I am using an NSFetchedResultsController in my UITableViewController.
Is it possible to specify a predicate that will not retrieve items which have duplicate fields in x number of fields that I specify.
For example, I want to search all results for items but if the itemName AND itemDescription AND itemQuantity are the same, I want only one of these items.
Option 1
When the page loads do a single run through the data and keep a list of objectID that are duplicate. For duplicate object set the row height of the cell to be 0. So they are technically still there, but you can't see it. This make dealing with the NSFetchedResultsControllerDelegate calls easy because no indexPaths have changed
Option 2
If the dataset is always selected in the same way and an object that is a duplicate is always a duplicate you can set an 'isDuplicate' in the object and filter it out in the predicate. Or you can not store at all in the first place. If objects are displayed in different sets and in different way and sometime should be displayed and sometime not be displayed this is not a good solution
Option 3
If you are sorting by the same criteria that make an object duplicate (that is duplicates always appear right next to a non-duplicate) and you are NOT using sections, then you can use sectionKeyPath. SectionKeyPath groups items together into sections. Group the duplicate and non duplicate together and then display every section as a single row (use the first item in each section). The indexPaths of the fetchedResultsController will not match the indexPaths of the tableview so you have to careful to convert them.
Option 4
Instead of accessing the objects from a fetchedResultsController do a fetch and and filter the array. Then use the array to display the objects. The downside is that you don't get updates on when objects change. This can be especially problematic is objects are deleted, as accessing a managedObject that's entity was delete can lead to a crash.
I recommend option 1
Related
I have a UITableView and one of its sections is managed by a NSFetchedResultsController. It fetches core data objects and keep them sorted by the "order" attribute:
object with order 1
object with order 2
object with order 3
The requirement that I'm facing is that the user can move rows around. After move:
object with order 2
object with order 1
object with order 3
What do I need to do to ensure that the managed objects in core data reflect changes in order resulting from user moving table view rows around? When I'm working with GMGridView, there's a callback that exchanges two objects. In such case, changing their order works, but I do not see such function for a UITableView.
Would I need to manually change the order attribute for all objects that exist below the moved row?
You can use this:
- (NSIndexPath *) tableView:(UITableView *)tableView
targetIndexPathForMoveFromRowAtIndexPath:(NSIndexPath *)sourceIndexPath
toProposedIndexPath:(NSIndexPath *)proposedDestinationIndexPath
Plus re-ordering your data-source, by exchanging the objects order.
You need to store an association between the fetched object and the 'row order'. You order the rows based on row order; the row order defaults to your 'order' attribute. When the user moves a row, you update the 'row order' as well.
You can maintain the association either in the CoreData object itself (add another attribute) or by mapping the fetched object to its row order (in NSUserDefaults or in just a NSDictionary).
Moving rows around does not just affect the order attribute of itself but all the rows behind it. A work around I have found is to copy the fetch request objects to an nsmutablearray then moving the object within this array. Then running a for loop and updating the order attribute in each object then saving the managed object context. Then reload the uitableview. This seems like a lot of work but currently moving objects in a fetch request is not automatic like insert and delete. I hope this helps!
Is there any simple way to get the object, used to render given row in CellTable, by index of the row?
I am using AsyncDataProvider, and don't want to remember lists of data objects, returned from the server. Also I am using MultiSelectionModel, so several items could be selected there and I need to track out which one was clicked last.
I know the index of last clicked row, so I need to get the object, corresponding to the row, somehow.
getVisibleItem? possibly combined with getPageStart if you're using paging and you only know the absolute index.
For your use-case, maybe you could use a customized selection model whose setSelected tracks the last change.
Hey,
I'm basically trying to retrieve data from SQlite db and populate a tableView from it.
The sql-data-retrieval method creates two arrays. "dataArray" and "SectionArray".
DataArray is filled with data NSObjects.
Uptil this point, i can create the appropriate Section headers.
Here is the problem,
-1 What do i do to make sure that the right objects get into their appropriate sections and not under any other sections (which they seem to be doing). Also the Count(number of rows) in each section differs.
What should the code be in "NumberOfRowsAtIndexPath" and cellForRowAtIndexPath methods
-2 What kind of datasource objects are more suited for this type. I'm simply filling up two NSMutableArrays - dataArray(rows) and SectionArray(Section headers).
I think you should make many NSArray one for each table header you have created. In NumberOfRowsAtIndexPath you will return the count of the array for the requested section, and in cellForRowAtIndexPath you will choose your array using the section index (as before) and with the row index you will select the row of that array.
I thought that would be very common and easy iPhone App. In the main app I connect to database, retrieve values from database (NSDate converted to NSString)n and put into single array. Then in one of the views I populate UITableView with elements from the array. UITableView is grouped (sections). I step through array to discover number of sections (change section if new day). How do I retrieve correct element of array in cellForRowAtIndexPath? IndexPath.section and IndexPath.row seem useless as row starts count from zero for each section. If number of rows in each section was the same it would have been easy:
[arryData objectAtIndex:(indexPath.row)+indexPath.section*[tblMatchesView numberOfRowsInSection:indexPath.section]];
But number of rows in each section varies... :-)
Separate your data into arrays of arrays (based on the number of different days) once you get it from the database, that'd be the simplest solution...
How about storing different date sections in different arrays? For example, you can have an array A of array. You can loop through the original arrays yourself, if you found a new day, you just create a new array and put it into the array A. And then, when you loop over the cell, you can get the section number to get the correct array and based on the row number to get the correct elemenet in the array
It doesn't have absolute cursor but you can try utilizing
UILocalizedIndexedCollation class which is used to ease the "sectioning" of your data and proving the tableView delegate functions the required data such as the index titles, etc
Here's apple documentation link for it:
https://developer.apple.com/library/ios/#documentation/iPhone/Reference/UILocalizedIndexedCollation_Class/UILocalizedIndexedCollation.html#//apple_ref/occ/cl/UILocalizedIndexedCollation
What's the difference?
In my context, I need to be able to dynamically add to and remove objects. The user clicks on rows of a table that check on and off and thus add or remove the referenced object from the list.
A wild guess is that array has indexed items while set has no indexes?
An NSSet/NSMutableSet doesn't keep items in any particular order. An NSArray/NSMutableArray does store the items in a particular order. If you're building a table view, you should definitely use an array as your data source of choice.
Also, NSMutableSet makes sure that all objects are unique.
NSMutableArray goes well with UITableView since elements have index, so you can return [array count] to get number of table rows, or [array objectAtIndex:rowNumber] to easily associate element with row.
Also, according to the documentation, testing for object membership is faster with NSSets.
You can use sets as an alternative to arrays when the order of
elements isn’t important and performance in testing whether an object
is contained in the set is a consideration—while arrays are ordered,
testing for membership is slower than with sets.
Well there are 3 main differences. 1) Sets are unordered 2)Don't have an index & 3)Cannot have duplicate values where Arrays are ordered, indexed & can store duplicate values.