使用 NSUserDefaults 在构建时存储默认值

Question

我正在存储一个默认值的小字典，用户可以稍后修改，但可能只会更改一次。 NSUserDefaults.standardUserDefaults 似乎是存储这种东西的正确位置，我的问题是：有没有办法在构建时而不是运行时存储值？这段代码看起来应该是不必要的。

if !NSUserDefaults.standardUserDefaults().dictionaryForKey(default) {
        NSUserDefaults.standardUserDefaults().setObject(defaultDictionary, forKey: "default")
    }

或者，我应该考虑有更好的选择吗？

Answer 1

为了在构建时存储值，我会创建一个 .plist 或 .json 文件并预先填充您要存储的值，然后可以在运行时访问这些值。

Answer 2

按照 documentation

中所述注册默认值

Registering Your App’s Default Preferences

At launch time, an app should register default values for any preferences that it expects to be present and valid. When you request the value of a preference that has never been set, the methods of the NSUserDefaults class return default values that are appropriate for the data type. For numerical scalar values, this typically means returning 0, but for strings and other objects it means returning nil. If these standard default values are not appropriate for your app, you can register your own default values using the registerDefaults: method. This method places your custom default values in the NSRegistrationDomain domain, which causes them to be returned when a preference is not explicitly set.

When calling the registerDefaults: method, you must provide a dictionary of all the default values you need to register. Listing 2-1 shows an example where an iOS app registers its default values early in the launch cycle. You can register default values at any time, of course, but should always register them before attempting to retrieve any preference values.

Listing 2-1 Registering default preference values
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    // Register the preference defaults early.
    NSDictionary *appDefaults = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:@"CacheDataAgressively"];
    [[NSUserDefaults standardUserDefaults] registerDefaults:appDefaults];
 // Other initialization... 
} 
When registering default values for scalar types, use an NSNumber object to specify the value for the number. If you want to register a preference whose value is a URL, use the archivedDataWithRootObject: method of NSKeyedArchiver to encode the URL in an NSData object first. Although you can use a similar technique for other types of objects, you should avoid doing so when a simpler option is available.

使用 NSUserDefaults 在构建时存储默认值

Using NSUserDefaults to store default values at build time

nsuserdefaults

ios

swift