我已经使用核心数据UITableView填充了NSFetchedResultsController。我现在已经在视图中添加了UISegmentedControl，当您更改当前细分时，我希望更改tableview的内容。
我在网上读到，使用两个不同的NSFetchedResultsControllers是明智的，因为我可以从内置缓存中受益。唯一的问题是我似乎无法找到任何示例代码来执行此操作，并且不知道从哪里开始。
任何人都可以解释在创建第二个NSFetchedResultsController时从哪里开始，并根据分段控件更改tableview的哪些来源？
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;
查看实施代码：
@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。感谢。
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;
查看实施代码：
@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;
}
答案 0 :(得分：8)
您可以添加另一个表示当前所选NSFetchedResultsController的实例变量。当UISegmentedControl更改时更新此ivar。
这可能是由段
的valuechange事件触发的操作- (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：
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return [[self.currentFetchedResultsController sections] count];
}
并且您必须确保只有当前的nsfrc在NSFetchedResultsControllerDelegate方法中触发tableview更新。所以你必须改变所有这些。
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
if (controller == self.currentFetchedResultsController) {
[self.tableView beginUpdates];
}
}
但另外两个fetchedResultsControllers应该有这样一个延迟加载的getter。
- (NSFetchedResultsController *)competitorFetchedResultsController {
if (!myCompetitorFetchedResultsController) {
// create competitorFetchedResultsController
}
return myCompetitorFetchedResultsController;
}
- (NSFetchedResultsController *)keyphraseFetchedResultsController {
if (!myKeyphraseFetchedResultsController) {
// create keyphraseFetchedResultsController
}
return myKeyphraseFetchedResultsController;
}
然后切换为：
self.currentFetchedResultsController = self.keyphraseFetchedResultsController;
或
self.currentFetchedResultsController = self.competitorFetchedResultsController;