ios - 无法创建 UIManagedDocument

Question

我正在尝试使用 Core Data 制作一个 iPhone 应用程序。我必须使用 NSManagedObjectContext 来访问数据，为此我使用了 UIManagedDocument。但是，如果我尝试使用 UIManagedDocument 创建文档，则文档的 openWithCompletionHandler 不会成功。这就是为什么我的 NSManagedObjectContext 总是 nil 并且 Xcode 说无法在等位置创建文档的原因。以下是类:

AddUserViewController.h

#import <UIKit/UIKit.h>

@interface AddUserViewController : UIViewController

@property (nonatomic, strong) NSManagedObjectContext *managedObjectContext;
@property (nonatomic,strong) UIManagedDocument *document;

@end

AddUserViewController.m

#import "AddUserViewController.h"
#import "User.h"
#import "User+Create.h"

@interface AddUserViewController ()
@property (weak, nonatomic) IBOutlet UITextField *nameField;
@property (weak, nonatomic) IBOutlet UITextField *ageField;
@property (weak, nonatomic) IBOutlet UITextField *sexField;
@property (weak, nonatomic) IBOutlet UITextField *weightField;
@property (weak, nonatomic) IBOutlet UITextField *activityField;


@end

@implementation AddUserViewController

-(void)setManagedObjectContext:(NSManagedObjectContext *)managedObjectContext{
        _managedObjectContext = managedObjectContext;
}



-(void)createOrWriteDocument{
    NSURL *url = [[[NSFileManager defaultManager]URLsForDirectory:NSDocumentationDirectory inDomains:NSUserDomainMask]firstObject];
    url = [url URLByAppendingPathComponent:@"Activities"]; // edited mistakenly deleted
    self.document = [[UIManagedDocument alloc] initWithFileURL:url];

    if ([[NSFileManager defaultManager] fileExistsAtPath:[url path]]) {
        [self.document openWithCompletionHandler:^(BOOL success) {
            if (success) [self documentIsReady];
            if (!success){
                NSLog(@"could not open document at %@",url);
            }

        }];


    } else {
        [self.document saveToURL:url
           forSaveOperation:UIDocumentSaveForCreating
          completionHandler:^(BOOL success) {
              if (success) {
                  [self documentIsReady];
              }
              if (!success){
                  NSLog(@"could not create document at %@",url);
              }
          }];
    }

}


- (void)documentIsReady
{
    if (self.document.documentState == UIDocumentStateNormal) {
        self.managedObjectContext = self.document.managedObjectContext; 
    } }

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    if (!self.managedObjectContext) {
        [self createOrWriteDocument];
    }

    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc]
                                   initWithTarget:self
                                   action:@selector(dismissKeyboard)];

    [self.view addGestureRecognizer:tap];
}

-(void)dismissKeyboard{
    [self.nameField resignFirstResponder];
    [self.ageField resignFirstResponder];
    [self.sexField resignFirstResponder];
    [self.weightField resignFirstResponder];
    [self.activityField resignFirstResponder];
}

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{

    if ([segue.identifier isEqualToString:@"setUser:"]) {

        //User *user = [[User alloc]init];
        User *user = [User createUserWithname:self.nameField.text
                                      withAge:[NSNumber numberWithDouble:[self.ageField.text doubleValue]]
                                      withSex:self.sexField.text
                                   withWeight:[NSNumber numberWithDouble:[self.weightField.text doubleValue]]
                                 withActivity:self.activityField.text
                       inManagedObjectContext:self.managedObjectContext];

        if ([segue.destinationViewController respondsToSelector:@selector(setUser:)]) {
            [segue.destinationViewController performSelector:@selector(setUser:) withObject:user];

        }
    }

}

@end

编辑

我解决了这个问题。问题出在 NSURL *url = [[[NSFileManager defaultManager]URLsForDirectory:NSDocumentationDirectory inDomains:NSUserDomainMask]firstObject];线。我使用 NSDocumentDirectory 而不是 NSDocumentationDirectory，它解决了问题。

Answer 1

您可以尝试使用此代码来创建您的 managedobjectcontext。

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

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