在具有强引用的另一个对象 ( dataControllerin )的属性上设置的数组的键变为. 我不明白为什么。BWMasterViewControllernull
BWMasterViewController
标题：
#import <UIKit/UIKit.h>
@class BWBirdSightingDataController;
@interface BWMasterViewController : UITableViewController
@end
执行：
#import "BWMasterViewController.h"
#import "BWBirdSightingDataController.h"
#import "Bird.h"
#import "BWWebviewController.h"
@interface BWMasterViewController()
@property (strong, nonatomic) BWBirdSightingDataController *dataController;
@property (copy, nonatomic) NSString *test;
@end
@implementation BWMasterViewController
- (void)awakeFromNib
{
[super awakeFromNib];
NSLog(@"awake from nib");
self.dataController = [[BWBirdSightingDataController alloc] init];
self.test = @"Test var";
NSLog(@"test: %@", self.test);
Bird *bird = [self.dataController objectInListAtIndex:0];
NSLog(@"bird object: %@", bird);
NSLog(@"bird name: %@", bird.name)
}
- (void)viewDidLoad
{
[super viewDidLoad];
NSLog(@"view did load");
NSLog(@"test: %@", self.test);
Bird *bird = [self.dataController objectInListAtIndex:0];
NSLog(@"bird object: %@", bird);
NSLog(@"bird name: %@", bird.name)
}
// ....
BWBirdSightingDataController
标题：
#import <Foundation/Foundation.h>
@class Bird;
@interface BWBirdSightingDataController : NSObject
- (NSUInteger)countOfList;
- (Bird *)objectInListAtIndex:(NSUInteger)theIndex;
@end
执行：
#import "BWBirdSightingDataController.h"
#import "BWDataController.h"
#import "Bird.h"
@interface BWBirdSightingDataController ()
-(void)initializeDefaultDataList;
@property (nonatomic, copy) NSMutableArray *birds;
@end
@implementation BWBirdSightingDataController
- (id)init
{
if (self = [super init]) {
[self initializeDefaultDataList];
return self;
}
return nil;
}
- (void)initializeDefaultDataList
{
BWDataController *dataController = [[BWDataController alloc] init];
NSEntityDescription *birdsEntity = [NSEntityDescription
entityForName:@"Bird"
inManagedObjectContext:dataController.managedObjectContext];
NSFetchRequest *fetchBirds = [[NSFetchRequest alloc] init];
[fetchBirds setEntity:birdsEntity];
NSError *fetchError = nil;
NSArray *birdsObjects = [dataController.managedObjectContext
executeFetchRequest:fetchBirds
error:&fetchError];
self.birds = [birdsObjects mutableCopy];
}
- (NSUInteger)countOfList
{
return [self.birds count];
}
- (Bird *)objectInListAtIndex:(NSUInteger)theIndex
{
return self.birds[theIndex];
}
@end
鸟
Bird 是一个NSManagedObject基于 CoreData 的实体。
标题：
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
@interface Bird : NSManagedObject
@property (nonatomic, retain) NSDate * date;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSString * location;
@property (nonatomic, retain) NSString * image;
@property (nonatomic, retain) NSString * url;
@end
执行：
#import "Bird.h"
@implementation Bird
@dynamic date;
@dynamic name;
@dynamic location;
@dynamic image;
@dynamic url;
@end
输出
当我运行它时，它会输出：
2013-05-31 11:36:47.824 BirdWatching[69565:c07] awake from nib
2013-05-31 11:36:47.834 BirdWatching[69565:c07] test: Test var
2013-05-31 11:36:47.834 BirdWatching[69565:c07] bird object: <Bird: 0x8545ec0> (entity: Bird; id: 0x8545040 <x-coredata://D24A664F-8E8F-4AF0-891C-098C8A7DD860/Bird/p1> ; data: <fault>)
2013-05-31 11:36:47.835 BirdWatching[69565:c07] bird name: Pigeon
2013-05-31 11:36:47.839 BirdWatching[69565:c07] view did load
2013-05-31 11:36:47.840 BirdWatching[69565:c07] test: Test var
2013-05-31 11:36:47.840 BirdWatching[69565:c07] bird object: <Bird: 0x8545ec0> (entity: Bird; id: 0x8545040 <x-coredata://D24A664F-8E8F-4AF0-891C-098C8A7DD860/Bird/p1> ; data: <fault>)
2013-05-31 11:36:47.840 BirdWatching[69565:c07] bird name: (null)
如您所见，在viewDidLoad函数中，bird.name 已变为空。怎么会？我将该属性声明为强参考。
当我定义self.dataControllerin时，我遇到了同样的问题viewDidLoad，那么它将为 null in prepareForSegue，我也需要它。