【发布时间】：2015-09-03 19:18:07
【问题描述】：
在我的另一个question 中，关于在Core Data 支持的UITableView 中添加插入行，我提到我的NSFetchedResultsController 将它获取的每个对象分配给我的UITableView 中的单独部分。我认为这只是默认行为，但 Marcus S. Zarra 说我的控制器配置或数据源委托方法可能有问题。我承认，我的代码感觉有点像弗兰肯斯坦，其中的部分来自 Apple 文档和大量教程。这是我的第一个程序，也是我第一次使用 Core Data，所以请温柔一点；）
我的table view controller的header如下：
#import <UIKit/UIKit.h>
#import "RubricAppDelegate.h"
@interface ClassList : UITableViewController {
NSMutableArray *classList;
NSFetchedResultsController *fetchedResultsController;
NSManagedObjectContext *managedObjectContext;
}
@property(nonatomic,retain) NSMutableArray *classList;
@property(nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
@property(nonatomic, retain) NSManagedObjectContext *managedObjectContext;
- (IBAction) grade:(id)sender;
@end
我的实现文件包含一堆虚拟测试数据。我包括在内，以防我使用不正确的方法来实例化 Core Data 对象。基本上，我想知道我的 NSFetchedResultsController 是否应该不将我的对象（在本例中为 myClass 的实例）返回到单独的部分中。如果是这样，我在做什么来制造这个问题？
目前的最终目标是让我能够在表格顶部添加一个插入单元格（我知道将它放在底部是“标准的”，但我喜欢它在应用程序中的外观反过来做）。您会注意到我的-tableView:editingStyleForRowAtIndexPath: 设置要插入的第 0 节的单元格样式，但当然我需要弄清楚如何在单元格 1 而不是单元格 0 开始列出 myClass.classTitle（这就是为什么我要确定是否将每个对象分配到自己的部分是正常的）。
这是我的实现文件：
#import "ClassList.h"
#import "ClassRoster.h"
#import "RubricAppDelegate.h"
#import "Student.h"
#import "myClass.h"
@implementation ClassList
@synthesize classList;
@synthesize fetchedResultsController;
@synthesize managedObjectContext;
#pragma mark -
#pragma mark View lifecycle
- (void)viewDidLoad {
[super viewDidLoad];
self.editing = YES;
RubricAppDelegate *appDelegate = (RubricAppDelegate *)[[UIApplication sharedApplication] delegate];
managedObjectContext = [appDelegate managedObjectContext];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"myClass" inManagedObjectContext:managedObjectContext];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entity];
//test data
myClass *newClass = (myClass *) [NSEntityDescription insertNewObjectForEntityForName:@"myClass" inManagedObjectContext:managedObjectContext];
newClass.classTitle = @"UFDN 1000";
NSNumber *ID = [NSNumber numberWithInt:1];
newClass.classID = ID;
Student *newStudent = (Student *) [NSEntityDescription insertNewObjectForEntityForName:@"Student" inManagedObjectContext:managedObjectContext];
newStudent.classID = ID;
newStudent.studentName = @"Andy Albert";
newStudent.studentUsername = @"albera";
[newClass addStudentsObject:newStudent];
newStudent.classID = ID;
newStudent.studentName = @"Bob Dole";
newStudent.studentUsername = @"doleb";
[newClass addStudentsObject:newStudent];
newStudent.classID = ID;
newStudent.studentName = @"Chris Hanson";
newStudent.studentUsername = @"hansoc";
[newClass addStudentsObject:newStudent];
myClass *newClass2 = (myClass *) [NSEntityDescription insertNewObjectForEntityForName:@"myClass" inManagedObjectContext:managedObjectContext];
newClass2.classTitle = @"UFDN 3100";
ID = [NSNumber numberWithInt:2];
newClass2.classID = ID;
newStudent.classID = ID;
newStudent.studentName = @"Danny Boy";
newStudent.studentUsername = @"boyd";
[newClass2 addStudentsObject:newStudent];
newStudent.classID = ID;
newStudent.studentName = @"James Matthews";
newStudent.studentUsername = @"matthj";
[newClass2 addStudentsObject:newStudent];
newStudent.classID = ID;
newStudent.studentName = @"Aaron Todds";
newStudent.studentUsername = @"toddsa";
[newClass2 addStudentsObject:newStudent];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"classID" ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
[request setSortDescriptors:sortDescriptors];
[sortDescriptor release];
NSError *error;
fetchedResultsController = [[NSFetchedResultsController alloc]
initWithFetchRequest:request
managedObjectContext:self.managedObjectContext
sectionNameKeyPath:@"classTitle" cacheName:nil];
[fetchedResultsController performFetch:&error];
UIBarButtonItem *gradeButton = [[UIBarButtonItem alloc]
initWithTitle:@"Grade"
style:UIBarButtonItemStylePlain
target:self
action:@selector(grade:)];
self.navigationItem.rightBarButtonItem = gradeButton;
[gradeButton release];
}
- (IBAction) grade:(id)sender {
}
#pragma mark -
#pragma mark Table view data source
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
NSLog(@"Number of sections = %d", [[fetchedResultsController sections] count]);
return ([[fetchedResultsController sections] count]);
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
// Return the number of rows in the section.
id <NSFetchedResultsSectionInfo> myClass = [[fetchedResultsController sections] objectAtIndex:section];
NSLog(@"Number of classes = %d", [myClass numberOfObjects]);
return [myClass numberOfObjects];
}
// Customize the appearance of table view cells.
- (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];
myClass *theClass = [fetchedResultsController objectAtIndexPath:indexPath];
NSLog(@"Class name is: %@", theClass.classTitle);
cell.textLabel.text = theClass.classTitle;
}
return cell;
}
- (UITableViewCellEditingStyle)tableView:(UITableView *)tableView editingStyleForRowAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath.section == 0) {
return UITableViewCellEditingStyleInsert;
}
else return UITableViewCellEditingStyleDelete;
}
// Override to support editing the table view.
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
if (editingStyle == UITableViewCellEditingStyleDelete) {
myClass *result = (myClass *)[fetchedResultsController objectAtIndexPath:indexPath];
[managedObjectContext deleteObject:result];
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:YES];
}
else if (editingStyle == UITableViewCellEditingStyleInsert) {
}
}
#pragma mark -
#pragma mark Table view delegate
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
// Navigation logic may go here. Create and push another view controller.
/*
<#DetailViewController#> *detailViewController = [[<#DetailViewController#> alloc] initWithNibName:@"<#Nib name#>" bundle:nil];
// ...
// Pass the selected object to the new view controller.
[self.navigationController pushViewController:detailViewController animated:YES];
[detailViewController release];
*/
}
#pragma mark -
#pragma mark Memory management
- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];
// Relinquish ownership any cached data, images, etc that aren't in use.
}
- (void)viewDidUnload {
// Relinquish ownership of anything that can be recreated in viewDidLoad or on demand.
// For example: self.myOutlet = nil;
}
- (void)dealloc {
[classList release];
[super dealloc];
}
@end
我的 RubricAppDelegate 与用于设置 Core Data NSManagedObjectContext、NSPersistentStoreCoordinator 等的 Apple 文档基本相同。但是，如果您认为其中可能存在问题，请告诉我，我会发布它。
编辑：我忘了提到我知道每个对象被分配到不同部分的两个原因。
1) NSLog(@"Number of sections = %d", [[fetchedResultsController sections] count]); 内的 -numberOfSectionsInTableView: 返回我拥有的 myClass 对象的数量。
2) 如果我将-numberOfSectionsInTableView: 设置为返回 1，我的表格将只显示一个对象，而将其余对象删除。
【问题讨论】：
标签： uitableview core-data nsfetchedresultscontroller