOS 10   It requires the ability to instantiate the UITableView or UICollectionView as a custom subclass  Here s the UICollectionView solution  but it s exactly the same for UITableView   CustomCollectionView h    import  lt UIKit UIKit h gt    interface CustomCollectionView  UICollectionView  -  void reloadDataWithCompletion  void     void  completionBlock    end   CustomCollectionView m    import  CustomCollectionView h    interface CustomCollectionView      property  nonatomic  copy  void   reloadDataCompletionBlock  void     end   implementation CustomCollectionView  -  void reloadDataWithCompletion  void     void  completionBlock       self reloadDataCompletionBlock   completionBlock       self reloadData      -  void layoutSubviews        super layoutSubviews        if  self reloadDataCompletionBlock            self reloadDataCompletionBlock            self reloadDataCompletionBlock   nil            end   Example usage    self collectionView reloadDataWithCompletion           reloadData is guaranteed to have completed       See here for a Swift version of this answer

User · Answer

In Swift 3 0   we can create a an extension for UITableView with a escaped  Closure like below   extension UITableView       func reloadData completion   escaping    - gt                UIView animate withDuration  0  animations    self reloadData                in completion              And Use it like Below  wherever you want   Your Table View reloadData      print  quot reload done quot       hope this will help to someone  cheers

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Just to offer another approach  based on the idea of the completion being the  last visible  cell to be sent to cellForRow      Will be set when reload is called var lastIndexPathToDisplay  IndexPath   typealias ReloadCompletion     - gt Void  var reloadCompletion  ReloadCompletion   func tableView   tableView  UITableView  cellForRowAt indexPath  IndexPath  - gt  UITableViewCell           Setup cell      if indexPath    self lastIndexPathToDisplay            self lastIndexPathToDisplay   nil          self reloadCompletion            self reloadCompletion   nil               Return cell      func reloadData completion   escaping ReloadCompletion         self reloadCompletion   completion      self mainTable reloadData        self lastIndexPathToDisplay   self mainTable indexPathsForVisibleRows  last       One possible issue is  If reloadData   has finished before the lastIndexPathToDisplay was set  the  last visible  cell will be displayed before lastIndexPathToDisplay was set and the completion will not be called  and will be in  waiting  state    self mainTable reloadData       cellForRowAt could be finished here  before setting  lastIndexPathToDisplay   self lastIndexPathToDisplay   self mainTable indexPathsForVisibleRows  last   If we reverse  we could end up with completion being triggered by scrolling before reloadData     self lastIndexPathToDisplay   self mainTable indexPathsForVisibleRows  last     cellForRowAt could trigger the completion by scrolling here since we arm  lastIndexPathToDisplay  before  reloadData     self mainTable reloadData

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And a UICollectionView version  based on kolaworld s answer   https   stackoverflow com a 43162226 1452758  Needs testing  Works so far on iOS 9 2  Xcode 9 2 beta 2  with scrolling a collectionView to an index  as a closure   extension UICollectionView           Calls reloadsData   on self  and ensures that the given closure is         called after reloadData   has been completed                  Discussion  reloadData   appears to be asynchronous  i e  the         reloading actually happens during the next layout pass  So  doing         things like scrolling the collectionView immediately after a         call to reloadData   can cause trouble                  This method uses CATransaction to schedule the closure       func reloadDataThenPerform   closure   escaping     - gt  Void                        CATransaction begin               CATransaction setCompletionBlock closure              self reloadData           CATransaction commit             Usage   myCollectionView reloadDataThenPerform       myCollectionView scrollToItem at  indexPath              at   centeredVertically              animated  true

User · Answer

Try setting delays     tableView performSelector  selector reloadData  withObject nil afterDelay 0 2     activityIndicator performSelector  selector stopAnimating  withObject nil afterDelay 0 2

User · Answer

As of Xcode 8 2 1  iOS 10  and swift 3    You can determine the end of tableView reloadData   easily by using a CATransaction block   CATransaction begin   CATransaction setCompletionBlock       print  reload completed         Your completion code here    print  reloading   tableView reloadData   CATransaction commit     The above also works for determining the end of UICollectionView s reloadData   and UIPickerView s reloadAllComponents

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Details   Xcode Version 10 2 1  10E1001   Swift 5   Solution  import UIKit     MARK  - UITableView reloading functions  protocol ReloadCompletable  class   func reloadData      extension ReloadCompletable       func run transaction closure      - gt  Void    completion      - gt  Void              guard let closure   closure else   return           CATransaction begin           CATransaction setCompletionBlock completion          closure           CATransaction commit              func run transaction closure      - gt  Void    completion    Self  - gt  Void              run transaction  closure     weak self  in             guard let self   self else   return               completion  self                       func reloadData completion closure    Self  - gt  Void              run transaction     weak self  in self  reloadData      completion  closure              MARK  - UITableView reloading functions  extension ReloadCompletable where Self  UITableView       func reloadRows at indexPaths   IndexPath   with animation  UITableView RowAnimation  completion closure    Self  - gt  Void              run transaction     weak self  in self  reloadRows at  indexPaths  with  animation     completion  closure             func reloadSections   sections  IndexSet  with animation  UITableView RowAnimation  completion closure    Self  - gt  Void              run transaction     weak self  in self  reloadSections sections  with  animation     completion  closure              MARK  - UICollectionView reloading functions  extension ReloadCompletable where Self  UICollectionView        func reloadSections   sections  IndexSet  completion closure    Self  - gt  Void              run transaction     weak self  in self  reloadSections sections     completion  closure             func reloadItems at indexPaths   IndexPath   completion closure    Self  - gt  Void              run transaction     weak self  in self  reloadItems at  indexPaths     completion  closure            Usage     UITableView      Activate extension UITableView  ReloadCompletable                let tableView   UICollectionView       reload data tableView reloadData   tableView in print collectionView        or tableView reloadRows at  indexPathsToReload  with  rowAnimation    tableView in print tableView        or tableView reloadSections IndexSet integer  0   with  rowAnimation     tableView in print tableView         UICollectionView      Activate extension UICollectionView  ReloadCompletable                let collectionView   UICollectionView       reload data collectionView reloadData   collectionView in print collectionView        or collectionView reloadItems at  indexPathsToReload    collectionView in print collectionView        or collectionView reloadSections IndexSet integer  0     collectionView in print collectionView      Full sample     Do not forget to add the solution code here   import UIKit  class ViewController  UIViewController        private weak var navigationBar  UINavigationBar      private weak var tableView  UITableView       override func viewDidLoad             super viewDidLoad           setupNavigationItem           setupTableView              MARK  - Activate UITableView reloadData with completion functions  extension UITableView  ReloadCompletable         MARK  - Setup init  subviews  extension ViewController        private func setupTableView             guard let navigationBar   navigationBar else   return           let tableView   UITableView           view addSubview tableView          tableView translatesAutoresizingMaskIntoConstraints   false         tableView topAnchor constraint equalTo  navigationBar bottomAnchor  isActive   true         tableView leftAnchor constraint equalTo  view leftAnchor  isActive   true         tableView rightAnchor constraint equalTo  view rightAnchor  isActive   true         tableView bottomAnchor constraint equalTo  view bottomAnchor  isActive   true         tableView dataSource   self         self tableView   tableView            private func setupNavigationItem             let navigationBar   UINavigationBar           view addSubview navigationBar          self navigationBar   navigationBar         navigationBar translatesAutoresizingMaskIntoConstraints   false         navigationBar topAnchor constraint equalTo  view safeAreaLayoutGuide topAnchor  isActive   true         navigationBar leftAnchor constraint equalTo  view leftAnchor  isActive   true         navigationBar rightAnchor constraint equalTo  view rightAnchor  isActive   true         let navigationItem   UINavigationItem           navigationItem rightBarButtonItem   UIBarButtonItem title   all   style   plain  target  self  action   selector reloadAllCellsButtonTouchedUpInside source             let buttons   UIBarButtonItem                                                   init title   row   style   plain  target  self                                                    action   selector reloadRowButtonTouchedUpInside source                                                   init title   section   style   plain  target  self                                                    action   selector reloadSectionButtonTouchedUpInside source                                                           navigationItem leftBarButtonItems   buttons         navigationBar items    navigationItem              MARK  - Buttons actions  extension ViewController         objc func reloadAllCellsButtonTouchedUpInside source  UIBarButtonItem            let elementsName    Data          print  -- Reloading   elementsName  started           tableView  reloadData   taleView in             print  -- Reloading   elementsName  stopped   taleView                         private var randomRowAnimation  UITableView RowAnimation           return UITableView RowAnimation rawValue   0   6  randomElement      0     UITableView RowAnimation automatic             objc func reloadRowButtonTouchedUpInside source  UIBarButtonItem            guard let tableView   tableView else   return           let elementsName    Rows          print  -- Reloading   elementsName  started           let indexPathToReload   tableView indexPathsForVisibleRows  randomElement      IndexPath row  0  section  0          tableView reloadRows at   indexPathToReload   with  randomRowAnimation     tableView in               print  --   taleView                print  -- Reloading   elementsName  stopped in    tableView                          objc func reloadSectionButtonTouchedUpInside source  UIBarButtonItem            guard let tableView   tableView else   return           let elementsName    Sections          print  -- Reloading   elementsName  started           tableView reloadSections IndexSet integer  0   with  randomRowAnimation     tableView in               print  --   taleView                print  -- Reloading   elementsName  stopped in    tableView                       extension ViewController  UITableViewDataSource       func numberOfSections in tableView  UITableView  - gt  Int   return 1       func tableView   tableView  UITableView  numberOfRowsInSection section  Int  - gt  Int   return 20       func tableView   tableView  UITableView  cellForRowAt indexPath  IndexPath  - gt  UITableViewCell           let cell   UITableViewCell           cell textLabel  text      Date             return cell           Results

[objective-c] How to tell when UITableView has completed ReloadData?

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