为什么 NSString 变空（没有原因）？

发布于 2024-11-30 17:11:32 字数 969 浏览 2 评论 0原文

我对 Objective C 很着迷。请看下面的代码。

FirstViewController.h：

@interface FirstViewController : UIViewController {
    IBOutlet UITextView *textView;
    IBOutlet UIBarButtonItem *button;
    NSString* superString;
}

- (IBAction)buttonDown;

FirstViewController.m：

- (void)viewDidLoad {
    [super viewDidLoad];
    superString = [NSString stringWithFormat:"%@", @"A_super_string_file.txt"];
    [self buttonDown];
}

- (IBAction)buttonDown {
    NSError* err = nil;
    NSString* text = [NSString stringWithContentsOfFile:superString encoding:NSUTF8StringEncoding error:&err];
    [textView setText:text];
}

运行应用程序。 A_super_string_file.txt 成功显示在textView中。
按下按钮。应用程序崩溃是因为 superString 引用了与步骤 1 中相同的地址，但该地址上有另一个变量或没有任何变量。 superString 上的打印说明不显示任何内容或随机其他变量（甚至可能是不同类型）。

会发生什么？我是一名技能开发人员，但对这种情况一无所知。非常感谢您的帮助！

更新：可能，它在工作中隐藏了自动释放。但是什么时候释放内存呢？每次都在不同的时刻还是在某个特定的时刻？

原文

I am going crazy with Objective C. Please look to the following code.

FirstViewController.h:

@interface FirstViewController : UIViewController {
    IBOutlet UITextView *textView;
    IBOutlet UIBarButtonItem *button;
    NSString* superString;
}

- (IBAction)buttonDown;

FirstViewController.m:

- (void)viewDidLoad {
    [super viewDidLoad];
    superString = [NSString stringWithFormat:"%@", @"A_super_string_file.txt"];
    [self buttonDown];
}

- (IBAction)buttonDown {
    NSError* err = nil;
    NSString* text = [NSString stringWithContentsOfFile:superString encoding:NSUTF8StringEncoding error:&err];
    [textView setText:text];
}

Run the application. A_super_string_file.txt successfully displayed in textView.
Press the button. The application crashes because superString refers on the same address as in the step 1 but there is another variable or nothing on this address. Print Description on superString displays nothing or random other variable (may be even different type).

What happens? I am a skill developer but have no idea in this case. Thanks a lot for help!

UPDATE: Possibly, it's hidden autorelease in the work. But when it releases memory? On different moment every time or on some exact moment?

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我们只是彼此的过ke 2024-12-07 17:11:32

NSString 的 +stringWithFormat: 是自动释放的。如果您希望它保留下来，您需要保留它。

属性是实现此目的的好方法，因为它减少了您需要担心的内存管理量。

.h.m

@interface FirstViewController : UIViewController {
    IBOutlet UITextView *textView;
    IBOutlet UIBarButtonItem *button;
    NSString* superString;
}

@property (nonatomic, copy) NSString* superString;

- (IBAction)buttonDown;

@synthesize superString

- (void)viewDidLoad {
    [super viewDidLoad];
    [self setSuperString:[NSString stringWithFormat:"%@", @"A_super_string_file.txt"]];
    [self buttonDown];
}

- (IBAction)buttonDown {
    NSError* err = nil;
    NSString* text = [NSString stringWithContentsOfFile:superString encoding:NSUTF8StringEncoding error:&err];
    [textView setText:text];
}

- (void)dealloc {
    [superString release];
    [super dealloc];
}

NSString's +stringWithFormat: is autoreleasing. You need to retain it if you want it to stay around.

Properties are a good way to do this, because it cuts down how much memory management you need to worry about yourself.

@interface FirstViewController : UIViewController {
    IBOutlet UITextView *textView;
    IBOutlet UIBarButtonItem *button;
    NSString* superString;
}

@property (nonatomic, copy) NSString* superString;

- (IBAction)buttonDown;

@synthesize superString

- (void)viewDidLoad {
    [super viewDidLoad];
    [self setSuperString:[NSString stringWithFormat:"%@", @"A_super_string_file.txt"]];
    [self buttonDown];
}

- (IBAction)buttonDown {
    NSError* err = nil;
    NSString* text = [NSString stringWithContentsOfFile:superString encoding:NSUTF8StringEncoding error:&err];
    [textView setText:text];
}

- (void)dealloc {
    [superString release];
    [super dealloc];
}

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