使用核心数据在窗口应用程序中不清楚使用@property [英] unclear use of @property in window app using core data

问题描述

浏览一个用于实验的基于Windows的应用程序ive作为了解核心数据的一种方式，ive注意到该appdelegate具有以下代码

Looking through a Window based application ive used to experiment with as a way of getting my head around core data, ive noticed that the appdelegate has the following code

myAppDelegate .h

myAppDelegate.h

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>

@interface myAppDelegate : NSObject <UIApplicationDelegate> {


NSManagedObjectModel *managedObjectModel;
NSManagedObjectContext *managedObjectContext;       
NSPersistentStoreCoordinator *persistentStoreCoordinator;

UIWindow *window;
UITabBarController *tabBarController;

}

myAppDelegate.m

myAppDelegate.m

#import "myAppDelegate.h"


@interface myAppDelegate (PrivateCoreDataStack)
@property (nonatomic, retain, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;
@end

@implementation myAppDelegate

@synthesize window, tabBarController;

// code ....

// 
- (NSManagedObjectContext *) managedObjectContext {
}
- (NSManagedObjectModel *)managedObjectModel {
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
}

// etc.....

我想了解一些有关该项目正在做什么的事情

i want to understand a few things about what this project is doing

1. 为什么类别声明中的属性？ （如果我删除了privateCoreDataStack类别，那么一切仍然有效...）


2. 为什么属性似乎与实现中的方法链接在一起……managedObjectContext {}等


3. 为什么.h文件中的成员与属性和方法同名


4. 为什么代码补全让我使用点'。'来访问成员，但是然后无法编译，说无法找到吸气剂

1. why the properties in the category declaration? (if i delete the privateCoreDataStack category everything still works...)
2. why the properties appear to be linked with the methods in the implementation ... managedObjectContext {} etc
3. why the members in the .h file have the same name as the properties and the methods
4. why code completion lets me use dot '.' to access the members but then fails on compilation say it cant find a getter

谢谢！

推荐答案

这些是Objective-C的基本概念，但这是一个简短的总结：

These are basic concepts in Objective-C, but here's a quick rundown:

实例成员是通常被认为是私有的，您应该永远不要通过访问器访问其他对象的实例成员。因此，对

Instance members are generally considered to be private, and you should kind of never access the instance members of other objects except through accessors. Hence the need for the

属性声明的需求与方法定义类似； @property（…，只读）NSManagedObjectModel * managedObjectModel; 基本上与-（NSManagedObjectModel *）managedObjectModel; ，除了它启用点标记的事实。

property declarations are like method definitions; @property (…, readonly) NSManagedObjectModel *managedObjectModel; is basically the same as - (NSManagedObjectModel *)managedObjectModel;, except for the fact that it enables dot-notation.

类别用于从目录隐藏这些访问器。类的用户（无论出于何种原因）；因此名称为 PrivateCoreDataStack 。类别是点符号起作用的原因；

The category is used to hide these accessors from the users of the class (for whatever reason); hence the name PrivateCoreDataStack. The category is the reason dot-notation works; if you remove it, it won't.

关于名称；方法名称和实例成员名称位于单独的命名空间中；意味着它们可以具有相同的名称；这非常方便，因为它告诉您-（id）somePropery; 访问 id someProperty; ;或 @属性（非原子，保留）NSManagedObjectContext * managedObjectContext; 访问 NSManagedObjectContext * managedObjectContext 。

As for the names; method names and instance members name live in separate namespaces; meaning that they can have the same name; this is very handy, because it tells you that - (id)somePropery; accesses id someProperty;; or that @property (nonatomic, retain) NSManagedObjectContext *managedObjectContext; accesses NSManagedObjectContext *managedObjectContext.

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