CoreData的使用（IOS学习）
——杂言：最近开始学习IOS7的开发，下文是在已经建好的项目里加入CoreData的结构，并实现一个基于coredata的简单save,query。
1. 引入Core Data Framework。选中项目-->Genaral-->Linked Frameworks and Libraries中添加“CoreData.Framework”。然后在prefix.pch中加入“#import<CoreData/CoreData.h>”
2. 加入数据模型，创建Model.xcdatamodeld文件。File-->New-->File-->IOS-->Core Data-->Data Model
3. 在Delegate中建立CoreData与Delegate的关联。点击XYZAppDelegate.h，在@interface与@end之中加入以下代码
1 @property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext; 2 @property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel; 3 @property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator; 4 5 - (void) saveContext; 6 - (NSURL *) applicationDocumentsDirectory;
4. 之后在XYZAppDelegate.m的@implementation下面写入以下代码（注：标红的2处名字请与.xcdatamodeld文件名保持一致）
1 @synthesize managedObjectContext = _managedObjectContext; 2 @synthesize managedObjectModel = _managedObjectModel; 3 @synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
1 - (void) saveContext 2 { 3 NSError *error = nil; 4 5 NSManagedObjectContext *managedObjectContext = self.managedObjectContext; 6 if(managedObjectContext != nil){ 7 if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) { 8 NSLog(@"Unresolved error%@, %@", error, [error userInfo]); 9 } 10 } 11 } 12 - (NSManagedObjectContext *) managedObjectContext 13 { 14 if (_managedObjectContext != nil) { 15 return _managedObjectContext; 16 } 17 NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator]; 18 if(coordinator != nil){ 19 NSLog(@"coordinator is not null-----"); 20 _managedObjectContext = [[NSManagedObjectContext alloc]init]; 21 [_managedObjectContext setPersistentStoreCoordinator:coordinator]; 22 }else{ 23 NSLog(@"coordinator is null-----"); 24 } 25 return _managedObjectContext; 26 } 27 - (NSManagedObjectModel *) managedObjectModel 28 { 29 if(_managedObjectModel != nil){ 30 return _managedObjectModel; 31 } 32 NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Ratings" withExtension:@"momd"]; 33 _managedObjectModel = [[NSManagedObjectModel alloc]initWithContentsOfURL:modelURL]; 34 return _managedObjectModel; 35 } 36 - (NSPersistentStoreCoordinator *) persistentStoreCoordinator 37 { 38 if(_persistentStoreCoordinator != nil){ 39 return _persistentStoreCoordinator; 40 } 41 NSURL *storeUrl = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Ratings.sqlite"]; 42 NSError *error = nil; 43 NSLog(@"storeUrl: %@",[self applicationDocumentsDirectory]); 44 _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc]initWithManagedObjectModel:[self managedObjectModel]]; 45 if(![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:nil error:&error]){ 46 NSLog(@"Unresolved error %@%@", error, [error userInfo]); 47 abort(); 48 } 49 return _persistentStoreCoordinator; 50 } 51 - (NSURL *) applicationDocumentsDirectory 52 { 53 return [[[NSFileManager defaultManager]URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask]lastObject]; 54 }
5. 至此，Core Data的准备工作已经完毕。
6. 现在可以创建Entity并结合使用，打开Ratings.xcdatamodeld文件，面板如下(2种模式)，可以点击并添加Entity(可以结合右侧属性面板使用)
7. 为entity添加.m和.h文件，File-->New->File->IOS->Core Data->NSManagedObject subclass
8. entity已经创建完成，可以开始在Controller中使用相关context操作。我的是XYZPlayersViewController。
9. XYZPlayersViewController.h中添加以下代码
1 @property (nonatomic, strong) NSManagedObjectContext *context;
10. XYZPlayersViewController.m中需要使用的地方添加以下代码
1 @synthesize context;
1 XYZAppDelegate *delegate = (XYZAppDelegate *)[[UIApplication sharedApplication]delegate]; 2 self.context = delegate.managedObjectContext; 3 4 Player *player = [NSEntityDescription insertNewObjectForEntityForName:@"Player" 5 inManagedObjectContext:context]; 6 player.name = @"timelyxyz"; 7 player.game = @"Chess"; 8 player.rating = [NSNumber numberWithInt:100]; 9 10 NSError *error = nil; 11 if(![context save:&error]){ 12 NSLog(@"%@", [error localizedDescription]); 13 } 14 15 NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]init]; 16 NSEntityDescription *entity = [NSEntityDescription entityForName:@"Player" 17 inManagedObjectContext:context]; 18 [fetchRequest setEntity:entity]; 19 20 NSArray *fetchObjects = [context executeFetchRequest:fetchRequest error:&error]; 21 for(NSManagedObject *info in fetchObjects){ 22 NSLog(@"name: %@",[info valueForKey:@"name"]); 23 NSLog(@"game: %@", [info valueForKey:@"game"]); 24 NSLog(@"rating: %@", [info valueForKey:@"rating"]); 25 }
11. log输出如下
demo下载：Ratings
