I'm trying to use a custom UiCollectionViewLayout but I have a little problem.
In my project I want to load some JSON information and present it in a UICollectionView. I need to load the information from WEB and then (when everything is loaded) I need to reload my Collection View.
If I use the UICollectionViewFlowLayout everything works great. However, when I try to use my own layout, the reloadData doesn't work properly and nothing happens.
I'm reloading the data with an async task:
dispatch_async(dispatch_get_main_queue(), ^{
[self.newsCollectionView reloadData];
});
Thanks
It sounds like you're looking for invalidateLayout, which causes prepareLayout, collectionViewContentSize, layoutAttributesForElementsInRect:etc to be called.
Related
I have a collection view with a flow layout that shows multiple cells. Every cell has some async loading happening before it displays an image and some text. What is the best way to update these cells in succession?
I am doing something like this that works but I'm noticing my collection view gets frozen for a second or so if multiple cells get finished at the same time.
dispatch_async(dispatch_get_main_queue(), ^{
[collectionView reloadItemsAtIndexPaths:#[indexPath]];
});
It would be nice to add some more of your code, But it is actually better to do this kinda stuff with performBatchUpdates instead of doing it in main thread.
- (void)performBatchUpdates:(void (^)(void))updates
completion:(void (^)(BOOL finished))completion;
Here is the documentation
I have this very nice collectionview that loads pictures from my server. Now, if the pictures are loading slowly, the collectionview is actually scrollable, but if the pictures are loading fast, instead, the collectionview is basically frozen until all the cells are finally loaded.
I'm pretty sure this is something related to the fact that I'm using dispatch_async to update the ui (inserting cells and sections), so I'm wondering if there's a way to update the ui that still allows me to scroll the collectionview while the items are being added.
Is there anything I'm missing?
Thanks in advance for your help!
The easiest way to solve this issue is to use SDWebImage an UIImageView alternative , and call the sd_setImageWithURL:placeholderImage: method from the tableView:cellForRowAtIndexPath: UITableViewDataSource method. Everything will be handled for you, from async downloads to caching management.
You can find it here: https://github.com/rs/SDWebImage
So remove any dispatch_async, set right away the number of cells on this method:
- (NSInteger)numberOfItemsInSection:(NSInteger)section;
Scroll performance is going to be good with this tool
I have a UITableView in my application. When the table is scrolled almost to the end, I download more data and reload the table.
If the tableView was scrolling, at the time I call [tableView reloadData]; scrolling stops. How can I achieve effect of not stopping the scroll meanwhile reloadData? I think I need to somehow save scrolling speed and then restore it, but how to do this?
P.D. I really searched this question before asking.
I thing, this method (insertRowsAtIndexPaths:withRowAnimation:) is the key.
There is a use case and a nice tip described on SO: the use case and the tip.
Since UITableView is subclass of UIScrollView, you can use UIScrollViewDelegate's scrollViewWillEndDragging:withVelocity:targetContentOffset:
method to determine how far it is supposed to scroll and then after table reload call setContentOffset:animated: with that target offset (or beginning/ending of tableview if it becomes smaller) to simulate continued scrolling
EDIT: since your targetContentOffset is probably going to be CGRectZero, you will have to recalculate it somehow using velocity from the same method
if i am not wrong you are looking for a function call Lazy load. I can recommend you to search SVPullToRefresh
here!
I have an uicollectionview with supplementaryView for each section.
In each supplementaryView I have some buttons.
In dataSource method collectionView:viewForSupplementaryElementOfKind:atIndexPath: I'm setting the buttons tags with the indexPath.section. I made some delegate methods when a button is pressed and send the section(button.tag) as parameter.
Everything works fine, but here comes the problem:
when I insert or delete a section it must update the buttons tags, but I don't want to reload all the items from each section.
I've tried:
to get the supplementaryViews with the dataSource method collectionView:viewForSupplementaryElementOfKind:atIndexPath: and call layoutIfNeeded method for each supplementaryView, in this way the supplementaryViews are reloading, but this approach multiply my supplementaryViews.
a fast for in collectionView.subviews and get just the supplementaryView and call layoutIfNeeded method, but it doesn't reload, just the layout is reloading.
reloadSections: method, but this reload all items from the section
Ohh.. And I use NSFetchedResultsController(delegate) for inserting and deleting sections.
Can anyone help me with this? Is there a way to reload only the supplementaryView? Is there other approach for this scenario?
Thank You!
To reload supplementary views you can use -invalidateLayoutWithContext:.
See documentation for UICollectionViewLayoutInvalidationContext and method -invalidateSupplementaryElementsOfKind:atIndexPaths: (available since iOS 8).
Instead of reloading these views, getting a reference to each visible supplementary view so that you can change the tag might be sufficient for your needs.
There is a simple method you can use to do this:
let supplementaryViews = collectionView.visibleSupplementaryViews(ofKind: "identifier")
https://developer.apple.com/documentation/uikit/uicollectionview/1618026-visiblesupplementaryviews
I'm using a UITableView which loads data from a server. I need to use async ASIHTTPRequest, which is in a separate .m.
How could I force to reload the table data when the requestFinished:request is called?
Thanks!
You can just send the data that needs to be loaded into the TableView by passing it between files. and then finally call a different method of inside the table view that implements the command [self.tableview relaodData];
Update:
What i see from your comments is that the you have a tableView CONtroller or someform of controller that loads the data by calling another class that holds the ASIHTTPrequest/ ansynchrinous requsts. now You have also told me that the TableView Also hold a UIViewController in each cell which i Dont think is a good idea you could go with a custom cell method have a look at this 4 part tutorial... now and the data that needs to be loaded into the TableView is loaded by TableViewController by some method wither it be each cell or something... so after you are able to get the data just inside the tableViewController just Call the [self.tablebview reloadData] inside the TableViewController which is the parent of the TableView there is no need to call in the other methods.
Finally solved with observers although when the app is completely closed won't work. I'll think in something.
Thanks