按下按鈕後，數據（char *）在登錄後出現損壞

我對iphone編程很新手。問題是當我按下按鈕時，數據將被銷燬。我找不到我的代碼錯在哪裏以及爲什麼。請幫幫我。按下按鈕後，數據（char *）在登錄後出現損壞

這是我的程序概述。

1. load text data from "sample.txt" 
2. log the data 
3. When I push a button, it logs the data again.

AppDelegate.h

#import <UIKit/UIKit.h> 

@interface AppDelegate : UIResponder <UIApplicationDelegate> 

@property (strong, nonatomic) UIWindow *window; 
@property (strong, nonatomic) UIButton *myButton1; 
@property (assign) unsigned char* bytePtr; 

@end

AppDelegate.m：

~snip~ 

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; 
    // Override point for customization after application launch. 
    self.window.backgroundColor = [UIColor whiteColor]; 
    [self.window makeKeyAndVisible]; 

    self.myButton1 = [UIButton buttonWithType:UIButtonTypeRoundedRect]; 
    [self.myButton1 setFrame:CGRectMake(0, 0, 100 ,100)]; 
    [self.myButton1 addTarget:self action:@selector(button1DidPushed) forControlEvents:UIControlEventTouchUpInside]; 
    [self.myButton1 setTitle:@"push" forState:UIControlStateNormal]; 

    [self.window addSubview:self.myButton1]; 
    [self load]; 

    return YES; 
} 


- (void) load 
{ 
    NSString* path = [[NSBundle mainBundle] pathForResource:@"sample" ofType:@"txt"]; 
    NSData* data = [NSData dataWithContentsOfFile:path]; 
    self.bytePtr = (unsigned char *)[data bytes]; 
    NSLog(@"%s", self.bytePtr); 
} 


- (void)button1DidPushed 
{ 
    UIAlertView *alerView = [[UIAlertView alloc] initWithTitle:@"Enter something..." message:@"" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK", nil]; 
    alerView.alertViewStyle = UIAlertViewStylePlainTextInput; 
    [alerView show]; 
} 

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex 
{ 
    NSString *title = [alertView buttonTitleAtIndex:buttonIndex]; 
    if([title isEqualToString:@"OK"]) 
    { 

    } 
    NSLog(@"%s", self.bytePtr); 
} 

~snip~

sample.txt的：

abcdefghijklmnopqrstuvwxyz

輸出：

abcdefghijklmnopqrstuvwxyz 
<----- When I push the button the mark similar to "?" will appear on output window.(I couldn't show it here(It's probabily ascii code 2(STX))) That is why I think the data is destroyed.

環境：

xcode 6.0.1

感謝。

來源

2014-09-28 Kei Minagawa

如果你希望你的'bytePtr'存儲數據，它不會。當數據超出範圍時，該指針的值將毫無意義。你應該閱讀關於指針/通用C編程。 – sapi 2014-09-28 06:38:37

的問題是，你是不是保留NSData對象：

- (void) load 
{ 
    NSString* path = [[NSBundle mainBundle] pathForResource:@"sample" ofType:@"txt"]; 
    NSData* data = [NSData dataWithContentsOfFile:path]; // here 
    self.bytePtr = (unsigned char *)[data bytes]; 
    NSLog(@"%s", self.bytePtr); 
}

一旦方法返回NSData對象將被銷燬，因此緩衝指向self.bytePtr不再有效。

要解決此問題，請將self.bytePtr更改爲NSData對象並將其存儲。

來源

2014-09-28 08:44:50 Droppy

啊我明白了。謝謝。 – 2014-09-28 09:09:56

@keimina忘了提及，如果這些數據是由字符組成的，你應該使用'NSString'而不是'NSData'。因此，使用所需的編碼將'NSData'轉換爲'NSString'，並將其存儲起來。 – Droppy 2014-09-28 09:11:48

首先，爲了接收您的alertView:clickedButtonAtIndex:方法調用，您需要將您的UIAlertView代理設置爲self。

[alertView setDelegate:self] // make sure you set UIAlertViewDelegate protocol on the method owner

否則應該使用使用initWithData:encoding:的NSString對象初始化。

來源

2014-09-28 08:39:46 believesInSanta

按下按鈕後，數據（char *）在登錄後出現損壞

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