NSUserDefaults不加載我想要的數字

Question

我想在應用程序關閉後使用NSUserDefaults保存兩個變量。一個是第一個引導和另一個顯示。準備不好的代碼 -

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 

    NSUserDefaults *defaults1 = [NSUserDefaults standardUserDefaults]; //Here is where it is supposed to be loading the firstBoot variable to check whether or not it is the first boot 
    NSInteger boot = [defaults1 integerForKey:@"firstBoot"]; 
    firstBoot = boot; //Sort of pointless variable swapping 

    if (firstBoot == 0) //Detects if isn't first boot, checks whether or not showAgain is yes or no (1=yes, 0=no) 
    { 
     NSUserDefaults *defaults1 = [NSUserDefaults standardUserDefaults]; 
     NSInteger boot = [defaults1 integerForKey:@"firstBoot"]; 
     NSUserDefaults *defaults2 = [NSUserDefaults standardUserDefaults]; 
     NSInteger show = [defaults2 integerForKey:@"showAgain"]; 
     firstBoot = boot; //More var swapping 
     showAgain = show; //^^ 
    } 
    else 
    { 
     firstBoot = 1; //If it is the first boot, or the variable wasn't 0, it sets them both to 1. 
     showAgain = 1; 
    } 
    if ((firstBoot == 1) || (showAgain == 1)) //Checks if its the firstBoot or showAgain is set to yes 
    { 
     UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Check the 'About' tab for help!" //Displays alert 
               message:@"" 
               delegate:self 
             cancelButtonTitle:@"Don't show again" 
             otherButtonTitles:@"OK", nil]; 
     [alert show]; 
    } 
    else 
    { 
     UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"firstboot and showagain != 1" //Displays alert if it isn't the first boot, or isn't 1 and showAgain isn't set to yes(1). 
                message:@"" 
                delegate:self 
              cancelButtonTitle:@"wrong" 
              otherButtonTitles:@"OK", nil]; 
     [alert show]; 
    } 
} 

Alert-

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex { 
    if (buttonIndex == [alertView cancelButtonIndex]) 
    { 
     showAgain = 0; //If user clicks "Don't show again", set showAgain to off(0) and tell it it isn't the first boot anymore 
     firstBoot = 0; 

     NSUserDefaults *defaults1 = [NSUserDefaults standardUserDefaults]; 
     [defaults1 setInteger:0 forKey:@"firstBoot"]; //Hopefully stores firstBoot as 0 
     [defaults1 synchronize]; 

     NSUserDefaults *defaults2 = [NSUserDefaults standardUserDefaults]; 
     [defaults2 setInteger:0 forKey:@"showAgain"]; //Again storing showAgain as 0 
     [defaults2 synchronize]; 
    } 
} 

第一個提醒應彈出你運行應用程序的第一次，而第二個是一個調試器的佔位符，並應每次運行在第一次之後。對我來說，第二個是先運行，告訴我，第一個引導和showAgain！= 1。

Answer 1

NSInteger boot = [defaults1 integerForKey:@"firstBoot"];將返回0，直到您保存了默認值。 0，NO或nil返回沒有存儲任何值的密鑰。

處理此問題的正確方法是在嘗試檢索這些用戶默認值之前註冊默認值。

// register default values. until you save your own value "firstBoot" will return YES 
// you should put these two lines in the `application:didFinishLaunchingWithOptions:` 
// method of the AppDelegate. Add all userdefaults that should have default values there 
NSDictionary *defaultUserDefaults = @{ @"firstBoot" : @YES }; 
[[NSUserDefaults standardUserDefaults] registerDefaults:defaultUserDefaults]; 

// use BOOL instead of integer 
BOOL firstBoot = [[NSUserDefaults standardUserDefaults] boolForKey:@"firstBoot"]; 
if (firstBoot) { 
    NSLog(@"first launch"); 
    [[NSUserDefaults standardUserDefaults] setBool:NO forKey:@"firstBoot"]; 
    [[NSUserDefaults standardUserDefaults] synchronize]; 
} 
else { 
    NSLog(@"has been launched before"); 
} 

Answer 2

firstBoot在第一次啓動時會被設置爲YES？誰會設置它？

調用registerDefaults：在應用程序的開始處，所有屬性的值都應該具有不同於0的值，然後才能被明確設置。例如，使用firstBoot = YES鍵。或者，使用屬性「notFirstBoot」，其中缺少屬性的返回值（「NO」）是您實際需要的值。

而且真的沒有必要一次又一次地調用standardUserDefaults。