将变量保存到代码中的CoreData实体 - Objective-C / XCode [英] Saving a variable to a CoreData entity in code - Objective-C / XCode

问题描述

所以，我有一个非常简单的应用程序，以便学习Obj-C，用户生成一个分数，然后我想将该分数发布到某种用户排行榜。

我的工作
1.生成分数
2.移动到排行榜视图控制器并将分数传递给新的视图控制器
3.将分数添加到临时数组中。

现在，我在CoreData中创建了一个Scores实体，但我从来没有使用CoreData，所以我有点困惑如何使用它。

理想情况下，我想做的不是保存 scoreToBeAddedString 该数组，将它添加到 Scores 实体。

我试图使用此通话，但我遇到了一堆错误。

  CoreDataAppDelegate * appDelegate = 
 [[UIApplication sharedApplication] delegate]; 
 
 NSManagedObjectContext * context = 
 [appDelegate managedObjectContext]; 
 NSManagedObject * newScore; 
 newScore = [NSEntityDescription 
 insertNewObjectForEntityForName：@Scores
 inManagedObjectContext：context]; 
 [newScore setValue：_scoreToBeAddedAsString forKey：@score]; 
 NSError * error; 
 [context save：& error]; 
  

错误：
1. 使用未声明的标识符：'CoreDataAppDelegate
2. 使用未声明的标识符：'appDelegate

我的 LeaderboardViewController.m 文件。

  #importLeaderboardViewController.h 
 
 @interface LeaderboardViewController（）
 
 @end 
 
 @implementation LeaderboardViewController 
 
 {
 NSMutableArray * scores ; 
} 
 
  - （id）initWithNibName：（NSString *）nibNameOrNil bundle：（NSBundle *）nibBundleOrNil 
 {
 self = [super initWithNibName：nibNameOrNil bundle：nibBundleOrNil ]; 
 if（self）{
 //自定义初始化
} 
 return self; 
} 
 
  - （void）viewDidLoad 
 {
 [super viewDidLoad]; 
 
 //将scoreToBeAdded int转换为字符串
 
 NSNumber * anumber = [NSNumber numberWithInteger：_scoreToBeAdded]; 
 
 NSString * scoreToAddAsString = [anumber stringValue]; 
 
 // [scores addObject：scoreToAddAsString]; //这是我在数组中添加分数的地方，但我想摆脱这个解决方案，所以我可以坚持数据。 
 
 // TODO：将scoreToAddAsString添加到CoreData中的Scores实体。 
 
 NSLog（@Leaderboard loaded w new score to add％i，_scoreToBeAdded）; 
} 
 
  - （NSInteger）tableView：（UITableView *）tableView numberOfRowsInSection：（NSInteger）section 
 {
 return [scores count] 
} 
 
 
  - （UITableViewCell *）tableView：（UITableView *）tableView cellForRowAtIndexPath：（NSIndexPath *）indexPath 
 {
 static NSString * simpleTableIdentifier = @SimpleTableCell; 
 
 UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier：simpleTableIdentifier]; 
 
 if（cell == nil）{
 cell = [[UITableViewCell alloc] initWithStyle：UITableViewCellStyleDefault reuseIdentifier：simpleTableIdentifier]; 
} 
 
 cell.textLabel.text = [scores objectAtIndex：indexPath.row]; 
 return cell; 
} 
  

解决方案

添加

>

在您的 LeaderboardViewController.m 文件中添加 #importCoreDataAppDelegate.h $ b

So, I have a very simple app going in order to learn Obj-C, where a user generates a score and then I want to post that score to some sort of "user-leaderboard".

What I have working 1. Generate score 2. Move to a leaderboard view controller and pass score to the new view controller 3. Add the score to a temporary array.

Now, I've created a Scores entity in CoreData, but I've never used CoreData before so I'm a bit confused as to how to use it.

Ideally, what I'd like to do is instead of saving the scoreToBeAddedString to the array, add it to the Scores entity.

I tried to use this call, but I got a bunch of errors.

CoreDataAppDelegate *appDelegate =
    [[UIApplication sharedApplication] delegate];

   NSManagedObjectContext *context =
    [appDelegate managedObjectContext];
   NSManagedObject *newScore;
   newScore = [NSEntityDescription
       insertNewObjectForEntityForName:@"Scores"
       inManagedObjectContext:context];
   [newScore setValue: _scoreToBeAddedAsString forKey:@"score"];
   NSError *error;
   [context save:&error];

Errors: 1. Use of undeclared identifier: 'CoreDataAppDelegate 2. Use of undeclared identifier: 'appDelegate

Here is my LeaderboardViewController.m file.

#import "LeaderboardViewController.h"

@interface LeaderboardViewController ()

@end

@implementation LeaderboardViewController

{
    NSMutableArray *scores;
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    //Convert the scoreToBeAdded int to a string 

    NSNumber *anumber = [NSNumber numberWithInteger:_scoreToBeAdded];

    NSString *scoreToAddAsString = [anumber stringValue];

    //[scores addObject:scoreToAddAsString]; //This is where I was adding the score to the array, but I want to get rid of this solution, so I can persist the data. 

    //TODO: Add the scoreToAddAsString to the "Scores" entity in CoreData. 

    NSLog(@"Leaderboard loaded w new score to add %i", _scoreToBeAdded);
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [scores count];
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *simpleTableIdentifier = @"SimpleTableCell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:simpleTableIdentifier];

    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:simpleTableIdentifier];
    }

    cell.textLabel.text = [scores objectAtIndex:indexPath.row];
    return cell;
}

解决方案

Add #import <CoreData/CoreData.h> in your LeaderboardViewController.h file.

Add #import "CoreDataAppDelegate.h" in your LeaderboardViewController.m file.

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