如何正确工作（检索值）与NSUserDefaults [英] How to properly work (retrieve values) with NSUserDefaults

问题描述

我在代码中有一个简单的方法，如下所示：

I have a simple method in my code which looks like the following:

- (BOOL)isFirstTimeLogin 
{
    NSString *t_gName = 
    [NSString stringWithFormat:@"%@", [[NSUserDefaults standardUserDefaults] objectForKey:kGroupIdentifierKey]];
    if ([t_gName isEqualToString:@""] || t_gName == nil) {
        DLog(@"LoginViewController, m:::isFirstTimeLogin, First time login happening.");
        return YES;
    }

    DLog(@"LoginViewController, m:::isFirstTimeLogin, Not a first time login.");
    return NO;
}

这样做只需转到设置包，一个PSTextFieldSpecifier。如果我手动进入和添加一些任意文本，代码工作正常。但是，每当我第一次在新设备上安装应用程序时，第一个条件是执行为false，这应该是真的。在遍历代码后，gdb证明对象确实是nil：

Simply what this does is go to the Settings bundle, and retrieve a value from a PSTextFieldSpecifier. If I manually go in and add some arbitrary text, the code works as expected. However, whenever I first install the app on a new device, the first condition is executing as false, which it should be true. After stepping through the code, gdb proves that the object is indeed nil as well:

（gdb）po t_gName

（null）

(gdb) po t_gName
(null)

我可能在这里做错了什么？为什么它的条件是第一次安装应用程序失败，t_gName是一个空/ null PSTextFieldSpecifier。我甚至去尝试在一个空字符串的设置包中添加一个DefaultValue。

What am I possibly doing wrong here? Why is it the condition is failing for the first time the app is installed and t_gName is an empty/null PSTextFieldSpecifier. I even went as far as trying to add a DefaultValue in my Settings bundle of an empty string.

推荐答案

[NSString stringWithFormat:@"%@", nil];

这会创建如下：

@"(null)"

c $ c> nil 也不等于 @。

and is therefore neither nil nor equal to @"".

1. 您不需要 stringWithFormat：。


2. 不要检查 string == nil ，但！string


3. 您不必检查一个空字符串，因为有一个或 nil 。


4. 使用比 t_gName 更好的名称，没有理由缩短名称。

1. You don't need stringWithFormat: at all.
2. Don't check for string == nil but for !string
3. You don't have to check for an empty string, as there is one set or it's nil.
4. Use a better name than t_gName, there's no reason for short names.

像这样：

- (BOOL)isFirstTimeLogin 
{
    NSString *groupIdentifier = [[NSUserDefaults standardUserDefaults]
                                    objectForKey:kGroupIdentifierKey];
    if (!groupIdentifier) {
        DLog(@"First time login.");
        return YES;
    }

    DLog(@"Not a first time login.");
    return NO;
}

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