iOS：核心数据保存和搜索NSEntityDescription或SetAttr描述

Question

我是Objective-C和CoreData的新手，想要学习它并尝试使用Xcode 5，我试着制作这个tutorial。

我已经跟着一些其他的CoreData表名，但是我的“ViewController.m”出现了一些错误，并且不知道要改变什么，我可以看到它建议将“NSEntityDescription”更改为“kSetAttrDescription”但不知道如果那是对还是错，希望有人可以告诉我该做什么 - 所以我下次就知道了。

错误问题

错误说明

我的ViewController.m代码。

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

//Save data as CoreData, to CoreData Table "Kunder" field "navn", "adresse", "alder" from textfield _name.text, _adress.text, _age.text.
- (IBAction)saveData:(id)sender {
    AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

    NSManagedObjectContext *context = [appDelegate managedObjectContext];
    NSManagedObject *newContact;
    newContact = [NSEntityDescription insertNewObjectForEntityForName:@"Kunder" inManagedObjectContext:context];
    [newContact setValue: _name.text forKey:@"navn"];
    [newContact setValue: _adress.text forKey:@"adresse"];
    [newContact setValue: _age.text forKey:@"alder"];
    //if textfield empty, then error else save and show label message "Kunde Gemt".
    _name.text = @"";
    _adress.text = @"";
    _age.text = @"";
    NSError *error;
    [context save:&error];
    _status.text = @"Kunde Gemt";
}

//Find-search for user by name.
- (IBAction)findKunde:(id)sender {
    AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

    NSManagedObjectContext *context = [appDelegate managedObjectContext];

    NSEntityDescription *entityDesc = [NSEntityDescription entityForName:@"Kunder" inManagedObjectContext:context];

    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    [request setEntity:entityDesc];

    NSPredicate *pred =
    [NSPredicate predicateWithFormat:@"(navn = %@)", _name.text];
    [request setPredicate:pred];
    NSManagedObject *matches = nil;
    //if no user then error, else take name match and get "adresse" and "alder" from CoreData and show it in the text fields _adress.text and _age.text and show matche count in status label.
    NSError *error;
    NSArray *objects = [context executeFetchRequest:request error:&error];

    if ([objects count] == 0) {
        _status.text = @"Ingen fundet";
    } else {
        matches = objects[0];
        _adress.text = [matches valueForKey:@"adresse"];
        _age.text = [matches valueForKey:@"alder"];
        _status.text = [NSString stringWithFormat: @"%lu antal fundet", (unsigned long)[objects count]];
    }
}
@end

我的ViewController.h页面（无错误）

#import <UIKit/UIKit.h>
#import "AppDelegate.h" 

@interface ViewController : UIViewController
@property (strong, nonatomic) IBOutlet UITextField *name;
@property (strong, nonatomic) IBOutlet UITextField *adress;
@property (strong, nonatomic) IBOutlet UITextField *age;
@property (strong, nonatomic) IBOutlet UILabel *status;
- (IBAction)saveData:(id)sender;
- (IBAction)findKunde:(id)sender;

@end

我的AppDelegate.m文件

#import "AppDelegate.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    return YES;
}
....
@end

更新

在字段中添加文本并点击保存时，我会收到一条“保存确定”消息，它会跳转到xcode并显示给我。

Answer 1

您好像忘了导入<CoreData/CoreData.h>。 您可以将导入添加到预编译头（...- Prefix.pch）文件中 看起来与此类似：

#import <Availability.h>

#ifndef __IPHONE_5_0
#warning "This project uses features only available in iOS SDK 5.0 and later."
#endif

#ifdef __OBJC__
    #import <UIKit/UIKit.h>
    #import <Foundation/Foundation.h>
    #import <CoreData/CoreData.h>         // <-- Add this !!
#endif

您可能还需要添加＆＃34; CoreData.framework＆＃34;和＃34; Link Binary With Libraries＆＃34; 目标部分＆＃34;构建阶段＆＃34;。