對象分配和初始化后，對象指針設置為null

Question

我有一個自定義對象類（Ship.h和Ship.m），並且我正在嘗試使用以下代碼創建一個新的Ship類型對象：

Ship *PlayerShip = [[Ship alloc] init];

該代碼當前在我的First view controller.m中

- (void)viewDidLoad{

但是我已經嘗試過了

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil

也一樣

我創建了PlayerShip對象，沒有任何問題，然后用

NSLog(@"Player ship: %@",PlayerShip);

它的日志也很好。

然后在代碼的另一部分（我放置它的地方以外的地方），例如NSTimer，我嘗試使用相同的NSLog行並返回

玩家飛船：空

是否出於某種原因刪除了PlayerShip對象？

我將不勝感激任何幫助。

以下是我的shipViewController.h

#import <UIKit/UIKit.h>
#import "Ship.h"
@interface ShipViewController : UIViewController{
IBOutlet UILabel *PlayerShipLabel;
IBOutlet UIProgressView *PlayerHullBar;
IBOutlet UIProgressView *PlayerShieldBar;
IBOutlet UILabel *PlayerCreditsLabel;
IBOutlet UIImageView *PlayerShipImage;
IBOutlet UIButton *PlayerRepairBreachButton;
}


@end
Ship *PlayerShip;

這是ShipViewController.m

#import "ShipViewController.h"

@interface ShipViewController ()

@end

@implementation ShipViewController

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

    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    Ship *PlayerShip = [[Ship alloc] init];
    NSLog(@"Player ship: %@",PlayerShip);
}



- (IBAction)ShieldSwitch:(id)sender {
    NSLog(@"Ship is %@ ",PlayerShip);

}

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

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

@end

這是應用程序首次啟動時程序的輸出：

2014-06-12 19:02:27.503 First Game[5193:60b] Created a new ship!
2014-06-12 19:02:27.504 First Game[5193:60b] Player ship: <Ship: 0x8c30f70>

這是我按下按鈕驗證PlayerShip時的輸出：

2014-06-12 19:02:29.472 First Game[5193:60b] Ship is (null) 

Answer 1

有幾個問題。

1. 為什么要聲明Ship *PlayerShip; 在@end語句后的.h文件中？ 這使其成為全局變量。 使其與其他實例變量一樣，但將其放在@interface語句的花括號中。
2. 在viewDidLoad您將創建一個與（即將成為）實例變量同名的局部變量。 不要聲明新變量。 只需將新對象分配給實例實例變量。