NSUserDefaults不加载我想要的数字

debugcn 发表于 Dev

柠檬雷声

我正在尝试使用NSUserDefaults在应用程序关闭后保存两个变量。一个是firstBoot，另一个是showAgain。为错误的代码做准备-

- (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];
    }
}

警报-

- (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];
    }
}

第一个警报应该在您第一次运行应用程序时弹出，而第二个警报是调试器占位符，并且应该在第一次运行后每次运行。对我来说，第二个首先运行，告诉我firstBoot和showAgain！= 1。

马蒂亚斯·鲍赫（Matthias Bauch）

NSInteger boot = [defaults1 integerForKey:@"firstBoot"];将返回0，直到您将默认值保存为一个值为止。0，NO否则nil返回未存储任何值的键。

解决此问题的正确方法是在尝试检索这些用户默认值之前先注册默认值。

// 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");
}

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