MFetchedResultsController.swift

//some time, frc section may be need section offset
@objc public protocol MFetchedResultsControllerOffsetSectionDelegate{
    func offsetSection() -> Int
}

class MFetchedResultsController: NSFetchedResultsController, NSFetchedResultsControllerDelegate {
    weak var viewController: UIViewController?  //UITableViewController UICollectionViewController
    weak var scrollView: UIScrollView?          //TableView CollectionView
    
    weak var offsetSectionDelegate: MFetchedResultsControllerOffsetSectionDelegate?
    
    private var offsetSection: Int!
    
    var deletedSectionIndexes: NSMutableIndexSet!
    var insertedSectionIndexes: NSMutableIndexSet!
    
    var deletedRowIndexPaths: [NSIndexPath]!
    var insertedRowIndexPaths: [NSIndexPath]!
    var updatedRowIndexPaths: [NSIndexPath]!
    
    //if frc is alloc after viewWillAppear, you should set it to false menually
    var isViewInvisble: Bool = true
    
    //in viewWillAppear call
    func startListening(){

        //for first time viewWillAppear, unnecessary performFetch and reloadData
        if isViewInvisble {
            isViewInvisble = false
            return
        }
        
        if let _ = viewController {
                self.delegate = self
            
                do {
                    try self.performFetch()
                    
                    if let t = scrollView as? UITableView {
                        t.reloadData()
                    }else if let c = scrollView as? UICollectionView {
                        c.reloadData()
                    }
                } catch (_){
                    
                }
        }
    }
    
    //in viewWillDisappear call
    func endListening(){
        self.delegate = nil
    }
    
    // MARK: NSFetchedResultsControllerDelegate
    
    func controllerWillChangeContent(controller: NSFetchedResultsController){
        assert(viewController != nil, "viewController is nil")
        assert(scrollView != nil, "scrollView is nil")
        
        if viewController == nil || scrollView == nil || DataEnvironment.sharedDataEnvironment().notNeedUpdateVC == viewController || !viewController!.isViewLoaded() {
            return
        }
        
        print("FRC VC:", viewController);
        
        if let d = self.offsetSectionDelegate {
            offsetSection = d.offsetSection()
        }else{
            offsetSection = 0
        }
        
        insertedSectionIndexes = NSMutableIndexSet()
        deletedSectionIndexes = NSMutableIndexSet()
        
        insertedRowIndexPaths = [NSIndexPath]()
        deletedRowIndexPaths = [NSIndexPath]()
        updatedRowIndexPaths = [NSIndexPath]()
    }
    
    func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType){
        if viewController == nil || scrollView == nil || DataEnvironment.sharedDataEnvironment().notNeedUpdateVC == viewController || !viewController!.isViewLoaded() {
            return
        }
        
        switch type {
            case .Insert:
                self.insertedSectionIndexes.addIndex(sectionIndex+offsetSection)
            case .Delete:
                self.deletedSectionIndexes.addIndex(sectionIndex+offsetSection)
            default: break
        }
    }
    
    func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?){
        if viewController == nil || scrollView == nil || DataEnvironment.sharedDataEnvironment().notNeedUpdateVC == viewController || !viewController!.isViewLoaded() {
            return
        }
        
        print(type.rawValue, indexPath, newIndexPath)
        
        if let o = anObject as? NSManagedObject {
            print(o.entity.name)
        }
        
        switch type {
            case .Insert:
                if indexPath == nil { //fix iOS8 bug
                    let section = newIndexPath!.section+offsetSection
                    
                    //avoid insert row again if section inserted
                    if !self.insertedSectionIndexes.containsIndex(section) {
                        self.insertedRowIndexPaths!.append(NSIndexPath(forRow: newIndexPath!.row, inSection: newIndexPath!.section+offsetSection))
                    }
                }
            case .Delete:
                let section = indexPath!.section+offsetSection
                
                //avoid delete row again if section deleted
                if !self.deletedSectionIndexes.containsIndex(section) {
                    self.deletedRowIndexPaths.append(NSIndexPath(forRow: indexPath!.row, inSection: indexPath!.section+offsetSection))
                }
            case .Move:
                if let i = indexPath, nI = newIndexPath {
                    if i.row != nI.row || i.section != nI.section { //fix iOS9 bug
                        if !self.deletedSectionIndexes.containsIndex(i.section) {
                            self.deletedRowIndexPaths.append(NSIndexPath(forRow: i.row, inSection: i.section+offsetSection))
                        }
                        
                        if !self.insertedSectionIndexes.containsIndex(nI.section){
                            self.insertedRowIndexPaths.append(NSIndexPath(forRow: nI.row, inSection: nI.section+offsetSection))
                        }else{
                            assert(false, "there is another bug")
                        }
                    }
                }
            case .Update:
                let ip = NSIndexPath(forRow: indexPath!.row, inSection: indexPath!.section+offsetSection)
                self.updatedRowIndexPaths.append(ip)
        }
    }
    
    func controllerDidChangeContent(controller: NSFetchedResultsController){
        defer {
            //clean
            self.deletedSectionIndexes = nil
            self.insertedSectionIndexes = nil
            
            self.deletedRowIndexPaths = nil
            self.insertedRowIndexPaths = nil
            self.updatedRowIndexPaths = nil
        }
        
        if viewController == nil || scrollView == nil || DataEnvironment.sharedDataEnvironment().notNeedUpdateVC == viewController || !viewController!.isViewLoaded() {
            return
        }
        
        print("insert section: ", self.insertedSectionIndexes)
        print("delete section: ", self.deletedSectionIndexes)
        
        print("insert indpath: ", self.insertedRowIndexPaths)
        print("delete indpath: ", self.deletedRowIndexPaths)
        print("update indpath: ", self.updatedRowIndexPaths)
        
        //fix iOS8 bug: update and then move same indexPath
        self.updatedRowIndexPaths = self.updatedRowIndexPaths.filter {
            return !self.insertedSectionIndexes.contains($0.section) &&
                !self.deletedSectionIndexes.contains($0.section) &&
                !self.insertedRowIndexPaths.contains($0) &&
                !self.deletedRowIndexPaths.contains($0)
        }
        print("update indpath: ", self.updatedRowIndexPaths)
        
        let c = self.insertedSectionIndexes.count +
            self.deletedSectionIndexes.count +
            self.insertedRowIndexPaths.count +
            self.deletedRowIndexPaths.count +
            self.updatedRowIndexPaths.count
        
        if c > 0 { //fix iOS8/9 bug: count maybe 0
            if let tableView = scrollView as? UITableView {
                tableView.beginUpdates()
                
                //for section
                if self.deletedSectionIndexes.count > 0 {
                    tableView.deleteSections(self.deletedSectionIndexes, withRowAnimation: UITableViewRowAnimation.Automatic)
                }
                
                if self.insertedSectionIndexes.count > 0 {
                    tableView.insertSections(self.insertedSectionIndexes, withRowAnimation: UITableViewRowAnimation.Automatic)
                }
                
                //for row
                if self.updatedRowIndexPaths.count > 0 { //put update first
                    tableView.reloadRowsAtIndexPaths(self.updatedRowIndexPaths, withRowAnimation: UITableViewRowAnimation.None)
                }
                
                if self.deletedRowIndexPaths.count > 0 {
                    tableView.deleteRowsAtIndexPaths(self.deletedRowIndexPaths, withRowAnimation: UITableViewRowAnimation.Automatic)
                }
                
                if self.insertedRowIndexPaths.count > 0 {
                    tableView.insertRowsAtIndexPaths(self.insertedRowIndexPaths, withRowAnimation: UITableViewRowAnimation.Automatic)
                }
                
                tableView.endUpdates()
            }else if let collectionView = scrollView as? UICollectionView {
                collectionView.performBatchUpdates({ () -> Void in
                    if self.deletedSectionIndexes.count > 0 {
                        collectionView.deleteSections(self.deletedSectionIndexes)
                    }
                    
                    if self.insertedSectionIndexes.count > 0 {
                        collectionView.insertSections(self.insertedSectionIndexes)
                    }
                    
                    if self.deletedRowIndexPaths.count > 0 {
                        collectionView.deleteItemsAtIndexPaths(self.deletedRowIndexPaths)
                    }
                    
                    if self.insertedRowIndexPaths.count > 0 {
                        collectionView.insertItemsAtIndexPaths(self.insertedRowIndexPaths)
                    }
                    
                    if self.updatedRowIndexPaths.count > 0 {
                        collectionView.reloadItemsAtIndexPaths(self.updatedRowIndexPaths)
                    }
                    
                }, completion: { (_) -> Void in
                        
                })
            }
        }
    }
}

Wow, thank you so much for this! Very interestingly, you seem to have the exact same use case as me - I also need offsetSection since I combine two FRC delegates in one tableview.

Your iOS8/9 fixes are spot on, as far as I can tell - you found more than me. The thing you fixed in line 108 frustrated me today, and I couldn't find out why that was happening. So.. thanks!

I'm happy to report that your code also works with Obj-C with minor adjustments (XCode's Swift header generation is so crappy that I rather not experiment now which of my changes made it Obj-c compatible.. but I made the class public and added @objc public to the scrollView and offsetSectionDelegate vars).

@TonnyTao Shouldn't i.section on line 126 and nI.section on line 130 be i.section+offsetSection and nI.section+offsetSection respectively?