在 SegmentedControl 更改上更改 NSFetchedResultsController [英] Change NSFetchedResultsController on SegmentedControl change

问题描述

我有一个 UITableView，它使用核心数据 NSFetchedResultsController 填充.我现在在视图中添加了一个 UISegmentedControl，当您更改当前段时，我希望 tableview 的内容也发生更改.

I've got a UITableView which is filled using a Core Data NSFetchedResultsController. I've now added a UISegmentedControl to the view and when you change the current segment, I'd like the contents of the tableview to change.

我在网上读到，使用两个不同的 NSFetchedResultsControllers 是明智的，这样我就可以从内置缓存中受益.唯一的问题是我似乎找不到执行此操作的任何示例代码，也不知道从哪里开始.

I've read around online that it would be wise to use two different NSFetchedResultsControllers as then I can benefit from the built-in caching. Only problem is I can't seem to find any sample code for doing this and don't know where to begin.

谁能解释从哪里开始创建第二个 NSFetchedResultsController 并根据分段控件更改 tableview 的来源?

Can anyone explain where to begin in creating a second NSFetchedResultsController and changing which sources the tableview based on the segmented control?

查看标题代码:

#import <CoreData/CoreData.h>

@interface DomainViewController : UIViewController <NSFetchedResultsControllerDelegate, UITableViewDataSource, UITableViewDelegate> {

    UITableView *domainView;
    UISegmentedControl *segmentedControl;
    NSString *domain;

}

@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain) NSString *domain;

@property (nonatomic, retain) IBOutlet UITableView *domainView;
@property (nonatomic, retain) IBOutlet UISegmentedControl *segmentedControl;

- (IBAction)segmentedControlIndexChanged;

查看实现代码:

@interface DomainViewController ()
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
@end

@implementation DomainViewController

@synthesize fetchedResultsController = __fetchedResultsController;
@synthesize managedObjectContext = __managedObjectContext;
@synthesize domain;
@synthesize domainView;
@synthesize segmentedControl;

- (void)viewDidLoad
{
    [super viewDidLoad];

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

}

- (IBAction)segmentedControlIndexChanged
{
    switch(self.segmentedControl.selectedSegmentIndex){
        case 0:
            break;
        case 1:
            break;
        default:
            break;
    }
}

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath
{
    NSManagedObject *managedObject = [self.fetchedResultsController objectAtIndexPath:indexPath];
    cell.textLabel.text = [[managedObject valueForKey:@"Keyphrase"] description];
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return [[self.fetchedResultsController sections] count];
}

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

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

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }

    // Configure the cell.
    [self configureCell:cell atIndexPath:indexPath];
    return cell;
}

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

    /*
     Set up the fetched results controller.
     */
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Result" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    // Set the batch size to a suitable number.
    [fetchRequest setFetchBatchSize:20];

    // Edit the sort key as appropriate.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"Keyphrase" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];

    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    [aFetchedResultsController release];
    [fetchRequest release];
    [sortDescriptor release];
    [sortDescriptors release];

    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error])
    {
        /*
         Replace this implementation with code to handle the error appropriately.

         abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return __fetchedResultsController;
}

非常感谢任何帮助.谢谢.

Any help is much appreciated. Thanks.

更新:更新代码

查看标题代码:

@property (nonatomic, retain) NSFetchedResultsController *currentFetchedResultsController;
@property (nonatomic, retain) NSFetchedResultsController *competitorFetchedResultsController;
@property (nonatomic, retain) NSFetchedResultsController *keyphraseFetchedResultsController;

查看实现代码:

@synthesize currentFetchedResultsController = __fetchedResultsController;
@synthesize competitorFetchedResultsController;
@synthesize keyphraseFetchedResultsController;

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

    /*
     Set up the fetched results controller.
     */
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Result" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    // Set the batch size to a suitable number.
    [fetchRequest setFetchBatchSize:20];

    // Edit the sort key as appropriate.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"Keyphrase" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];

    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    aFetchedResultsController.delegate = self;
    //self.fetchedResultsController = aFetchedResultsController;
    self.currentFetchedResultsController = aFetchedResultsController;

    [aFetchedResultsController release];
    [fetchRequest release];
    [sortDescriptor release];
    [sortDescriptors release];

    NSError *error = nil;
    //if (![self.fetchedResultsController performFetch:&error])
    if (![self.currentFetchedResultsController performFetch:&error])
    {
        /*
         Replace this implementation with code to handle the error appropriately.

         abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return __fetchedResultsController;
} 

推荐答案

您可以添加另一个实例变量来表示当前选定的 NSFetchedResultsController.当 UISegmentedControl 更改时更新此 ivar.

You could add another instance variable that represents the currently selected NSFetchedResultsController. And when the UISegmentedControl changes update this ivar.

这可能是段的 valuechange 事件触发的动作

this could be the action that is triggered by the valuechange event of the segment

- (IBAction *)segmentChanged:(UISegmentedControl *)sender {
    if ([sender selectedSegmentIndex] == 0) {
        self.currentFetchedResultsController = self.nsfrc1;
        [self.tableView reloadData];
    }
    else if ([sender selectedSegmentIndex] == 1) {
        self.currentFetchedResultsController = self.nsfrc2;     
        [self.tableView reloadData];
    }
}

以一个 UITableViewDataSource 方法为例:

one UITableViewDataSource method as example:

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return [[self.currentFetchedResultsController sections] count];
}

并且您必须确保只有当前的 nsfrc 会触发 NSFetchedResultsControllerDelegate 方法中的 tableview 更新.所以你也必须全部改变.

and you have to make sure that only the current nsfrc triggers a tableview update in the NSFetchedResultsControllerDelegate methods. So you have to change all of them too.

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
    if (controller == self.currentFetchedResultsController) {
        [self.tableView beginUpdates];
    } 
}

<小时>

不，你做错了.currentFetchedResultsController 只是一个 ivar，没有延迟加载 getter.它只是"指向当前使用的控制器的指针.

---

Nope, you are doing it wrong. the currentFetchedResultsController is just an ivar, without a lazy loading getter. It's "just" a pointer to the currently used controller.

但是另外两个fetchedResultsControllers应该有这样的延迟加载getter.

But the two other fetchedResultsControllers should have such a lazy loading getter.

- (NSFetchedResultsController *)competitorFetchedResultsController {
    if (!myCompetitorFetchedResultsController) {
        // create competitorFetchedResultsController
    }
    return myCompetitorFetchedResultsController;
}

- (NSFetchedResultsController *)keyphraseFetchedResultsController {
    if (!myKeyphraseFetchedResultsController) {
        // create keyphraseFetchedResultsController
    }
    return myKeyphraseFetchedResultsController;
}

然后切换:

self.currentFetchedResultsController = self.keyphraseFetchedResultsController;

或

self.currentFetchedResultsController = self.competitorFetchedResultsController;

这篇关于在 SegmentedControl 更改上更改 NSFetchedResultsController的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！