Question

我有一个示例应用，其中包含一个NSManagedObject（让我们称之为类CustomObject），只有一个属性。

该应用有一个简单的用户界面，其中包含一个UICollectionView视图控制器，使用NSFetchedResultsController作为基础数据源。 NSFetchedResultsController也设置为使用视图控制器作为NSFetchedResultsControllerDelegate委托。此外，我还有一些工具栏，其中包含一些按钮，用于添加/删除CustomObject个项目。

一个按钮将导致创建10,000 CustomObject个实体。我希望能够按下此按钮，一旦实体保存到磁盘/准备使用，UICollectionView应该更新以反映新值。我100％意识到会有某种延迟 - 像这样的保存值不是即时的 - 我希望在后台线程上发生延迟以防止UI锁定！

尽管我从我能说的内容中正确设置，但每当我实现三个“重要”NSFetchedResultsControllerDelegate方法中的任何一个时，我都会遇到UI延迟。 UI滞后持续时间根据数据存储中的CustomObject个数而有所不同。例如，如果我刚刚添加了前10,000个，则只有少量滞后，不到1秒。如果我已经添加了50,000 CustomObject s，则滞后更加明显，并且在某些情况下持续超过5-10秒。

正如我所说，当我实施controllerWillChangeContent，controller:didChangeObject:atIndexPath:forChangeType:newIndexPath或controllerDidChangeContent方法时，UI滞后才出现。即使在方法中没有实际实现，只是它在视图控制器中的事实使插入变慢。

知道我做错了什么吗？有没有解决的办法？这是一些代码：

CoreDataController.m - 负责设置核心数据堆栈

//
//  CoreDataController.m
//  CoreDataTestApp
//
//  Created by ZOlbrys on 4/12/18.
//  Copyright © 2018 ZOlbrys. All rights reserved.
//

#import "CoreDataController.h"
#import <UIKit/UIKit.h>

@interface CoreDataController()

@property (nonatomic, strong) NSURL *persistentStoreURL;
@property (nonatomic, strong) NSURL *managedObjectModelURL;

@property (nonatomic, strong, readwrite) NSPersistentStoreCoordinator *persistentStoreCoordinator;
@property (nonatomic, strong) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, strong, readwrite) NSManagedObjectContext *managedObjectContext;

@end

@implementation CoreDataController

+ (CoreDataController *)sharedController {
    static CoreDataController *sharedController;

    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{
        NSURL *managedObjectModelURL = [NSURL fileURLWithPath:[[NSBundle bundleForClass:[self class]] pathForResource:@"CoreDataTestApp" ofType:@"momd"]];

        NSString *applicationDocumentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
        NSURL *persistentStoreURL = [NSURL fileURLWithPath:[applicationDocumentsDirectory stringByAppendingPathComponent:@"CoreDataTestApp.sqlite"]];

        sharedController = [[CoreDataController alloc] initWithManagedObjectModelURL:managedObjectModelURL persistentStoreURL:persistentStoreURL];
    });

    return sharedController;
}

- (instancetype)initWithManagedObjectModelURL:(NSURL*)managedObjectModelURL persistentStoreURL:(NSURL*)persistentStoreURL {
    self = [super init];

    if (self) {
        self.persistentStoreURL = persistentStoreURL;
        self.managedObjectModelURL = managedObjectModelURL;

        [self setupCoreDataStack];
    }

    return self;
}

- (void)setupCoreDataStack {
    // setup managed object model
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:self.managedObjectModelURL];

    // setup persistent store coordinator
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:self.managedObjectModel];
    [_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:self.persistentStoreURL options:nil error:nil];

    // setup MOC
    _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    [_managedObjectContext setPersistentStoreCoordinator:self.persistentStoreCoordinator];
}

@end

ViewController.m - 负责，查看控制器的东西！

//
//  ViewController.m
//  CoreDataTestApp
//
//  Created by ZOlbrys on 4/12/18.
//  Copyright © 2018 ZOlbrys. All rights reserved.
//

#import "ViewController.h"
#import "CustomCell.h"
#import "CoreDataController.h"
#import "CustomObject+CoreDataClass.h"

static NSString *const CUSTOM_CELL_REUSE_IDENTIFIER = @"CUSTOM_CELL_REUSE_IDENTIFIER";

@interface ViewController ()<UICollectionViewDataSource, UICollectionViewDelegate, NSFetchedResultsControllerDelegate>

@property (strong, nonatomic) IBOutlet UICollectionView *collectionView;
@property (strong, nonatomic) NSFetchedResultsController *fetchedResultsController;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.collectionView.dataSource = self;
    self.collectionView.delegate = self;

    [self setupFetchedResultsController];
}

- (void)setupFetchedResultsController {
    NSFetchRequest<CustomObject *> *fetchRequest = [CustomObject fetchRequest];
    fetchRequest.sortDescriptors = @[ [[NSSortDescriptor alloc] initWithKey:@"identifier" ascending:YES] ];

    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:[CoreDataController sharedController].managedObjectContext sectionNameKeyPath:nil cacheName:nil];

    self.fetchedResultsController.delegate = self;

    [self.fetchedResultsController performFetch:nil];

    [self.collectionView reloadData];
}

- (void)addObjects:(NSUInteger)objectCount {
    NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    temporaryContext.parentContext = [CoreDataController sharedController].managedObjectContext;

    [temporaryContext performBlock:^{
        for (int i = 0; i < objectCount; i++) {
            CustomObject *object = [NSEntityDescription insertNewObjectForEntityForName:@"CustomObject" inManagedObjectContext:temporaryContext];
            object.identifier = [[NSUUID UUID] UUIDString];
        }

        NSError *error;
        if (![temporaryContext save:&error]) {
            NSLog(@"Error: %@", error);
        }

        [[CoreDataController sharedController].managedObjectContext performBlock:^{
            NSError *error;
            if (![[CoreDataController sharedController].managedObjectContext save:&error]) {
                NSLog(@"Error: %@", error);
            }
        }];
    }];
}

- (void)removeObjects:(NSUInteger)objectCount {
    NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    temporaryContext.parentContext = [CoreDataController sharedController].managedObjectContext;

    [temporaryContext performBlock:^{
        NSFetchRequest<CustomObject *> *fetchRequest = [CustomObject fetchRequest];
        fetchRequest.sortDescriptors = @[ [[NSSortDescriptor alloc] initWithKey:@"identifier" ascending:YES] ];
        fetchRequest.fetchLimit = objectCount;

        NSFetchedResultsController<CustomObject *> *fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:temporaryContext sectionNameKeyPath:nil cacheName:nil];

        [fetchedResultsController performFetch:nil];

        for (CustomObject *object in fetchedResultsController.fetchedObjects) {
            [temporaryContext deleteObject:object];
        }

        NSError *error;
        if (![temporaryContext save:&error]) {
            NSLog(@"Error: %@", error);
        }

        [[CoreDataController sharedController].managedObjectContext performBlock:^{
            NSError *error;
            if (![[CoreDataController sharedController].managedObjectContext save:&error]) {
                NSLog(@"Error: %@", error);
            }
        }];
    }];
}

- (IBAction)add10k:(id)sender {
    [self addObjects:10000];
}

- (IBAction)add1:(id)sender {
    [self addObjects:1];
}

- (IBAction)refetchData:(id)sender {
    [self.fetchedResultsController performFetch:nil];

    [self.collectionView reloadData];
}

- (IBAction)remove1:(id)sender {
    [self removeObjects:1];
}

- (IBAction)remove10k:(id)sender {
    [self removeObjects:10000];
}

#pragma mark UICollectionViewDataSource

- (NSInteger)collectionView:(nonnull UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return [self.fetchedResultsController.sections objectAtIndex:section].numberOfObjects;
}

- (nonnull __kindof UICollectionViewCell *)collectionView:(nonnull UICollectionView *)collectionView cellForItemAtIndexPath:(nonnull NSIndexPath *)indexPath {
    CustomCell* cell = [collectionView dequeueReusableCellWithReuseIdentifier:CUSTOM_CELL_REUSE_IDENTIFIER forIndexPath:indexPath];

    [cell setDisplayText:@"TODO"];

    cell.backgroundColor = [UIColor blueColor];

    return cell;
}

#pragma mark NSFetchedResultsControllerDelegate

//- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
//    // TODO
//}
//
//- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
//    // TODO
//}
//
//- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
//    // TODO
//}

@end

当然，我做了一些分析 - 上面没有注释controllerWillChangeContent，我看到了：

这不是我的代码 - 它是内部Apple代码......

这是显示此问题的项目的github链接：

Sample Core Data project

Answer 1

滞后似乎与所选的核心数据堆栈有关：

[协调员]←[主要背景]←[私人背景]

使用此体系结构，私有上下文中的每个提取/保存操作都将通过主上下文进行，然后阻止UI。更好的选择可能是交换上下文：

[协调员]←[私人语境]←[主要背景]

这一次，私有上下文操作不会阻止UI。

另一个选择是将两个上下文绑定到协调器：

[私人语境]→[协调员]←[主要背景]

使用这两种解决方案，如果需要，您需要将更新的对象合并回主要上下文，以便＆＃34;参见＆＃34;来自UI的变化。

添加多个对象时，NSFetchedResultsControllerDelegate实现导致UI滞后

1 个答案: