I have an NSManagedObject-subclass Event - with some event data in user's life, also it have an NSNumber-type field called time, with unix timestamp representation of when this event had place. So typically user will have many Events. In showing current Event data through tableView I also need to show some data from previous by date Event. Does Core Data have some marks when objects created, that I can directly know what exactly Event was created before current, or do I need to fetch with predicate by value of time?
You should fetch objects from CoreData, and if you're using UITableView it's a good practice to use NSFetchedResultsController, which has a lot of good features for presentation data in UITableView
Related
I'm trying to use Apple's sample project with expand/collapse UITableView sections https://developer.apple.com/Library/ios/samplecode/TableViewUpdates/Introduction/Intro.html
The problem is that I'm trying to use it with CoreData NSFetchedResultsController, and I don't know how to change Apple's code to work with it.
The simple, if not very pleasant, answer is to store the expanded / collapsed status into the Core Data store and then use a predicate with the FRC request so you can change the store contents and it will automatically update the table.
Alternative could be to mutate the data you get from the FRC when the table view requests info from the delegate, which is also messy.
Depending on your data you could use multiple FRCs, one for each section, though this may not be very extensible.
I am badly struck in a issue where I am trying to populate the nestableview lazily. Below is my approach.
I have created a custom class PRIList where it has an instance of array to manage the models.
I have bound the priList.items to the array controller in the xib where items is not an instance in PRIList but to support lazy loading I have implemented the methods countOfItems and objectInItemsAtIndex:.
Initialy when I populate the PRIList I populate few objects (say 50) with valid objects and rest with the faulty objects. In the objectInItemsAtIndex I check if the item at particular index is valid or faulty. If it is faulty I fetch next set of 50 objects.
What I understand is NSArrayController calls the method objectInItemsAtIndex for only the visible rows in the table view. But the problem here is as soon as set the PRIList the objectInItemsAtIndex method is called for all the objects. This is even called when some selection is changed in table view (the stack trace shows this method is called from [_NSModelObservingTracker startObservingModelObjectAtReferenceIndex])
Basically I want to fetch the records whenever the user scrolls down in the table view.
I followed the same approach in a different project in Lion. It worked there. Currently I am in Mavericks.
I tried overriding the isCompatibleWithResponsiveScrolling in the custom table view and returned it to NO. Still no luck.
Any help is very much appreciated.
First, have you assigned or bound the sort descriptors of the array controller? Or set any columns to automatically generate sort descriptors? (I'm not sure that latter is relevant. It depends on whether the column is sorted by default.)
In any case, if the array controller feels the need to sort the objects in order to arrange the objects, then it will need to load all of the contents. I was under the impression that it always does so, anyway, although you report that it works.
For an issue like this, I'd recommend that you go for full manual control. That means not using bindings or an array controller. Use a data source.
I have suddenly encountered a strange problem when making updates to core data objects using UI controls bound to core data NSManagedObjects.
Symptoms are as follows:
- An OutlineView displays a list of hierarchical objects
- A Detailed view shows the data fields from the selected object, these include text fields, dates etc.
- When updates are made in the detailed view these are reflected in the OutlineView (e.g. diplayName is used in the OutlineView).
- However when I save the changes the managedObjectContext tells me there are no changes to be saved. So for some reason the UI is not letting the context know that things have changed.
- Given that the bindings are done in IB I assume that any changes in the UI would automatically be reflected in the managedObjectContext
- For some reason one of the fields seems to always result in the context recognising that changes have been made but not the others. This one field happens to be a popup list containing objects from another entity in the core data database.
If anyone has any inkling on what could be causing this - is there any way to monitor when UI changes are made, for example changing text in a text field, and whether these changes are propagated to the managedObjects.
EDIT
Found the problem - for some reason I had changed some of the properties from #dynamic to #synthesize in the objective-c classes for the core data entities. This was breaking things !
The IBOutlets need to be hooked up to the callbacks so that changes are known. They don't report changes unless you hook it up. So even though textField.text != oldText, it doesn't matter unless you take that update, save it to the entity, then see if it recognizes
I need to load data dynamically as a user scrolls through an NSTableView. For example, the table might display 50 rows, and as it scrolls further I need to fetch more data from the network. The number of of objects/rows is known beforehand, so I want the table to have the right number of rows from the start, but showing empty cells while data is loading.
I'm using Core Data so it's easy to connect the table to my model using bindings. This would also take care of cells being updated as data comes in and is parsed. I've tried to figure out how I could do this by subclassing NSArrayController but from what I can tell there is no information flowing from the table to the controller about which rows actually need data. Therefore, I'm thinking of implementing NSTableViewDataSource instead, where I can easily check if the table has scrolled beyond the rows for which data is available. On the other hand, I don't know if I will get cells automatically updating as easily with this solution.
In case anyone comes across this, here's my own answer:
Yes, you need to implement NSTableViewDataSource on a controller, observe changes on the data and call reloadData manually on the table when changes occur. The main reason for doing this is that you can defer loading of data until it's actually needed (when the table view scrolls). Using the data source protocol keeps you informed of which indexes are requested.
I have a question about Core Data. When starting my appliction, when is my data (which is stored automatically by Core Data) loaded into the NSArrayControllers? I want to modify it in the first place before the user can interact with it.
To be more specific: I have an NSArrayController for the entitity Playlist. Before the user can add new playlists or interact with the app at all, I want to modify the playlists programmatically. I tried windowControllerDidLoadNib: in my NSPersistentDocument (MyDocument.m) and awakeFromNib both in my NSPersistendDocument and the NSArrayController, but when I check in these methods with [[myArrayController arrangedObjects] count] I get 0 as result (the array controller's content is empty).
However, I actually have data stored and it is displayed to the user. I just do not know when and where I can modify it in the first place.
Thank your for any help.
Data is never "loaded" into the NSArrayController. The array controller is not an array itself. It does not contain or otherwise store data.
Instead, the array controller queries the object it is bound to for specific pieces of data only when that specific data is needed. This is especially true of Core Data in which managed objects are only fully instantiated when their attributes are accessed. The array controller moves data from an array type data structure to another object (usually an UI element.)
If you want to modify an existing store before it displays in the UI, you need to process the data before the array controller used by the UI is even initialized. If you're using NSPersistentDocument, then you can override readFromURL:ofType:error: to fetch and modify all your objects when the document is first opened. Alternatively, you can override the window controller's windowWillLoad or showWindow methods.
Regardless of where you do it, you must fetch all the managed objects you want to modify. You could programmatically create an array controller to do this but a fetch request is easier to micro manage if you have a large number of objects to modify.
You could try observing the "arrangedObjects" keypath of the controller and adding some logic to work that your array controller has been populated for the first time.
Another possible hook is implementing the awakeFromInsert/awakeFromFetch methods of your managed objects.