我想将核心数据添加到现有的 iPhone 项目中，但我仍然遇到很多编译错误:

- NSManagedObjectContext undeclared

 - Expected specifier-qualifier-list before 'NSManagedObjectModel'

 - ...

我已经将核心数据框架添加到目标中(右键单击“目标”下的我的项目，“添加”-“现有框架”，“CoreData.framework”)。

我的头文件:

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

[...]

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

我错过了什么？开始一个新项目不是一种选择......

非常感谢!

编辑 抱歉，我确实有这些实现……但似乎缺少库……实现方法充满编译错误，例如“managedObjectContext undeclared”、“NSPersistentStoreCoordinator undeclared”，还有 NSManagedObjectContext 之前的“Expected ')'”(尽管括号似乎是正确的)...

#pragma mark -
#pragma mark Core Data stack

/**
 Returns the managed object context for the application.
 If the context doesn't already exist, it is created and bound to the persistent store         
coordinator for the application.
 */
- (NSManagedObjectContext *) managedObjectContext {

    if (managedObjectContext != nil) {
        return managedObjectContext;
    }

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


/**
 Returns the managed object model for the application.
 If the model doesn't already exist, it is created by merging all of the models found in    
 application bundle.
 */
- (NSManagedObjectModel *)managedObjectModel {

    if (managedObjectModel != nil) {
        return managedObjectModel;
    }
    managedObjectModel = [[NSManagedObjectModel mergedModelFromBundles:nil] retain];    
    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 = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] 
        stringByAppendingPathComponent: @"Core_Data.sqlite"]];

    NSError *error = nil;
    persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] 
    initWithManagedObjectModel:[self managedObjectModel]];
    if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType 
    configuration:nil URL:storeUrl options:nil error:&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. If it is not possible to recover from the error, display an alert panel that 
    instructs the user to quit the application by pressing the Home button.

     Typical reasons for an error here include:
     * The persistent store is not accessible
     * The schema for the persistent store is incompatible with current managed object 
                model
     Check the error message to determine what the actual problem was.
     */
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}    

return persistentStoreCoordinator;
}

最佳答案

所有 CoreData 头文件都导入到 App_Prefix.pch 中，因此 CoreData 类将在整个项目中可用，因此您不必在需要的文件中手动导入头文件.

因此打开 Xcode 并查找一些文件，如 App_Prefix.pch，默认情况下它位于 Other Sources 组中。在 UIKit 导入语句之后，添加以下行:

#import <CoreData/CoreData.h>

你应该准备好了。

Xcode 4

对于在 Xcode 4 中创建的项目，可以在项目导航器的 Supporting Files 组中找到前缀文件。默认情况下称为“项目名称-Prefix.pch”。

Xcode 6+

从Xcode 6开始，默认不再包含预编译头文件。这是因为引入了模块，take away the need to use precompiled headers.虽然仍然可以手动添加 PCH 文件以全局包含 CoreData header ，但请考虑在每个使用 CoreData 的文件中使用 @import CoreData;* 指定 CoreData 依赖项。这使得依赖关系明确，更重要的是将在未来避免这个问题的问题。

_{* 模块 need to be enabled为了这个工作。}

关于ios - 将核心数据添加到现有的 iPhone 项目，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5959720/