CODEWITHSUNDEEP
iosobjective-cdesign-patternspersistencerealm
ctb1991
ctb1991

Reputation: 21

How to keep a reference to a single, persisted Realm object

I understand the general concept of how auto-updating results and realm notifications can be used to update my UI. I am trying to wrap my head around the best approach for doing the same for cases where my view controller only every has a single realm object (An example might be a chat controller that has a RLMResults or RLMArray of messages, but only a single "conversation" object).

I have been able to come up with the two approaches below, but neither seems right. What would be the correct way to implement this?

Approach A:

@interface ViewController ()

@property(nonatomic, assign) NSInteger objectPrimaryKey;
@property(nonatomic, retain) MyRealmObject *realmObject;

@end

@implementation ViewController

- (void)viewDidLoad
{
  [super viewDidLoad];

  self.objectPrimaryKey = 123;
  self.realmObject = [MyDataManager 
                            realmObjectWithID:self.objectPrimaryKey];

  // Set realm notification block
  __weak typeof(self) weakSelf = self;
  self.notification = [[MyDataManager realm] 
                        addNotificationBlock:^(NSString *note, 
                                               RLMRealm *realm) {
    [weakSelf reloadData];
  }];
  [self reloadData];
}

- (void)reloadData {
  if(self.realmObject.isInvalidated) {
    self.realmObject = [MyDataManager 
                            realmObjectWithID:self.objectPrimaryKey];
  }
  // Populate the UI with self.realmObject
}

@end

Approach B:

@interface ViewController ()

@property(nonatomic, assign) NSInteger objectPrimaryKey;
@property(nonatomic, retain) RLMResults *realmObjectResults;
@property(nonatomic, readonly) MyRealmObject *realmObject;

@end

@implementation ViewController

- (void)viewDidLoad
{
  [super viewDidLoad];

  self.objectPrimaryKey = 123;
  self.realmObjectResults = [MyDataManager
                             realmObjectResultsWithID:self.objectPrimaryKey];

  // Set realm notification block
  __weak typeof(self) weakSelf = self;
  self.notification = [[MyDataManager realm]
                       addNotificationBlock:^(NSString *note, 
                                              RLMRealm *realm) {
    [weakSelf reloadData];
  }];
  [self reloadData];
}

- (void)reloadData {
  // Populate the UI with self.realmObject.
  // Don't think we need to check isInvalid here?
}

- (MyRealmObject *)realmObject {
  return self.realmObjectResults.firstObject;
}

@end

Upvotes: 2

Views: 413

Answers (1)

jpsim
jpsim

Reputation: 14409

Approach "A" is correct, although the only time your object would be invalidated is if you've deleted it, at which point re-obtaining it via realmObjectWithID: won't make a difference (assuming this is some wrapper around +[RLMObject objectForPrimaryKey:])

@interface ViewController ()

@property(nonatomic, assign) NSInteger objectPrimaryKey;
@property(nonatomic, retain) MyRealmObject *realmObject;

@end

@implementation ViewController

- (void)viewDidLoad
{
  [super viewDidLoad];

  self.objectPrimaryKey = 123;
  self.realmObject = [MyDataManager 
                            realmObjectWithID:self.objectPrimaryKey];

  // Set realm notification block
  __weak typeof(self) weakSelf = self;
  self.notification = [[MyDataManager realm] 
                        addNotificationBlock:^(NSString *note, 
                                               RLMRealm *realm) {
    [weakSelf updateUI];
  }];
  [self updateUI];
}

- (void)updateUI {
  // Populate the UI with self.realmObject
}

@end

Upvotes: 1

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