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Stanislav K.
Asked:2020-02-17 04:43:06 +0800 CST2020-02-17 04:43:06 +0800 CST

CoreData 堆栈初始化

  • 772

我根据 Apple 网站的说明在 CoreData Stack 应用程序中进行了操作：

@interface MyDataController : NSObject

@property (strong, nonatomic, readonly) NSPersistentContainer *persistentContainer;

- (id)initWithCompletionBlock:(CallbackBlock)callback;

@end

@implementation MyDataController

- (id)init
{
    self = [super init];
    if (!self) return nil;

    self.persistentContainer = [[NSPersistentContainer alloc] initWithName:@"DataModel"];
    [self.persistentContainer loadPersistentStoresWithCompletionHandler:^(NSPersistentStoreDescription *description, NSError *error) {
        if (error != nil) {
            NSLog(@"Failed to load Core Data stack: %@", error);
            abort();
        }
        callback();
    }];

    return self;
}

遇到了问题，persistentContainer有属性readonly，并且在

self.persistentContainer = [[NSPersistentContainer alloc] initWithName:@"DataModel"];

不允许自己被覆盖，怎么办？

我正确理解@interface.h 文件和@implementation.m 中的内容？

objective-c

1 个回答

  1. Best Answer

    为了初始化一个只读属性，你必须直接访问你的属性所代表的变量：

    _persistentContainer = [[NSPersistentContainer alloc] initWithName:@"DataModel"];
[_persistentContainer loadPersistentStoresWithCompletionHandler:^(NSPersistentStoreDescription *description, NSError *error) {
    if (error != nil) {
        NSLog(@"Failed to load Core Data stack: %@", error);
        abort();
    }
    callback();
}];

    现在关于将代码划分为接口和实现。我将制作以下带有扩展名“*.h”的头文件（我还为您的 CallbackBlock 回调函数的类型添加了同义词）：

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

typedef void(^CallbackBlock)(void);

@interface MyDataController : NSObject

@property (strong, nonatomic, readonly) NSPersistentContainer *persistentContainer;

- (id)initWithCompletionBlock:(CallbackBlock)callback;

@end

    我会像这样实现（换句话说，文件的内容带有“*.m”扩展名）：

    #import "MyDataController.h"

@implementation MyDataController

- (id)initWithCompletionBlock:(CallbackBlock)callback;
{
    self = [super init];
    if (!self) return nil;

    _persistentContainer = [[NSPersistentContainer alloc] initWithName:@"DataModel"];
    [_persistentContainer loadPersistentStoresWithCompletionHandler:^(NSPersistentStoreDescription *description, NSError *error) {
        if (error != nil) {
            NSLog(@"Failed to load Core Data stack: %@", error);
            abort();
        }
        callback();
    }];

    return self;
}

@end
    • 0

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