Question

我正在尝试从coredata获取数据。 Coredata在Objective-c中实现。我想获取swift文件中的数据。在项目中，我们同时使用swift和Objective -c。

这是我编写的用于获取swift文件中数据的逻辑。

 let context = appDelegate.persistentContainer.viewContext

let request = NSFetchRequest<NSFetchRequestResult>(entityName: ProjectList_table)
do {
            let result = try context.fetch(request)
            for data in result as! [NSManagedObject] {
               print(data.value(forKey: "username") as! String)
          }

        } catch {

            print("Failed")
        }

我正在尝试使用上面的代码抛出错误。 “ Appdelegate没有成员persistentContainer”

这是我的coredata的Objective-C文件

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

@interface CoreDataController : NSObject

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;

- (void)saveContext;

@end

CoreDataController .m file

#import "CoreDataController.h"

@implementation CoreDataController

@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

- (NSManagedObjectContext *)managedObjectContext
{
    if (_managedObjectContext != nil) {
        return _managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        [_managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return _managedObjectContext;
}

// Returns the managed object model for the application.
// If the model doesn't already exist, it is created from the application's model.
- (NSManagedObjectModel *)managedObjectModel
{
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"expenseDetails" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}

// Returns the persistent store coordinator for the application.
// If the coordinator doesn't already exist, it is created and the application's store added to it.
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (_persistentStoreCoordinator != nil) {
        return _persistentStoreCoordinator;
    }

  //  NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"UserDetails.sqlite"];
    NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    NSURL* storeURL = [NSURL fileURLWithPath:[documentsDirectory stringByAppendingString:@"/expenseDetails.sqlite"] isDirectory:NO];

    NSError *error = nil;
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {

        ////NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return _persistentStoreCoordinator;
}

- (NSURL *)applicationDocumentsDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}


- (void)saveContext
{
    NSError *error = nil;
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil) {
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
            // Replace this implementation with code to handle the error appropriately.
            // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            ////NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }
}



@end

有人可以告诉我如何快速获取数据

Answer 1

这应该可以解决您的问题：-

let context = appDelegate.managedObjectContext

Answer 2

let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext

[https://github.com/Ashutos39/ContactBookDemo][1] if you have the doubt please check this project I have created you can get all fetch, insert to delete from core data concept.

Answer 3

首先，您必须在swift文件中初始化目标类并调用托管对象上下文。

示例：

 let contextRefObj = CoreDataController()

  let context =   contextRefObj.managedObjectContext;

以这种方式尝试，如果您仍然遇到任何问题，请告诉我。

无法快速从coredata获取数据？

3 个答案: