My app has two states: logged in and not logged in, and I have the following architecture (vastly simplified):
- ViewController A which contains a search box and a table view.
- ViewController B which is used for logging in the app.
The flow is the following:
- the user is not logged in;
- A is pushed on the stack. In viewWillAppear I check if the user is logged in and if yes, an async network request is being made and, once that is done, the table is loaded with the data from the network. However since the user is not logged in at this point, the table view is empty;
- the user taps on the search box; because he's not logged in, B is pushed (after a confirmation);
- he logs in successfully in B, then presses a button which pops B and shows A again;
- at this point in time, because he's logged in, from viewWillAppear I do the async request;
- when that is completed, I call reloadData on the table view.
What I notice is that numberOfRowsInSection: is called and it returns the correct result, however cellForRowAtIndexPath: is NOT called afterwards and the table remains empty.
I've checked and reloadData is called on the main thread.
Any idea what can it be? Cause it's driving me nuts!
Thanks,
S.
EDIT: Here's the async bit of code from viewWillAppear in A.
if ([User isLoggedIn]) {
[self.asyncRequest fetchDataWithCompletionHandler:^(id response, NSError *error) {
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
if (error) {
[Utils displayError:error];
} else {
self.array = response;
self.isLoaded = YES;
[self.tableView reloadData];
[self.tableView setContentOffset:CGPointMake(0.0f, 0.0f) animated:NO];
}
}];
}
I've checked that the async request completes successfully and that response contains the correct data (this is the array used to back the UITableView).
After reloadData, I've put a breakpoint in tableView:numberOfRowsInSection: and it stops there and it returns the correct number of elements in array. After that, however, the breakpoint in tableView:cellForRowAtIndexPath: is never hit.
One valid scenario for why numberOfRowsInSection would be called but cellForRowAtIndexPath would not be called is when the size or positioning of the table does not require any rows to be displayed.
For example, let's say you had a table that was 20 pixels high, but the header for the first section was 30 high and you returned nil for the header (or did not implement viewForHeaderInSection). In this case, no rows would be displayed and it would look like the table just isn't there.
I see you are using IB. The sizing of the table can be deceptive in IB as it is assuming header and footer sizes. I would log the frame for the table so you understand where it is when the appliction is run (versus where it appears in IB). I would also be sure to manually size and position the table's frame before calling reloadData. This will solve this valid case where cellForRowAtIndexPath is not called.
Check that the numberOfSectionsInTableView is not returning 0.
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return 1;
}
I had the exact same issue and the problem was that I was trying to call reloadData: from another thread. The solution would be:
dispatch_async(dispatch_get_main_queue(), ^{
[self.tableView reloadData];
});
If you are using a different dataSource, as I was, make sure you are retaining the dataSource. Merely instantiating the class that will be the dataSource and assigning it via tableView.dataSource = myDataClass will not be sufficient as the dataSource property of a tableView is weak and will be released when viewDidLoad completes. All of the other methods were being called for me — even, surprisingly, heightForRowAtIndexPath — so this took me some time to debug.
If a Table View inside a view that conflicts something like Scrool View, it does not called. You should separate the views in your Storyboard or *.xib file.
// True
▼ View
► Table View
► Scrool View
► Constraints
// False
▼ View
► Scrool View
► Table View
► Constraints
// For others showing up on this questions via Google, etc.
// Check and make sure you've set the table view's data source and delegate.
self.tableView.dataSource = self;
self.tableView.delegate = self;
We had the same/similar issue. The code reached numberOfSections and numberOfRowsInSection (and it even returned values) but could not reach cellForRowAt. At the time, Table View in the Storyboard had only constraints for right side, left side and top, but not for bottom. Once we added constraint to the bottom, it worked like a charm.
So, check that you provide all needed constraints for the Table View.
If you are using auto layout like me and adding tableview to your view controller's view make sure you have added this line when you are allocating your table view.
tableView?.translatesAutoresizingMaskIntoConstraints = false
Silly mistake from my side.
Everyone keeps talking about height, but my TableView in a StackView with leading alignment ended up with 0 width.
Make sure to check if your TableView is correct size using Debug View Hierarchy.
I solved the problem because my Subview on which i added the UITableView was not allocated so it was returning nill and tableview was not calling cellForRowAtIndexPath but numberOfRowsInSection getting called
Wasted hours and then found out that my tableview was inside a stackview. As soon as I removed the stackview, it worked like a charm. For me it's Xcode 11.3 .
I am using a customer datasource and it was released. Because it is a weak reference of tableview.
This is embarrassing and perplexing, but here's my fix.
My code:
_scanResultTable.delegate = self;
_scanResultTable.dataSource = self; // self's lifecycle was fine, wasn't getting released
[_scanResultTable reloadData];
So the weird part is: the identifier _scanResultTable was never declared in my code, anywhere in the project. I have no idea how this compiled (and I recompiled several times).
My root cause was that I had linked my table output to scanResultTable in my ViewController, but was referring to it as _scanResultTable. Once I started using scanResultTable like I should've been, things cleared up. This makes me wonder if objective-c has something special about leading underscores in identifiers...
Edit: It does! Good lord I can't wait to never touch this language again.
In my case, I had the TableView inside a StackView. When I put it outside the StackView it worked.
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// Make sure self.data isn't nil!
// If it is, you'll always return 0 and therefore
// cellForRowAtIndexPath will never get called.
return [self.data count];
}
I'm using ReactiveCocoa. So I've created the model for table view. The data was prepared to be displayed, so numberOfRows and so on was called. But I haven't added the tableview as subview, thus cellForRowAtIndexPath was not called)))
This maybe too obvious but in my case i was deleting an element (Label) which was a reference to the top margin of my table programmatically, so it was not a problem with delegate/source but of the table having some problems with the content-size / height, this conflict created a weird behaviour, calling numberOfRowsInSection but not cellForRowAt indexPath
Are you sure that after the user logged in and B is popped the viewWillAppear method in A gets called in order to perform the refresh?
If you show B as a modal controller, when you dismiss it you won't have the viewWillAppear method called.
As far as I know, viewWillAppear/viewDidAppear (and other like it) are events generated by the UINavigationController in the case of navigation events (push/pop viewcontrollers).
So maybe that is why you eventually get your refresh when you leave A and return ... it all depends on the way to display the next viewcontroller.
Try to insert new rows manually instead of [self.tableView reloadData]:
[self.tableView beginUpdates];
for (int i = 0; i < responseArray.count; i++) {
_rowsNumber += 1;
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:i inSection:0];
[self.tableView insertRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationBottom];
}
[self.tableView endUpdates];
In dataSource method return incremented int _rowsNumber:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return _rowsNumber;
}
i solved same issue by checking tableViewCell identifier. Go To Attributes İnspector and look at identifier section. Probably is missing. So write cell identifier.
Same case here, but it was a mistake:
I included a Scrollview with 2 tablesViews inside a ViewController (design requirements), in the scrollview controller I created the ViewControllers (that contains the TableViews) programatically and I used a weak var to store it, bad idea because they were released at the end of viewDidLoad method.
If you don't see your tableview content, please, check if it was released.
My mistake was very brain-painful for me because all methods (delegate&datasource) were called except viewForCell...
I have same issue
i have use Table View inside the StackView and table view scroll disable and set height constrain but after that
tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell
Not working stop calling this method all Data Source and Delegate set properly.
if you have same issue than Solution is set Table View bottom , leading , trailing constrain
None of the answers here helped me.
I was using doing my constraints programmatically but forgot to write:
myTableView.translatesAutoresizingMaskIntoConstraints = false
Make sure your constraints are correct and none of them is removed at build time.
Related
When a user adds an item to my list, I want to scroll to the new row, highlight it, and select it (which will push a new controller). The key part is waiting for the scroll animation to complete before pushing the new controller.
In this answer, I learned how to use the animation delegate to wait until the scroll is complete.
However, if the insertion row is already on scree, the table view will not scroll and the method will not fire.
How can I wait to push the new controller until the end of the scroll, and deal with the case where no scroll will be initiated - and how might I tell the difference between each case?
The easiest way to check whether a given row is visible in your table view is something like this:
if (!CGRectContainsRect([self.tableView bounds], [self.tableView rectForRowAtIndexPath:indexPath])
{
// the row is partially outside the table view’s boundaries and needs to be scrolled for full visibility
}
else
{
// the row is within the boundaries and does not need to be scrolled
}
Try creating a method to see if scrolling is needed. If no scrolling is needed, call the push right away, otherwise wait for the delegate call and push.
- (BOOL)isSrollingingNeededForIndexPath:(NSIndexPath *)indexPath {
NSArray *visibleIndices = [self.tableView indexPathsForVisibleRows];
for (NSIndexPath *visibleIndexPath in visibleIndices)
if ([indexPath compare:visibleIndexPath] == NSOrderedSame)
return NO;
return YES;
}
Edit: Good point. Since indexPathsForVisibleRows is used for data rendering.
You could do essentially the same thing with indexPathsForRowsInRect where you use the content.offset.y and the tableview.frame.size.height to determine your "visible rect".
Then to account for partially visible rows at the top and bottom you could add rowHeight-1 to the top of the rect and subtract rowHeight - 1 from the bottom of the rect. Code shouldn't be too gnarly if you have static height rows. If you have varying height rows it would still work, but it would be a bit more involved.
All said though, it seems like a lot of code for something which you'd think would have a simple answer.
I want to add data or cells in UITableview when we scrolled to the last cell of the UITableView. In other words, as we have seen in many iPhone apps, that when we reached to the last cell of the UITableview the more cells get added to it at runtime. I want to achieve that functionality in my project.
Means Add some more cells to the UITableview when we reached to the previously added last cell.
Please tell me the sample code or any tutorial for it.
I think that there are 2 questions here.
First, how to detect the end of tableVeiw? Second, how to add cells dynamically?
First question, I think it can be done by observing the value of content offset of scrollView or current indexPath of tableView cell. The content offset of scrollView can be observed by following method of UIScrollViewDelegate. The content offset is a property of scrollView.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
CGFloat currentOffset = scrollView.contentOffset;
// Detect scrolling to bottom by this offset value.
....
}
The index of cell may be decided by the method of UITableViewDataSource.
- (UITableViewCell *)cellForRowAtIndexPath:(NSIndexPath *)indexPath
Second question can be overwhelmed by the methods of UITableView.
beginUpdates
endUpdates
insertRowsAtIndexPaths:withRowAnimation:
deleteRowsAtIndexPaths:withRowAnimation:
insertSections:withRowAnimation:
deleteSections:withRowAnimation:
I remember the sample codes in this official document will teach how to use above methods. They don't reload all cells, but careless operations will result in crash easily.
If you have data stored in an array, then you would definitely have the count of how many cells you want.
Use the below code for your help
-(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView{ return [array count];}
i believe this would have helped you.
Populate the tableView by using an array (as you should always do). When the delegate method cellForRowAtIndexPath ask your for the last cell, repopulate your array with new (more) data and make a [tableView reloadData].
you just want to add data in table?
Then, first you may need to add one more view, modal view. You should write some specification about what you want to add in this view.
Next you send a message to existing data array(Assume you use array)
[ExistingArrayData addObject:TemporalilyNewObject];
And you can sort the data by using NSSortDescriptor.
NSSortDescriptor *nameSorter = [[NSSortDescriptor alloc] initWithKey:KEY_VALUE ascending:YES selector:#selector(caseInsensitiveCompare:)];
[ExistingArrayData sortUsingDescriptors:[NSArray arrayWithObject:nameSorter]];
In this case, this method sorts the data by KEY_VALUE, ascending.
Finally, you shoule add this code in RootView's viewWillAppear method.
[self.tableView reloadData];
This code notifies app of change of data.
-(void) tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath{
int i=0;
i=indexPath.row;
int count=[urTablearray count];
if (count == (++i)) {
//do ur stuff here
here add object to urTablearray
[urTablearray addObject:#"vijay"];
}
}
Note: urTablearray is NSMutableArray type not NSArray
When I call this Code
[[self tableView]reloadRowsAtIndexPaths:[NSArray arrayWithObject:[NSIndexPath indexPathForRow:0 inSection:kSectionShoppingList]] withRowAnimation:UITableViewRowAnimationNone];
HeightForRowAtIndexPath Calls
But in CellForRowAtIndexPath for section 3 row 0 does not call.
Looking for your suggestion.
and it is specific to Device 3g iOS4.0.1.
Is anyone earlier have faced same issue.
Is the cell you are reloading visible ?
Not sure about iOS4.0.1, don't have it installed to test, but on iOS5+, the cellForRowAtIndexPath is not called if the cell is not visible, just tried it in one of my apps.
The issue i have mentioned look like a bug in iOs4.0.1. anyway I have solved it by reloading whole table using reloadData method instead of reloading particular rows.
Make sure your are reloading sections and rows that are visible and corresponding the the right indices in your tableview. Also check that your tableView delegate and datasource are correctly set.
reloadData method as the following comment :
- (void)reloadData; // reloads everything from scratch. redisplays visible rows. because we only keep info about visible rows, this is cheap. will adjust offset if table shrinks
you may also have trouble reloading single rows if your table is mutating, then you should beginUpdate / endUpdate methods
- (void)beginUpdates; // allow multiple insert/delete of rows and sections to be animated simultaneously. Nestable
- (void)endUpdates; // only call insert/delete/reload calls or change the editing state inside an update block. otherwise things like row count, etc. may be invalid.
I'm trying to insert a bunch of rows into an empty UITableView in one step using insertRowsAtIndexPaths. (I know that this doesn't sound all that useful, but it's a simplified version of what I really need to do.)
The issue I'm seeing is that after I make the insertRowsAtIndexPaths call, I get cellForRowAtIndexPath calls for every row I inserted, rather than just those that are visible.
That doesn't seem right. And it's pretty much useless to me if it does this.
The only slightly odd other artifact I see is that when I do this, it actually seems to animate the rows into place. This isn't the withRowAnimation, since that's set to none. But it seems there's some sort of higher level animation concept going on here. I had the off-idea that as it animated the rows into place it thought it needed cells for more/all the rows until they got pushed off screen. But I can't turn off this animation without just using reloadData which I'd prefer to avoid.
Generally I have a data set that changes behind the scenes. I can carefully go through and construct the changes to generate data for the insert/delete/reload calls. But I can't limit that to what's on screen since then it doesn't match the data provider.
I figure I must be missing something ... any ideas?
(I am doing this within a beginUpdates/endUpdates pair but that seems to make no difference.)
I talked to some Apple folks today. The issue is definitely related to the animation that UITableView does when you insert new rows. This is the animation that happens to create new rows for cells, separate from the animation that is used when those rows are brought in via insertRowsAtIndexPaths.
Since the table-level animation creates new rows through a sort of "grow down" kind of thing, during the insert animation small amounts of many cells are considered visible and the table will call cellForRowAtIndexPath for them.
There doesn't seem to be any alternative implementation for this that works for all cases. The recommended solution for my case is to "lie": figure out what cells will exist on page after the animation and insert those. After that animation completes, insert the remainder of cells that won't show and the table won't call cellForRowAtIndexPath.
This requires implementing an object between the table view and the "real" data source that can "lie" to the table view about the number of rows in the table for the duration of the animation. Painful, but that's apparently what has been done in similar cases.
I had the same problem, what I did was to declare an attribute called bMassiveLoad initialized to false.
Before I do the 'massive load' I set it to true and the first thing I do in the cellForRowAtIndexPath was to check for that attribute.
At the end of the 'maseive load' I set it to false again and call reloadData...
I know that it is not a beautiful answer, but it helps me.
I was able to solve this by combining a few answers from here:
set the massive load boolean as needed as suggested by pocjoc
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
UITableView *tableView = self.tableView;
switch(type) {
case NSFetchedResultsChangeInsert:
massiveLoad = YES;
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
...
}
}
and reload the visible rows when it ends
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
if (massiveLoad) {
massiveLoad = NO;
[self.tableView reloadRowsAtIndexPaths:[self.tableView indexPathsForVisibleRows] withRowAnimation:UITableViewRowAnimationFade];
}
}
UITableView calls the relevant delegate and data source methods immediately after a call to insertRowsAtIndexPaths to get the cells and other content for visible cells. This is regardless of whether or not animated is set to YES or NO.
See the discussion here
If you only want the tableView to update the visible cells, then just update your dataSource and call [tableView reloadData].
I don't know whether the behavior you describe is correct, but UITableView has got two methods: beginUpdates and endUpdates (here) that are meant to optimize redrawing (so that animating is done only at the end, otherwise they are done one by one and this could possibly produce the call to cellForRowAtIndexPath).
Now, I am not sure if this could help you, but perhaps you can give this a try...
I feel like there may be a different way to go about this, but what I have found is that if you have existing cells in the visible range (for example, if you have 10 cells visible at all times and you initialize the tableView with 10 blank cells), when you add new rows, the extra rows are not called in cellForRowAtIndexPath.
So, what to do about it. This is how I went about fixing this. When I created the tableView, I added cells to the visible region. They were blank. Then, when I inserted new rows, I only added index paths for the extra rows (i.e. if I have 10 visible rows and want to add 50 rows, including the visible rows, I only added 40 since the first 10 already exist). This of course leaves you with 10 blank cells. At this point, you can use:
NSArray *indexPaths = [myTableView indexPathsForVisibleCells];
[myTableView reloadRowsAtIndexPaths:indexPaths withRowAnimation:UITableViewRowAnimationNone];
This selects your 10 visible blank cells and reloads them with the new information you have passed in (I assume you load data into an array for this part). You will need to add a little logic to your cellForRowAtIndexPath method such as:
if (![myDataArray count]) {
// create a blank cell;
} else {
// add context to your cells as you want;
}
This should do the trick for you and only load the cells you have showing on the screen
For swift you can try this
self.mainTableView.beginUpdates()
self.mainTableView.insertRowsAtIndexPaths(indexPaths, withRowAnimation: UITableViewRowAnimation.Fade)
self.mainTableView.reloadRowsAtIndexPaths(self.mainTableView.indexPathsForVisibleRows!, withRowAnimation: UITableViewRowAnimation.Fade)
self.mainTableView.endUpdates()
The UITableView will request the visible cells by cellForRowAtIndexPath: method, and it can reduce the processing time when there are many cells, ex 1k cells, and reduce spent memory by reusable cell mechanism. If you need to process all cells, then you should implement a custom method to re-process your source data, and then call [tableView reloadData] to update the UI.
Is there any message I can override called when a Table Cell goes away (on scrolling the table)?
I think it should be something like dealoc.
I'm asking this because I have below situation:
I have a table with many cells (100+) and each of this cell contains a ImageView. For loading the image (from a URL) I'm using NSOperationQueue/NSInvocationOperation. The problem appears when user is scrolling the table before the image is completely loaded: because I'm reusing the cells the image is displayed in wrong cell.
To avoid this I'm thinking to use "cancelAllOperations" of NSOperationQueue object when the cell goes away.
Note: I've tried but is not working if I call this message on "prepareForReuse".
iOS 6:
- (void)tableView:(UITableView *)tableView didEndDisplayingCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
// Cancel operation here for cell at indexPath
}
Why not keeping the images in your table data source - the array that holds all the data for the table?
This way you won't have to load these images once again when scrolling back and it will solve your problem...
You can subclass UITableViewCell (or any UIView) and override willMoveToWindow:. It is called whenever the cell appears (or scrolls off screen).
When it goes out of the window the parameter will be nil:
- (void)willMoveToWindow:(UIWindow *)newWindow
{
[super willMoveToWindow:newWindow];
if (newWindow==nil) {
// Cell is no longer in window
}
}
If there were, it would be in the UITableViewDelegate class reference: http://developer.apple.com/iphone/library/documentation/UIKit/Reference/UITableViewDelegate_Protocol/Reference/Reference.html#//apple_ref/occ/intf/UITableViewDelegate
The only thing they have is willDisplayCell which lets you do last minute adjustments BEFORE the cell appears. They don't have anything for when it disappears, but you could probably figure that out since there are only a certain number of cells on the screen at a time for a given cell height.
So if one is appearing and for a cell height of 80 for instance (in portrait mode so 480px screen height), then you can say that the one 6 cells away is about to disappear (6 cells * 80 pixels = 480). There are a couple other things to consider like which way you are scrolling, but you get the general idea.
Example Code: You should also look at lazy table loading via Apple's sample code http://developer.apple.com/iphone/library/samplecode/LazyTableImages/Introduction/Intro.html
I had the same issue and got some nice feedback in the developer forum. Quinn - The Eskimo from Apple:
As an aside, cancelling a network
small transfer because something has
scrolled off the screen is probably a
performance negative. For small
transfers, it's usually more efficient
to let it run to completion (and cache
the results in case they're needed in
the future). This is because of the
way that NSURLConnection manages HTTP
connection reuse. If you cancel a
transfer, NSURLConnection has to
either a) drop the underlying HTTP
connection on the floor, which means
it can't be reused, or b) continue
reading and just junk the data.
Neither of this is the best use of
resources.
Share and Enjoy
-- Quinn "The Eskimo!"
So, I'm not cancelling all the ImageDownload Operation, but rather only start them, when the user stops scrolling. Up to then only a placeholder is shown:
- (void)scrollViewWillBeginDragging:(UITableView *) tableView
{
self.dragging = TRUE;
}
- (void) scrollViewDidEndDragging: (UITableView *) tableView willDecelerate: (BOOL) decelerate
{
if(!decelerate && self.dragging)
[self loadThumbsForVisibleCells];
else
self.dragging = FALSE;
}
- (void) scrollViewDidEndDecelerating: (UITableView *) tableView
{
[self loadThumbsForVisibleCells];
}
Hope this helps!