关于NSFetchedResultsController的一些用法

如何在iPhone等设备持久保存数据，需要用到Core Data，它能帮你快速而有效率的完成数据储存，Core Data 编程经常用到 NSFetchedResultsController这个类，刚开始不太了解这个类的用法，不过后来查看官方的说明文档，有一点小体会，所以现在写下来和大家一起分享讨论。

NSFetchedResultsController是用于高效获取Coredata内的数据，然后将获取的数据现实在是UITableView；

Coredata生成的xcdatamodeld文件是用于持久数据保持，也就是关机之后保存在xcdatamodeld里面的数据不会丢失，如果网上请求数据然后保存到 xcdatamodeld文件里面，那么 NSFetchedResultsController就自动从

NSManagedObjectContext ＊Context更新数据，然后刷新列表；

也是就是NSFetchedResultsController会自动更新Context的内容并且现实，同时它也作为一个提供给Coredata数据给用户的接口，下面贴下代码

- (void)setFetchedResultsController:(NSFetchedResultsController *)newfrc
{
NSFetchedResultsController *oldfrc = _fetchedResultsController;
if (newfrc != oldfrc) {
_fetchedResultsController = newfrc;
newfrc.delegate = self;
if ((!self.title || [self.title isEqualToString:oldfrc.fetchRequest.entity.name]) && (!self.navigationController || !self.navigationItem.title)) {
self.title = newfrc.fetchRequest.entity.name;
}
if (newfrc) {
if (self.debug) NSLog(@"[%@ %@] %@", NSStringFromClass([self class]), NSStringFromSelector(_cmd), oldfrc ? @"updated" : @"set");
[self performFetch];
} else {
if (self.debug) NSLog(@"[%@ %@] reset to nil", NSStringFromClass([self class]), NSStringFromSelector(_cmd));
[self.tableView reloadData];
}
}
}

#pragma mark - UITableViewDataSource

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

}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{

NSInteger rows = 0;
if ([[self.fetchedResultsController sections] count] > 0) {
id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
rows = [sectionInfo numberOfObjects];
}
return rows;

}

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
return [[[self.fetchedResultsController sections] objectAtIndex:section] name];
}

- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index
{
return [self.fetchedResultsController sectionForSectionIndexTitle:title atIndex:index];

}

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView
{
return [self.fetchedResultsController sectionIndexTitles];
}

#pragma mark - NSFetchedResultsControllerDelegate
//当Context将会改变内容执行该委托
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
[self.tableView beginUpdates];
}
//当该部分要被修改执行该委托
- (void)controller:(NSFetchedResultsController *)controller
didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
atIndex:(NSUInteger)sectionIndex
forChangeType:(NSFetchedResultsChangeType)type
{
switch(type)//判对是添加还是删除
{
NSLog(@"sectionIndex is %d",sectionIndex);
case NSFetchedResultsChangeInsert:
[self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;

case NSFetchedResultsChangeDelete:
[self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;
}
}

//当内容的对象被改变时候执行
- (void)controller:(NSFetchedResultsController *)controller
didChangeObject:(id)anObject
atIndexPath:(NSIndexPath *)indexPath
forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath
{
switch(type)
{
case NSFetchedResultsChangeInsert:
[self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;

case NSFetchedResultsChangeDelete:
[self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
break;

case NSFetchedResultsChangeUpdate:
[self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
break;

case NSFetchedResultsChangeMove:
[self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
[self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
}
}

//当内容修改完成执行
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
[self.tableView endUpdates];
}