I'm very new to swift programming. I have been playing around with this for a while, but I am not getting anywhere so asking here.
I have a tableview which I can load the data into the view from CoreData no problem. I have an ADD button at the top that segue's to a new tableview, with a long list of options they can pick from. This tableview also works fine, and includes a search bar.
When the user selects an item row from the second tableview, it inserts that item into CoreData and segue's back to the first tableview. This is where my problem is, the data does NOT update on the visible view.
I call tableview.reloaddata() and I can see my code calling the fetchedResultsController with the new query that would return with the new data. But the code never gets to the cellForRowAtIndexPath func so therefore the visible data view never changes. It remains the same display that was visible when the add button was pressed.
How does the visible data get updated? What am I missing?
When using an NSFetchedResultsController, if you want it to "automatically" update the contents of the tableview then there are a couple of things you need to make sure of...
You have to become the NSFetchedResultsControllerDelegate and implements the methods necessary for the updating of the table view. These are quite lengthy and can be found on the Ray Wenderlich website. The code on here is in Objective-C but it's fairly easy to convert to Swift.
The second thing you need is to make sure that the core data update is done on a background thread. Again the website linked above shows this.
Once you've done that then you don't actually need to run [tableview reloadData] because the fetched results controller methods will manage everything for you.
Related
I have a UITableView that contains mutiple sections. When my tab page first loads, everything looks fine. But when I navigate to a different tab, and come back, my UITableView has some extra separator lines.
I verified that numberOfRowsInSection is properly returning 2.
My row height is set to AutomaticDimension.
I am calling reloadData in viewDidAppear.
I tried setting the background color of my table cells to white, but the extra lines are still visible.
The UITableView is inside of a UIScrollView, which I know is frowned upon, but I am doing the calculation to calculate the size of the TableView. Everything works perfectly on initial load, it's not until I return to the tab that I get the extra lines.
In my AccountViewController, I was calling an API to get the user's get account information in ViewDidAppear.
Instead of creating a new TableViewSource, I would clear out the existing data, and the repopulate it with the result of the API call. The flow was something like this.
Clear the Source Data
Call the API
Populate Source with API data
Reload Table Data
I ended up solving the problem by making a call to Reload Table Data after the source was cleared.
Clear the Source Data
Reload Table Data
Call the API
Populate Source with API data
Reload Table Data
Perhaps not the most efficient approach, but it was the easiest to implement within the current structure of the page.
I have multiple data in my UITableView and when I delete one record.
Don't use didEndDisplayingCell to manipulate the cell or the data source array by the passed index path.
It's just a notification that the specified cell was removed from the table
The documentation also states:
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.
The solution is to move the entire code in this method to the location where the cell / data source item is removed and use it before removing anything
The app is crashing because even though you have deleted the object( so now array will have one less element) but you have not told the table view to reset itself according to new datasource. Even cellforRowAt will crash if you delete the last element. One solution is to reload the tableview by calling:
<tableViewName>.reloadData()
but it will produce unnecessary flicker if tableViews are quite large and complex. And the Second thing, You should'nt be using didEndDisplayingCell
I've been searching for a few days, and have continued to learn from reading the apple docs and various tutorials, but there's a problem which I can't seem to get a handle on.
I have a simple app that keeps track of projects, with a single Core Data Entity (ProjectEntry). All the attributes are strings at the moment. It's basically a combination of Paul Hegarty's Core Data lectures and Tim Roadley's web tutorial.
I can add and save Entities and populate a tableview with the data. For the moment, I'm using the CoreDataTableViewController subclass that Hegarty provides in the lecture. I'm mentioning that because...
When my UITableView isn't divided into sections, the new information "instantly" appears in the UI after adding a new entry. However, when I add sections ( via sectionNameKeyPath), the new data still saves, but shows up only after refreshing several times OR waiting 30 seconds before refreshing(via a pull-to-refresh mechanism, which Hegarty also provided).
The tableview delegate methods all seem to be working, as do the NSFetchedResultsController's methods. Using the Stanford/Hegarty CoreDataTableViewController subclass in the past has yielded success, and I've learned a lot reading through the implementation file itself.
The controllers are embedded in a Navigation controller, with the managed object context being passed among the controllers via the prepareForSegue method. Some simple logging shows me the managed object context, initially obtained via a UIManagedDocument, is being successfully passed along.
I've tried the [self.tableview reloadData] and/or the beginUpdates/endUpdates in viewWillAppear, but the delay persists.
What is it about dividing the tableview into sections that's causing the delay? Would calling reloadSections on the tableview be necessary? Like I said, the entries are saved with Core Data and the fetchedResultsController populates the non-sectioned tableview instantly...
It's probably something obvious that I'm just missing, but any help would be appreciated.
Warren Burton's comment above made me re-check if my managed object context behavior was consistent while being passed among the view controllers via the prepareForSegue method.
So, as mentioned in my last comment above, it seems to solve the problem for the moment:
from above:
The initial view controller is non-tableview, which can segue to a UIViewController to add a ProjectEntry, or segue to a UITableViewController which lists saved project entries. This initial view controller creates or uses the UIManagedDocument. By setting a one-line check to see if the UIManagedDoc is being used in this initial view controller's viewWillAppear method, the "delay" in displaying new section data in the tableview seems to stop. I'll test it some more before saying the issue is solved. This way, the shared managed object contexts seem better "bound together" via the managed doc - vapul
I have abit of a problem, I have a coredata object that is used to populate a UITableView. Each UITableViewCell has a couple of buttons that I am using as check boxes, when the user presses one of these text boxes I would like to update coredata and reload the UITableView so all of the arrays I have are updated to reflect the new data.
Thinking about this I have come to the conclusion that its abit redundant or overkill to be reloading the UITableView every time a button is pressed because some of these UITableViews will contain hundreds of rows with two editable UIButtons each.
So I thought that maybe I should update the current array instead then when the view is either exited or the device is put to sleep I could update the coredata object then? the only thing being I don't really know if this is the right thing to do or possible.
The reason this is such a problem is that when I change a button from say a tick to a cross if I scroll away then come back the buttons tick or cross s reverted to its old value.
I would like to know the best way to handle this case as I have never done anything like this before.
You should use an NSFetchedResultsController and its delegate methods to populate the UITableView. Then when the user taps a button, you simply update the corresponding Core Data entity and not the cell. The NSFetchedResultsController will then call its delegate methods, and you can update just that one cell on which the user made a change.
Also, in cellForRowAtIndexPath, you simple fid the corresponding CoreData entity, and use its attributes/properties to adjust the display of the cell.
Remember, that you must always use some data (NSArray usually) from which to read what to do for the cell at the indexPath when the tableView calls cellForRowAtIndexPath:.
This way, when the fetchedResutsController call its delegate methods, you can simply call reloadCellAtIndexPath on the tableView and then the tableView will call cellForRowAtIndexPath again. As the Core Data entity has been updated, your logic for adjusting the display for that cell will cause the cell to look as it should. It's important that you only ever adjust the way a cell looks in cellForRowAtIndexPath, and base the look on a CoreData entity. Change the look of a cell in multiple places, and you will get problems.
A simple tableviewController, empty. A modal that can be launched from a button. No data in the data source for the tableview, and no rows displayed.
I open the modal, use it to add an item, and return to the tableview controller. The tableview updates itself automatically, and the new row is displayed.
I add a second item. The table view does NOT update automatically.
I can tell by logging inside numberOfSectionsInTableView that even if I go to add the first item and cancel, the tableview refreshes - it asks for the number of sections, rows, and the cell to display (if there is one). But not if there is one pre-existing row in the table.
I've scoured my code but can't find anything that would cause the tableview to know when the first item is added, but none afterwards.
Any ideas?
EDIT - I have further narrowed my issue so will close this shortly and have posted a more specific question at Why does an empty tableView check the number of sections but a non-empty one does not?
from Apple's documentation:
UITableView overrides the layoutSubviews method of UIView so that it
calls reloadData only when you create a new instance of UITableView or
when you assign a new data source.
maybe you are setting data source of table view after showing that modal? So at the second time data source does not changes and tableView does not update.
another key (I'm not sure about that) may be the showing of the modal first time. The method -addSubview for modal is causing -layoutSubviews.