なぜ自分の変数がnilに設定されていますか？

Question

UITableViewControllerでは、didSelectRowAtIndexPathの下に、NSObjectファイルのプロパティを値に設定します。私はNSLogを使用して、変数が実際に設定されていることを確認することができます。しかし、テーブルビューを使用してdidSelectRowAtIndexPathをアクティブにするセルをクリックすると、ビューが別のUITableViewControllerに変更されたときにその変数がnilに設定されていることに気付きました。私はviewDidLoadのNSLogを使ってこのプロパティの値をチェックし、それはnilを返しました。どうしてこれなの？どのようにして自分自身を変えないようにすることができますか？

まずUITableView.m：

#import "enchantmentViewController.h" 
#import "levelViewController.h" 
#import "dataBrain.h" 

@interface enchantmentViewController() 

@property (nonatomic, strong) dataBrain *brain; 
@property (nonatomic, strong) levelViewController *level; 

@end 

@implementation enchantmentViewController 

@synthesize brain = _brain; 
@synthesize level = _level; 

- (dataBrain *)brain 
{ 
    if (!_brain){ 
     _brain = [[dataBrain alloc] init]; 
    } 
    return _brain; 
} 

- (levelViewController *)level 
{ 
    if (!_level){ 
     _level = [[levelViewController alloc] init]; 
    } 
    return _level; 
} 

- (id)initWithStyle:(UITableViewStyle)style 
{ 
    self = [super initWithStyle:style]; 
    if (self) { 
     // Custom initialization 
    } 
    return self; 
} 

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 

    // Uncomment the following line to preserve selection between presentations. 
    // self.clearsSelectionOnViewWillAppear = NO; 

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller. 
    // self.navigationItem.rightBarButtonItem = self.editButtonItem; 
} 

- (void)viewDidUnload 
{ 
    [super viewDidUnload]; 
    // Release any retained subviews of the main view. 
    // e.g. self.myOutlet = nil; 
} 

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation 
{ 
    return (interfaceOrientation == UIInterfaceOrientationPortrait); 
} 

#pragma mark - Table view data source 

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView 
{ 
    //warning Potentially incomplete method implementation. 
    // Return the number of sections. 
    return [self.brain enchantmentNumberOfSections]; 
} 

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section 
{ 
    //#warning Incomplete method implementation. 
    // Return the number of rows in the section. 
    return [self.brain enchantmentNumberOfCells:section]; 
} 

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 

    static NSString *CellIdentifier = @"enchantment"; 
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 

    if (!cell) { 
     cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier]; 
     cell.selectionStyle = UITableViewCellSelectionStyleNone; 
    } 

    cell.textLabel.text = [self.brain enchantmentCellText:indexPath]; 

    return cell; 

} 

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section 
{ 
    return [self.brain enchantmentSectionData:section]; 
} 


/* 
// Override to support conditional editing of the table view. 
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    // Return NO if you do not want the specified item to be editable. 
    return YES; 
} 
*/ 

/* 
// Override to support editing the table view. 
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    if (editingStyle == UITableViewCellEditingStyleDelete) { 
     // Delete the row from the data source 
     [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; 
    } 
    else if (editingStyle == UITableViewCellEditingStyleInsert) { 
     // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view 
    } 
} 
*/ 

/* 
// Override to support rearranging the table view. 
- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath 
{ 
} 
*/ 

/* 
// Override to support conditional rearranging of the table view. 
- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    // Return NO if you do not want the item to be re-orderable. 
    return YES; 
} 
*/ 

#pragma mark - Table view delegate 

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    [tableView deselectRowAtIndexPath:indexPath animated:YES]; 
    [self.brain convertSelectedTableCellToNumberOfPossibleEnchantments:indexPath]; 
    [self.brain test]; 
} 

@end 

第二のUITableViewControllerコード：

#import "levelViewController.h" 
#import "dataBrain.h" 

@interface levelViewController() 

@property (nonatomic, strong) dataBrain *brain; 

@end 

@implementation levelViewController 

@synthesize brain = _brain; 


- (dataBrain *)brain 
{ 
    if (!_brain){ 
     _brain = [[dataBrain alloc] init]; 
    } 
    return _brain; 
} 

- (id)initWithStyle:(UITableViewStyle)style 
{ 
    self = [super initWithStyle:style]; 
    if (self) { 
     // Custom initialization 
    } 
    return self; 
} 

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 

    // Uncomment the following line to preserve selection between presentations. 
    // self.clearsSelectionOnViewWillAppear = NO; 

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller. 
    // self.navigationItem.rightBarButtonItem = self.editButtonItem; 
} 

- (void)viewDidUnload 
{ 
    [super viewDidUnload]; 
    // Release any retained subviews of the main view. 
    // e.g. self.myOutlet = nil; 
} 

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation 
{ 
    return (interfaceOrientation == UIInterfaceOrientationPortrait); 
} 

#pragma mark - Table view data source 

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView 
{ 
    // Return the number of sections. 
    return 1; 
} 

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section 
{ 
    // Return the number of rows in the section. 
    //NSLog(@"needing sections"); 

    NSLog(@"value: %@", [self.brain levelNumberOfCells]); 
    return [self.brain.numberOfLevelsForCurrentEnchantment integerValue]; 
    //[self.brain levelNumberOfCells]; 

} 

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    static NSString *CellIdentifier = @"level"; 
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 

    if (!cell) { 
     cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier]; 
     cell.selectionStyle = UITableViewCellSelectionStyleNone; 
    } 

    cell.textLabel.text = @"jo";//[self.brain levelCellText:indexPath]; 

    return cell; 
} 

@end 

[self.brain test]は、問題のある変数の値を返します。

Answer 1

各viewControllerには独自の脳があり、必要に応じて自動的に割り当てられます。あるVCの脳に変数を設定してVCを切り替えると、今は脳について何かを尋ねるときに、別の脳について尋ねることになります。