How to use UIColliectionView's collectionView:didDeselectItemAtIndexPath method asynchronously - ios

In UICollectionView when i select a cell, it opens a new UIViewController where some info is displayed.
- (void)collectionView:(UICollectionView *)collectionView
didDeselectItemAtIndexPath:(NSIndexPath *)indexPath
{
MyClass *myClass = [myClassArray objectAtIndex:indexPath.item];
[myClass MyClassInstanceMethod];
}
In new UIViewController some info about myClass instance is printed. However, in MyClassInstanceMethod i make some HTTP requests which get some data and assign to myClass's properties. As you may guess, the problem is HTTP requests delay and i am not able to get data to be assigned before new view get load.
Then i think that i should let my UICollectionView to open selected cell's page after MyClassInstanceMethod finishes it job. How can i implement that? Thanks in advance.

As my understanding,
you have to make http call in
- (void)collectionView:(UICollectionView *)collectionView
didDeselectItemAtIndexPath:(NSIndexPath *)indexPath;
and in success response you should open your UIViewController with Details you want to show in it.

To keep your method encapsulated by the class, you should put a completion handler in your MyClassInstanceMethod. Like
- (void)MyClassInstanceMethodWithCompletion:(void (^)(BOOL finished))completion {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// Do your HTTP Requests here
dispatch_async(dispatch_get_main_queue(), ^{ // This will be called just when the http requests finish
if (completion) { // Here you could check it out if the requests went well
completion(YES); // If YES return YES
}
});
});
}
Inside of the didDeselectItemAtIndexPath: you can call this like:
- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath {
MyClass *myClass = [myClassArray objectAtIndex:indexPath.item];
[myClass MyClassInstanceMethodWithCompletion:^(BOOL finished) {
if(finished){
// Call the segue
}
}];
}
I hope this can help.
ps: you have used a method name starting with uppercase MyClass... usually it's better a lowercase myClass... it's a better approach just to differentiate a Class name of a Method name.

Related

How do I delay execution of a delegate method of one protocol until the delegate method of another protocol has completed execution?

In the .m file ClassroomCollectionViewController, I have the following instance variable declared:
#implementation ClassroomCollectionViewController
{
NSMutableArray *students;
}
This array is populated in the following delegate method of the NSURLConnectionDataDelegate protocol, which ClassroomCollectionViewController implements.
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
if (connection == _getStudentsEnrolledInClassConnection)
{
// Parse the JSON that came in
NSError *error;
NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData:_receivedData options:NSJSONReadingAllowFragments error:&error];
if (jsonArray.count > 0)
{
students = [[NSMutableArray alloc] init];
// Populate the students array
for (int i = 0; i < jsonArray.count; i++)
{
Student *studentInClass = [Student new];
studentInClass.name = jsonArray[i][#"name"];
studentInClass.profile = jsonArray[i][#"profile"];
studentInClass.profileImageName = jsonArray[i][#"profile_image_name"];
[students addObject:studentInClass];
}
}
}
}
In the following delegate method of another protocol, namely the UICollectionViewDelegate, the students array populated above is used to construct the individual cells of the collection view.
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
ClassmateCollectionViewCell *myCell = [collectionView
dequeueReusableCellWithReuseIdentifier:#"ClassmateCell"
forIndexPath:indexPath];
UIImage *image;
long row = [indexPath row];
image = [UIImage imageNamed:[students[row] profileImageName]];
myCell.imageView.image = image;
myCell.classmateNameLabel.text = [students[row] name];
return myCell;
}
The problem is that the students array is not yet populated by the time that the second of the two delegate methods above executes, which results in there being no data for the cells in the collection view to display.
The obvious solution to this problem is to delay the execution of the second method until the first one has finished executing (thus ensuring that the students array will be populated by the time the cells in the collection view are constructed). But I couldn't for the life of me figure out how to make this so in this particular context - since I have no control over when the second delegate method is invoked. I have considered using blocks and multithreading in order to solve this, but have failed at coming up with a solution that is relevant for this specific problem.
Could anyone point me in the right direction?
Thanks very much,
Jay
Try this, connect an IBOutlet to collection view and
in your connectionDidFinishLoading: method
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
//All other codes for populating `students` array
[self.collectionView reloadData];
}
To delay execution of the collection view, you need to wait until the connectionDidFinishLoading calls.
Its pretty simple you can reload collection view from connectionDidFinishLoading method.
Thats it.
This is design problem. It suppose to go like this (MVC patern):
some service is receiving data by NSURLConnectionDataDelegate sends results to model.
model enforces main thread, updates its data and posts some notification
view controller is registered for model notification and properly reacts on those notifications. Like [self.collectionView reloadData]; or [self.collectionView insertItemsAtIndexPaths: indexPaths]; and so on.

Reload collection view with new data IOS7

Hi I am developing small IOS application and I am new to IOS development. In my application I am using collection view to display my data. What i am doing I am fetching data from my server and then displaying in my UIView controller. Here is my code looks like
- (void)viewDidLoad
{
[super viewDidLoad];
// call for fetching data from server
}
// My collection view methods
-(NSInteger) numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
return 1;
}
-(NSInteger) collectionView:(UICollectionView *)collectionView numberOfItemsInSection: (NSInteger)section
{
return [_channelArray count];
}
-(UICollectionViewCell *) collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"Cell" forIndexPath:indexPath];
cell.image = // set image from channel array.
return cell;
}
// callback for m web service call
-(void) didReceiveSubscriberChannelList:(SubscriberChannelListDataModel *)subscriberChannelListInfo
{
_channelList = subscriberChannelListInfo;
_channelArray = subscriberChannelListInfo.chanellist;
[collectionView reloadData];
}
Above code works with static data. But now I want to display my server data. My reload data not working. How to do this. Need Help. Thank you.
Did you consider put the callback method data in a block?
// callback for m web service call
-(void) didReceiveSubscriberChannelList:(SubscriberChannelListDataModel *)subscriberChannelListInfo
{
dispatch_async(dispatch_get_main_queue(), ^{
_channelList = subscriberChannelListInfo;
_channelArray = subscriberChannelListInfo.chanellist;
[collectionView reloadData];
});
}
This way, when the callback returns it will reload the data in the main thread (the UI thread)

Issue reloading cellForRowAtIndexPath calling from a method in another class - Objective C

I have the following method within a ViewController class:
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:
(NSIndexPath *)indexPath
{
UITableViewCell *cell = [collectionView cellForItemAtIndexPath:indexPath];
NSInteger tag = cell.tag;
// SEND TO SINGLE NEWS FEED TO DISPLAY THE INFORMATION OF THE VIDEO
singleNewsFeed* myScript = [[singleNewsFeed alloc] init];
[myScript startProcess:tag];
[self performSegueWithIdentifier:#"moveToSingleData" sender:self];
}
The receiver class:
- (void)startProcess:(NSInteger)number {
NSInteger check = number;
singlecellID = check;
// MAKE REQuEST TO SERVER
[self makeRequests];
dispatch_async(dispatch_get_main_queue(), ^{
[self.tableView reloadData];
});
}
So what happens is that makeRequests runs and the tableView is refreshed. All methods for the tableView run except the cellForRowAtIndexPath
Here is the thing I know that all of these work properly because I have the same exact classes doing the same exact thing except they are sub viewcontrollers of a parent viewcontroller. I had the same exact issue and used self.parentViewController.childViewControllers[1]; to fix that when calling the method and it worked perfect. But this is different because this is a completely separate ViewController. So therefore I am not sure what to use to call that ViewController that allows cellForRowAtIndexPath to work correctly.
Suggestions, thoughts?
David
You're calling [self.tableView reloadData] but I don't think object you're calling it from is your table view controller. No?

Cancel NSTimers associated with UITableViewCells when they go offscreen

I implement a UITableView of UIImageView cells, each of which periodically refreshes itself every 5 seconds via NSTimer. Each image is loaded from a server in the background thread, and from that background thread I also update the UI, displaying the new image, by calling performSelectorOnMainThread. So far so good.
The problem I noticed is the number of threads is increasing over time and UI becomes non-responsive. Therefore, I want to invalidate NSTimer if a cell goes off screen. Which delegation methods in UITableView should I use to do this efficiently?
The reason why I associate an NSTimer with each cell because I don't want image transition to occur at the same time for all cells.
Is there any other methods to do this by the way? For example, is it possible to use just a single NSTimer?
(I can't use SDWebImage because my requirement is to display a set of images in loop loaded from a server)
// In MyViewController.m
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
...
NSTimer* timer=[NSTimer scheduledTimerWithTimeInterval:ANIMATION_SCHEDULED_AT_TIME_INTERVAL
target:self
selector:#selector(updateImageInBackground:)
userInfo:cell.imageView
repeats:YES];
...
}
- (void) updateImageInBackground:(NSTimer*)aTimer
{
[self performSelectorInBackground:#selector(updateImage:)
withObject:[aTimer userInfo]];
}
- (void) updateImage:(AnimatedImageView*)animatedImageView
{
#autoreleasepool {
[animatedImageView refresh];
}
}
// In AnimatedImageView.m
-(void)refresh
{
if(self.currentIndex>=self.urls.count)
self.currentIndex=0;
ASIHTTPRequest *request=[[ASIHTTPRequest alloc] initWithURL:[self.urls objectAtIndex:self.currentIndex]];
[request startSynchronous];
UIImage *image = [UIImage imageWithData:[request responseData]];
// How do I cancel this operation if I know that a user performs a scrolling action, therefore departing from this cell.
[self performSelectorOnMainThread:#selector(performTransition:)
withObject:image
waitUntilDone:YES];
}
-(void)performTransition:(UIImage*)anImage
{
[UIView transitionWithView:self duration:1.0 options:(UIViewAnimationOptionTransitionCrossDissolve | UIViewAnimationOptionAllowUserInteraction) animations:^{
self.image=anImage;
currentIndex++;
} completion:^(BOOL finished) {
}];
}
willMoveToSuperview: and/or didMoveToSuperview: do not work on ios 6.0
from ios 6.0 you have the following method of UITableViewDelegate
- (void)tableView:(UITableView *)tableView didEndDisplayingCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
Use this method to detect when a cell is removed from a table view, as
opposed to monitoring the view itself to see when it appears or
disappears.
If you properly manage memory and dequeue reusable cells, you can subclass UITableViewCell and override its - prepareForReuse method in order to stop the timer.
Furthermore, as #lnfaziger points out, if you want to stop the timer immediately when the cell is removed from the table view, you can also override its willMoveToSuperview: and/or didMoveToSuperview: method and check if its superview parameter is nil - if it is, the cell is being removed, so you can stop the timer.

Get notified when UITableView has finished asking for data?

Is there some way to find out when a UITableView has finished asking for data from its data source?
None of the viewDidLoad/viewWillAppear/viewDidAppear methods of the associated view controller (UITableViewController) are of use here, as they all fire too early. None of them (entirely understandably) guarantee that queries to the data source have finished for the time being (eg, until the view is scrolled).
One workaround I have found is to call reloadData in viewDidAppear, since, when reloadData returns, the table view is guaranteed to have finished querying the data source as much as it needs to for the time being.
However, this seems rather nasty, as I assume it is causing the data source to be asked for the same information twice (once automatically, and once because of the reloadData call) when it is first loaded.
The reason I want to do this at all is that I want to preserve the scroll position of the UITableView - but right down to the pixel level, not just to the nearest row.
When restoring the scroll position (using scrollRectToVisible:animated:), I need the table view to already have sufficient data in it, or else the scrollRectToVisible:animated: method call does nothing (which is what happens if you place the call on its own in any of viewDidLoad, viewWillAppear or viewDidAppear).
This answer doesn't seem to be working anymore, due to some changes made to UITableView implementation since the answer was written. See this comment : Get notified when UITableView has finished asking for data?
I've been playing with this problem for a couple of days and think that subclassing UITableView's reloadData is the best approach :
- (void)reloadData {
NSLog(#"BEGIN reloadData");
[super reloadData];
NSLog(#"END reloadData");
}
reloadData doesn't end before the table has finish reload its data. So, when the second NSLog is fired, the table view has actually finish asking for data.
I've subclassed UITableView to send methods to the delegate before and after reloadData. It works like a charm.
I did have a same scenario in my app and thought would post my answer to you guys as other answers mentioned here does not work for me for iOS7 and later
Finally this is the only thing that worked out for me.
[yourTableview reloadData];
dispatch_async(dispatch_get_main_queue(),^{
NSIndexPath *path = [NSIndexPath indexPathForRow:yourRow inSection:yourSection];
//Basically maintain your logic to get the indexpath
[yourTableview scrollToRowAtIndexPath:path atScrollPosition:UITableViewScrollPositionTop animated:YES];
});
Swift Update:
yourTableview.reloadData()
dispatch_async(dispatch_get_main_queue(), { () -> Void in
let path : NSIndexPath = NSIndexPath(forRow: myRowValue, inSection: mySectionValue)
//Basically maintain your logic to get the indexpath
yourTableview.scrollToRowAtIndexPath(path, atScrollPosition: UITableViewScrollPosition.Top, animated: true)
})
So how this works.
Basically when you do a reload the main thread becomes busy so at that time when we do a dispatch async thread, the block will wait till the main thread gets finished. So once the tableview has been loaded completely the main thread will gets finish and so it will dispatch our method block
Tested in iOS7 and iOS8 and it works awesome;)
Update for iOS9: This just works fine is iOS9 also. I have created a sample project in github as a POC.
https://github.com/ipraba/TableReloadingNotifier
I am attaching the screenshot of my test here.
Tested Environment: iOS9 iPhone6 simulator from Xcode7
EDIT: This answer is actually not a solution. It probably appears to work at first because reloading can happen pretty fast, but in fact the completion block doesn't necessarily get called after the data has fully finished reloading - because reloadData doesn't block. You should probably search for a better solution.
To expand on #Eric MORAND's answer, lets put a completion block in. Who doesn't love a block?
#interface DUTableView : UITableView
- (void) reloadDataWithCompletion:( void (^) (void) )completionBlock;
#end
and...
#import "DUTableView.h"
#implementation DUTableView
- (void) reloadDataWithCompletion:( void (^) (void) )completionBlock {
[super reloadData];
if(completionBlock) {
completionBlock();
}
}
#end
Usage:
[self.tableView reloadDataWithCompletion:^{
//do your stuff here
}];
reloadData just asking for data for the visible cells. Says, to be notified when specify portion of your table is loaded, please hook the tableView: willDisplayCell: method.
- (void) reloadDisplayData
{
isLoading = YES;
NSLog(#"Reload display with last index %d", lastIndex);
[_tableView reloadData];
if(lastIndex <= 0){
isLoading = YES;
//Notify completed
}
- (void) tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
if(indexPath.row >= lastIndex){
isLoading = NO;
//Notify completed
}
That is my solution. 100% works and used in many projects. It's a simple UITableView subclass.
#protocol MyTableViewDelegate<NSObject, UITableViewDelegate>
#optional
- (void)tableViewWillReloadData:(UITableView *)tableView;
- (void)tableViewDidReloadData:(UITableView *)tableView;
#end
#interface MyTableView : UITableView {
struct {
unsigned int delegateWillReloadData:1;
unsigned int delegateDidReloadData:1;
unsigned int reloading:1;
} _flags;
}
#end
#implementation MyTableView
- (id<MyTableViewDelegate>)delegate {
return (id<MyTableViewDelegate>)[super delegate];
}
- (void)setDelegate:(id<MyTableViewDelegate>)delegate {
[super setDelegate:delegate];
_flags.delegateWillReloadData = [delegate respondsToSelector:#selector(tableViewWillReloadData:)];
_flags.delegateDidReloadData = [delegate respondsToSelector:#selector(tableViewDidReloadData:)];
}
- (void)reloadData {
[super reloadData];
if (_flags.reloading == NO) {
_flags.reloading = YES;
if (_flags.delegateWillReloadData) {
[(id<MyTableViewDelegate>)self.delegate tableViewWillReloadData:self];
}
[self performSelector:#selector(finishReload) withObject:nil afterDelay:0.0f];
}
}
- (void)finishReload {
_flags.reloading = NO;
if (_flags.delegateDidReloadData) {
[(id<MyTableViewDelegate>)self.delegate tableViewDidReloadData:self];
}
}
#end
It's similar to Josh Brown's solution with one exception. No delay is needed in performSelector method. No matter how long reloadData takes. tableViewDidLoadData: always fires when tableView finishes asking dataSource cellForRowAtIndexPath.
Even if you do not want to subclass UITableView you can simply call [performSelector:#selector(finishReload) withObject:nil afterDelay:0.0f] and your selector will be called right after the table finishes reloading. But you should ensure that selector is called only once per call to reloadData:
[self.tableView reloadData];
[self performSelector:#selector(finishReload) withObject:nil afterDelay:0.0f];
Enjoy. :)
This is an answer to a slightly different question: I needed to know when UITableView had also finished calling cellForRowAtIndexPath(). I subclassed layoutSubviews() (thanks #Eric MORAND) and added a delegate callback:
SDTableView.h:
#protocol SDTableViewDelegate <NSObject, UITableViewDelegate>
#required
- (void)willReloadData;
- (void)didReloadData;
- (void)willLayoutSubviews;
- (void)didLayoutSubviews;
#end
#interface SDTableView : UITableView
#property(nonatomic,assign) id <SDTableViewDelegate> delegate;
#end;
SDTableView.m:
#import "SDTableView.h"
#implementation SDTableView
#dynamic delegate;
- (void) reloadData {
[self.delegate willReloadData];
[super reloadData];
[self.delegate didReloadData];
}
- (void) layoutSubviews {
[self.delegate willLayoutSubviews];
[super layoutSubviews];
[self.delegate didLayoutSubviews];
}
#end
Usage:
MyTableViewController.h:
#import "SDTableView.h"
#interface MyTableViewController : UITableViewController <SDTableViewDelegate>
#property (nonatomic) BOOL reloadInProgress;
MyTableViewController.m:
#import "MyTableViewController.h"
#implementation MyTableViewController
#synthesize reloadInProgress;
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
if ( ! reloadInProgress) {
NSLog(#"---- numberOfSectionsInTableView(): reloadInProgress=TRUE");
reloadInProgress = TRUE;
}
return 1;
}
- (void)willReloadData {}
- (void)didReloadData {}
- (void)willLayoutSubviews {}
- (void)didLayoutSubviews {
if (reloadInProgress) {
NSLog(#"---- layoutSubviewsEnd(): reloadInProgress=FALSE");
reloadInProgress = FALSE;
}
}
NOTES:
Since this is a subclass of UITableView which already has a delegate property pointing to MyTableViewController there's no need to add another one. The "#dynamic delegate" tells the compiler to use this property. (Here's a link describing this: http://farhadnoorzay.com/2012/01/20/objective-c-how-to-add-delegate-methods-in-a-subclass/)
The UITableView property in MyTableViewController must be changed to use the new SDTableView class. This is done in the Interface Builder Identity Inspector. Select the UITableView inside of the UITableViewController and set its "Custom Class" to SDTableView.
I had found something similar to get notification for change in contentSize of TableView. I think that should work here as well since contentSize also changes with loading data.
Try this:
In viewDidLoad write,
[self.tableView addObserver:self forKeyPath:#"contentSize" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld | NSKeyValueObservingOptionPrior context:NULL];
and add this method to your viewController:
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
if ([keyPath isEqualToString:#"contentSize"]) {
DLog(#"change = %#", change.description)
NSValue *new = [change valueForKey:#"new"];
NSValue *old = [change valueForKey:#"old"];
if (new && old) {
if (![old isEqualToValue:new]) {
// do your stuff
}
}
}
}
You might need slight modifications in the check for change. This had worked for me though.
Cheers! :)
Here's a possible solution, though it's a hack:
[self.tableView reloadData];
[self performSelector:#selector(scrollTableView) withObject:nil afterDelay:0.3];
Where your -scrollTableView method scrolls the table view with -scrollRectToVisible:animated:. And, of course, you could configure the delay in the code above from 0.3 to whatever seems to work for you. Yeah, it's ridiculously hacky, but it works for me on my iPhone 5 and 4S...
I had something similar I believe. I added a BOOL as instance variable which tells me if the offset has been restored and check that in -viewWillAppear:. When it has not been restored, I restore it in that method and set the BOOL to indicate that I did recover the offset.
It's kind of a hack and it probably can be done better, but this works for me at the moment.
It sounds like you want to update cell content, but without the sudden jumps that can accompany cell insertions and deletions.
There are several articles on doing that. This is one.
I suggest using setContentOffset:animated: instead of scrollRectToVisible:animated: for pixel-perfect settings of a scroll view.
You can try the following logic:
-(UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"MyIdentifier"];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:#"MyIdentifier"];
cell.selectionStyle = UITableViewCellSelectionStyleNone;
}
if ( [self chkIfLastCellIndexToCreate:tableView :indexPath]){
NSLog(#"Created Last Cell. IndexPath = %#", indexPath);
//[self.activityIndicator hide];
//Do the task for TableView Loading Finished
}
prevIndexPath = indexPath;
return cell;
}
-(BOOL) chkIfLastCellIndexToCreate:(UITableView*)tableView : (NSIndexPath *)indexPath{
BOOL bRetVal = NO;
NSArray *visibleIndices = [tableView indexPathsForVisibleRows];
if (!visibleIndices || ![visibleIndices count])
bRetVal = YES;
NSIndexPath *firstVisibleIP = [visibleIndices objectAtIndex:0];
NSIndexPath *lastVisibleIP = [visibleIndices objectAtIndex:[visibleIndices count]-1];
if ((indexPath.row > prevIndexPath.row) && (indexPath.section >= prevIndexPath.section)){
//Ascending - scrolling up
if ([indexPath isEqual:lastVisibleIP]) {
bRetVal = YES;
//NSLog(#"Last Loading Cell :: %#", indexPath);
}
} else if ((indexPath.row < prevIndexPath.row) && (indexPath.section <= prevIndexPath.section)) {
//Descending - scrolling down
if ([indexPath isEqual:firstVisibleIP]) {
bRetVal = YES;
//NSLog(#"Last Loading Cell :: %#", indexPath);
}
}
return bRetVal;
}
And before you call reloadData, set prevIndexPath to nil. Like:
prevIndexPath = nil;
[mainTableView reloadData];
I tested with NSLogs, and this logic seems ok. You may customise/improve as needed.
finally i have made my code work with this -
[tableView scrollToRowAtIndexPath:scrollToIndex atScrollPosition:UITableViewScrollPositionTop animated:YES];
there were few things which needed to be taken care of -
call it within "- (UITableViewCell *)MyTableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath"
just ensure that "scrollToRowAtIndexPath" message is sent to relevant instance of UITableView, which is definitely MyTableview in this case.
In my case UIView is the view which contains instance of UITableView
Also, this will be called for every cell load. Therefore, put up a logic inside "cellForRowAtIndexPath" to avoid calling "scrollToRowAtIndexPath" more than once.
You can resize your tableview or set it content size in this method when all data loaded:
- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
tableView.frame =CGRectMake(tableView.frame.origin.x, tableView.frame.origin.y, tableView.frame.size.width, tableView.contentSize.height);
}
I just run repeating scheduled timer and invalidate it only when table's contentSize is bigger when tableHeaderView height (means there is rows content in the table). The code in C# (monotouch), but I hope the idea is clear:
public override void ReloadTableData()
{
base.ReloadTableData();
// don't do anything if there is no data
if (ItemsSource != null && ItemsSource.Length > 0)
{
_timer = NSTimer.CreateRepeatingScheduledTimer(TimeSpan.MinValue,
new NSAction(() =>
{
// make sure that table has header view and content size is big enought
if (TableView.TableHeaderView != null &&
TableView.ContentSize.Height >
TableView.TableHeaderView.Frame.Height)
{
TableView.SetContentOffset(
new PointF(0, TableView.TableHeaderView.Frame.Height), false);
_timer.Invalidate();
_timer = null;
}
}));
}
}
Isn't UITableView layoutSubviews called just before the table view displays it content? I've noticed that it is called once the table view has finished load its data, maybe you should investigate in that direction.
Since iOS 6 onwards, the UITableview delegate method called:
-(void)tableView:(UITableView *)tableView willDisplayHeaderView:(UIView *)view forSection:(NSInteger)section
will execute once your table reloads successfully. You can do customisation as required in this method.
The best solution I've found in Swift
extension UITableView {
func reloadData(completion: ()->()) {
self.reloadData()
dispatch_async(dispatch_get_main_queue()) {
completion()
}
}
}
Why no just extend?
#interface UITableView(reloadComplete)
- (void) reloadDataWithCompletion:( void (^) (void) )completionBlock;
#end
#implementation UITableView(reloadComplete)
- (void) reloadDataWithCompletion:( void (^) (void) )completionBlock {
[self reloadData];
if(completionBlock) {
completionBlock();
}
}
#end
scroll to the end:
[self.table reloadDataWithCompletion:^{
NSInteger numberOfRows = [self.table numberOfRowsInSection:0];
if (numberOfRows > 0)
{
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:numberOfRows-1 inSection:0];
[self.table scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionTop animated:NO];
}
}];
Not tested with a lot of data

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