CoreData与Objective-C跨平台开发指南

# Core Data与Objective-C跨平台开发指南 ## 1. Core Data的使用 ### 1.1 创建NSManagedObject子类 要使用Core Data，首先需要创建NSManagedObject子类。具体操作步骤如下： 1. 保持所有实体处于选中状态，依次点击“File” > “New” > “File”。 2. 在弹出的窗口中，选择“iOS” > “Core Data” > “NSManagedObject subclass”。 3. 点击“Next”，然后点击“Create”。此时会弹出一个警告对话框，提示你即将覆盖之前的Project类文件，由于确实需要更新该文件，所以点击“Replace”。 完成上述操作后，就可以在不破坏应用程序的情况下使用Core Data了。 ### 1.2 代码示例 以下是一系列相关代码示例： #### 1.2.1 AppDelegate.h ```objective-c #import <UIKit/UIKit.h> #import "AppModel.h" @interface AppDelegate : UIResponder <UIApplicationDelegate> @property (strong, nonatomic) UIWindow *window; @end ``` #### 1.2.2 AppDelegate.m ```objective-c #import "AppDelegate.h" @implementation AppDelegate @synthesize window = _window; - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{ //Create a new AppModel instance AppModel *dataModel = [[AppModel alloc] init]; //Make a project Project *pl = [dataModel makeNewProject]; pl.name = @"Projl"; //Make a task Task *t1 = (Task *)[NSEntityDescription insertNewObjectForEntityForName:@"Task" inManagedObjectContext:[dataModel managedObjectContext]]; t1.name = @"Task 1"; t1.details = @"Task details"; t1.dueDate = [NSDate date]; t1.priority = [NSNumber numberWithInt:1]; //Assign a worker to this task: Worker *managedWorker = (Worker *)[NSEntityDescription insertNewObjectForEntityForName:@"Worker" inManagedObjectContext:[dataModel managedObjectContext]]; managedWorker.name = @"John"; managedWorker.Role = @"Programmer"; t1.assignedTo = managedWorker; //Add the task to the project [pl addListOfTasksObject:t1]; //Make a task Task *t2 = (Task *)[NSEntityDescription insertNewObjectForEntityForName:@"Task" inManagedObjectContext:[dataModel managedObjectContext]]; t2.name = @"Task 2"; t2.details = @"Task details"; t2.dueDate = [NSDate date]; t2.priority = [NSNumber numberWithInt:1]; //Add the task to the project [pl addListOfTasksObject:t2]; //Get all the projects in the data store NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Project" inManagedObjectContext:[dataModel managedObjectContext]]; request.entity = entity; NSArray *listOfProjects = [[dataModel managedObjectContext] executeFetchRequest:request error:nil]; //print out contents of all the projects (including the tasks): NSLog(@"-----"); NSLog(@"NEW PROJECTS IN CONTEXT"); [listOfProjects enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) { NSLog(@"project.name = %@", [obj name]); [[obj listOfTasks] enumerateObjectsUsingBlock:^(id obj, BOOL *stop) { NSLog(@" task.name = %@", [obj name]); NSLog(@" task.assignedTo = %@", [[obj assignedTo] name]); }]; }]; self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; self.window.backgroundColor = [UIColor whiteColor]; [self.window makeKeyAndVisible]; return YES; } @end ``` #### 1.2.3 AppModel.h ```objective-c #import <Foundation/Foundation.h> #import <CoreData/CoreData.h> #import "Project.h" #import "Worker.h" #import "Task.h" @interface AppModel : NSObject -(NSURL *)dataStoreURL; @property (nonatomic, strong, readonly) NSManagedObjectModel *managedObjectModel; @property (nonatomic, strong, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator; @property (nonatomic, strong, readonly) NSManagedObjectContext *managedObjectContext; -(Project *)makeNewProject; -(Worker *)makeNewWorker; -(Task *)makeNewTask; @end ``` #### 1.2.4 AppModel.m ```objective-c #import "AppModel.h" @implementation AppModel NSManagedObjectModel *_managedObjectModel; NSPersistentStoreCoordinator *_persistentStoreCoordinator; NSManagedObjectContext *_managedObjectContext; -(Project *)makeNewProject{ Project *managedProject = (Project *)[NSEntityDescription insertNewObjectForEntityForName:@"Project" inManagedObjectContext:[self managedObjectContext]]; managedProject.name = @"New Project"; managedProject.descrip = @"This is a new project"; managedProject.dueDate = [NSDate date]; managedProject.personInCharge = [self makeNewWorker]; return managedProject; } -(Worker *)makeNewWorker{ Worker *managedWorke ```