NSFetchedResultsController实现

Question

我使用的是核心数据和NSFetchedResultsController。有什么可以改进的吗？

//
//  RoutineTableViewController.m
//  App
//
//  Created by Me on 3/21/11.
//  Copyright 2011 __MyCompanyName__. All rights reserved.
//

#import "RoutineTableViewController.h"
#import <QuartzCore/QuartzCore.h>
#import "FlurryAnalytics.h"
#import "RoutineDayTableViewController.h"
#import "Routine.h"
#import "Exercise.h"
#import "DataModelController.h"


@implementation RoutineTableViewController

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:YES];
    self.fetchedResultsController = nil;
    [self.fetchedResultsController performFetch:nil];
    [self toggleEditButton];
}


- (void)viewDidLoad {
    [super viewDidLoad];

    [FlurryAnalytics logEvent:@"Routine"];

    if (!self.managedObjectContext) {
        self.managedObjectContext = [(MyAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; 
    }

    self.navigationItem.title = @"Routines";
    self.routineTableView.rowHeight = 65;
    self.routineTableView.delegate = self;
    self.routineTableView.backgroundColor = [UIColor clearColor];
    self.view.backgroundColor = [UIColor myBackgroundColor];

    self.navigationItem.leftBarButtonItem = self.editButtonItem;    
    self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(presentCreateRoutineAlert)];

    [self toggleEditButton];
}


- (void)toggleEditButton {
    if (!self.fetchedResultsController.fetchedObjects.count > 0) {
        self.navigationItem.leftBarButtonItem.enabled = NO;
    } else {
        self.navigationItem.leftBarButtonItem.enabled = YES;
    }
}


-(void)presentCreateRoutineAlert {    
    UIAlertView *anAlert = [[UIAlertView alloc]initWithTitle:@"Add Routine" message:@"Enter name for routine" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"Create", nil];
    [anAlert setAlertViewStyle:UIAlertViewStylePlainTextInput];
    [anAlert show];
}


- (void)alertView:(UIAlertView *)iAlertView willDismissWithButtonIndex:(NSInteger)iButtonIndex {
    if (iButtonIndex != [iAlertView cancelButtonIndex]) {
        NSString *aRoutineName = [iAlertView textFieldAtIndex:0].text;
        [self createRoutineWithName:aRoutineName];
    }
}


-(void)createRoutineWithName:(NSString *)iRoutineName {
    Routine *aRoutine = [DataModelController createRotuineWithName:iRoutineName];
    [self.routineTableView reloadData];
    [self pushToListForRoutine:aRoutine];
}


-(void)pushToListForRoutine:(Routine *)iRoutine {
    RoutineDayTableViewController *detailViewController = [[RoutineDayTableViewController alloc] initWithNibName:@"RoutineDayTableViewController" bundle:nil withRoutine:iRoutine];
    detailViewController.hidesBottomBarWhenPushed = YES;
    [self.navigationController pushViewController:detailViewController animated:YES];
}


#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}


- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
    return [sectionInfo numberOfObjects];
}


- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
    cell.imageView.image = [UIImage imageNamed:@"44-shoebox.png"];
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    cell.backgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"newcell.png"]];
    cell.textLabel.backgroundColor = [UIColor clearColor];
    cell.detailTextLabel.backgroundColor = [UIColor clearColor];
    cell.textLabel.font = [UIFont textLabelFontBig];

    Routine *aRoutine = (Routine *)[self.fetchedResultsController objectAtIndexPath:indexPath];
    cell.textLabel.text = aRoutine.name;
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [self.routineTableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
    }

    [self configureCell:cell atIndexPath:indexPath];

    return cell;
}


- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath {
    return YES;
}


- (void)setEditing:(BOOL)editing animated:(BOOL)animate {
    [self.routineTableView setEditing: !self.routineTableView.editing animated:YES];

    if (self.routineTableView.editing)
        [self.navigationItem.leftBarButtonItem setTitle:@"Done"];
    else
        [self.navigationItem.leftBarButtonItem setTitle:@"Edit"];
}


- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
     if (editingStyle == UITableViewCellEditingStyleDelete) {
         NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
         [context deleteObject:[self.fetchedResultsController objectAtIndexPath:indexPath]];

         NSError *error = nil;

         if (![self.managedObjectContext save:&error]) {
             NSLog(@"error: %@", error);
         }
     }
}


- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath {
    return YES;
}


#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    Routine *aRoutine = (Routine *)[self.fetchedResultsController objectAtIndexPath:indexPath];
    [self pushToListForRoutine:aRoutine];
    [tableView deselectRowAtIndexPath:indexPath animated:YES];
}


#pragma mark - Fetched results controller


- (NSFetchedResultsController *)fetchedResultsController {
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Routine" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"timeStamp" ascending:YES];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];

    [fetchRequest setFetchBatchSize:20];

    NSFetchedResultsController *theFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    NSError *error = nil;
    if (![theFetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return _fetchedResultsController;
}


#pragma mark - Fetched results controller delegate


- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
    [self.routineTableView beginUpdates];
}


- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    [self.routineTableView endUpdates];
    [self toggleEditButton];
}


- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type {
    switch(type) {
        case NSFetchedResultsChangeInsert:
            [self.routineTableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationAutomatic];
            break;
        case NSFetchedResultsChangeDelete:
            [self.routineTableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationAutomatic];
            break;
    }
}


- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
    UITableView *tableView = self.routineTableView;

    switch(type) {
        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            break;
        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            break;
        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
            break;
        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationAutomatic];
            break;
    }
}


@end

Answer 1

简单地看一下表视图控制器代码，我通常会建议一种更有效的配置单元格的方法。你有：

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
    cell.imageView.image = [UIImage imageNamed:@"44-shoebox.png"];
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    cell.backgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"newcell.png"]];
    cell.textLabel.backgroundColor = [UIColor clearColor];
    cell.detailTextLabel.backgroundColor = [UIColor clearColor];
    cell.textLabel.font = [UIFont textLabelFontBig];

    Routine *aRoutine = (Routine *)[self.fetchedResultsController objectAtIndexPath:indexPath];
    cell.textLabel.text = aRoutine.name;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [self.routineTableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
    }

    [self configureCell:cell atIndexPath:indexPath];
    return cell;
}

这意味着每次请求单元格时都会运行configureCell:atIndexPath:，每当用户滚动表时就会发生这种情况。这种方法中的大部分工作只需要在创建新单元时才能完成，这在每个用户滚动过程中都不一定发生(因为单元格是循环的)。

..。特别是在这个方法中创建一个新的UIImageView，这是不必要的。看起来只有这一行：

cell.textLabel.text = aRoutine.name;

每次请求单元格时都需要运行，因为名称可以更改。因此，我会将代码移出configureCell:atIndexPath:，并将您的代码更改为：

   - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
        static NSString *CellIdentifier = @"Cell";

        UITableViewCell *cell = [self.routineTableView dequeueReusableCellWithIdentifier:CellIdentifier];

        if (!cell) {
            cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
            [self configureCell:cell atIndexPath:indexPath];
        }

        // update the cell label for this specific routine name:
        Routine *aRoutine = (Routine *)[self.fetchedResultsController objectAtIndexPath:indexPath];
        cell.textLabel.text = aRoutine.name;

        return cell;
    }

现在，按照我们使用configureCell:atIndexPath:的方式，将其重命名为initializeCell:atIndexPath:之类可能会更清楚。此外，如果该方法中的代码太多，我可能建议创建一个UITableViewCell的新子类，并将所有这些代码放入其initWithStyle:reuseIdentifier:方法中，这样就可以从表视图控制器中完全删除对configureCell:atIndexPath:的调用。

但是，这将是一个代码模块化/整洁的问题。我提出的关于不每次调用configureCell:atIndexPath:的第一点实际上是一个性能问题。