iOS开发学习之Core Data

3.创建NSManagedObject的子类，这里命名为Location（若没有实体属性类型是Transformable或没有额外的方法，只需要存储基本类型的话，可略过）

　　注意：这里可以做一个额外的工作，在Location+CoreDataProperties.h文件中，将实体属性类型是Transformable对应的@property属性的类型从id改为需要的类型

4.在AppDelegate.m文件添加以下代码：

@interface AppDelegate ()

@property (nonatomic,strong) NSManagedObjectContext *managedObjectContext;

@property (nonatomic,strong) NSManagedObjectModel *managedObjectModel;

@property (nonatomic,strong) NSPersistentStoreCoordinator *persistentStoreCoordinator;

@end

5.在AppDelegate.m文件的@implementation底部添加以下代码：

#pragma mark - Core Data

-(NSManagedObjectModel *)managedObjectModel

{

if(_managedObjectModel == nil)

{

NSString *modelPath = [[NSBundle mainBundle] pathForResource:@"DataModel" ofType:@"momd"];//这里的DataModel与第1步创建的文件名对应

NSURL *modelURL = [NSURL fileURLWithPath:modelPath];

_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];

}

return _managedObjectModel;

}

-(NSString *)documentsDirectory

{

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *documentsDirectory = [paths lastObject];

//NSLog(@"%@",documentsDirectory);

return documentsDirectory;

}

-(NSString *)dataStorePath

{

return [[self documentsDirectory] stringByAppendingPathComponent:@"DataStore.sqlite"];

}

-(NSPersistentStoreCoordinator *)persistentStoreCoordinator

{

if(_persistentStoreCoordinator == nil)

{

NSURL *storeURL = [NSURL fileURLWithPath:[self dataStorePath]];

_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:self.managedObjectModel];

NSError *error;

if(![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error])

{

NSLog(@"Error adding persistent store %@,%@",error,[error userInfo]);

abort();

}

return _persistentStoreCoordinator;

}

-(NSManagedObjectContext *)managedObjectContext

{

if(_managedObjectContext == nil)

{

NSPersistentStoreCoordinator *coordinator = self.persistentStoreCoordinator;

if(coordinator != nil)

{

_managedObjectContext = [[NSManagedObjectContext alloc] init];

[_managedObjectContext setPersistentStoreCoordinator:coordinator];

}

return _managedObjectContext;

}

6.在需要应用Core Data进行数据操控的视图控制器的.h头文件中添加以下代码：

@property (nonatomic,strong) NSManagedObjectContext *managedObjectContext;

7.在AppDelegate.m文件中分别#import以上视图控制器的.h文件，并将AppDelegate创建的managedObjectContext的指针传递给以上控制器

如：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

// Override point for customization after application launch.

UITabBarController *tabBarController = (UITabBarController *)self.window.rootViewController;

CurrentLocationViewController *currentLocationViewController = (CurrentLocationViewController *)tabBarController.viewControllers[0];

currentLocationViewController.managedObjectContext = self.managedObjectContext;//传递指针

UINavigationController *navigationController = (UINavigationController *)tabBarController.viewControllers[1];

LocationsViewController *locationsViewController = (LocationsViewController *)navigationController.viewControllers[0];

locationsViewController.managedObjectContext = self.managedObjectContext;//传递指针

MapViewController *mapViewController = (MapViewController *)tabBarController.viewControllers[2];

mapViewController.managedObjectContext = self.managedObjectContext;//传递指针

return YES;

}

当以上视图控制器切换到其他需要应用Core Data操控数据的视图控制器时，可通过prepareForSegue将managedObjectContext的指针传递过去

如：

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender

{

if([segue.identifier isEqualToString:@"TagLocation"])

{

UINavigationController *navigationController = segue.destinationViewController;

LocationDetailsViewController *controller = (LocationDetailsViewController *)navigationController.topViewController;

controller.coordinate = _location.coordinate;

controller.placemark = _placemark;

controller.managedObjectContext = self.managedObjectContext;//传递指针

}

（1）添加数据：

　　Location *location = [NSEntityDescription insertNewObjectForEntityForName:@"Location" inManagedObjectContext:self.managedObjectContext];

　//设置实体的属性　

location.locationDescription = _descriptionText;

location.category = _categoryName;

location.latitude = @(self.coordinate.latitude);

location.longitude = @(self.coordinate.longitude);

location.date = _date;

location.placemark = self.placemark;

NSError *error;

if(![self.managedObjectContext save:&error])

{

//添加处理错误情况的代码

return;

}

（2）修改数据：

　在获取数据【第（4）步】之后，对需要修改的实体的属性修改完之后，调用以下代码

NSError *error;

if(![self.managedObjectContext save:&error])

{

//添加处理错误情况的代码

return;

}

（3）删除数据：

[self.managedObjectContext deleteObject:location];　　//传入需要删除的数据对象（实体）

NSError *error;

if(![self.managedObjectContext save:&error])

{

//添加处理错误情况的代码

return;

}

（4）获取数据：　　　　

　　// 初始化一个查询请求

　　NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

　　// 设置要查询的实体

　　NSEntityDescription *entity = [NSEntityDescription entityForName:@"Location" inManagedObjectContext:self.managedObjectContext]; [fetchRequest setEntity:entity];

　　// 设置排序

　　NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"date" ascending:YES];

　　[fetchRequest setSortDescriptors:@[sortDescriptor]];

　　// 执行请求

　　NSError *error;
　　NSArray *foundObjects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];

　　if (foundObjects == nil) {

　　　　　//添加处理错误情况的代码　　　　

　　　　　return;

　　}

　　_locations = foundObjects; 　　//将获取的数据赋值给实例变量

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