NSString *valueToSave = @"someValue";
[[NSUserDefaults standardUserDefaults] setObject:valueToSave forKey:@"preferenceName"];
[[NSUserDefaults standardUserDefaults] synchronize];

然后再拿回来

NSString *savedValue = [[NSUserDefaults standardUserDefaults]
    stringForKey:@"preferenceName"];

在Swift 4.0.3 Xcode 9

============set  Data in UserDefaults =========

  UserDefaults.standard.set(userName, forKey: "userName")
  UserDefaults.standard.synchronize()

============Get Data in UserDefaults =========

  let userName = UserDefaults.standard.string(forKey: "userName")
  print(userName ?? "Gera")

  userNameTextField.text = ""+userName!

Swift 3更新

func setObject(value:AnyObject ,key:String)
{
    let pref = UserDefaults.standard
    pref.set(value, forKey: key)
    pref.synchronize()
}

func getObject(key:String) -> AnyObject
{
    let pref = UserDefaults.standard
    return pref.object(forKey: key)! as AnyObject
}

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];

// saving an NSString
[prefs setObject:@"TextToSave" forKey:@"keyToLookupString"];

// saving an NSInteger
[prefs setInteger:42 forKey:@"integerKey"];

// saving a Double
[prefs setDouble:3.1415 forKey:@"doubleKey"];

// saving a Float
[prefs setFloat:1.2345678 forKey:@"floatKey"];

// This is suggested to synch prefs, but is not needed (I didn't put it in my tut)
[prefs synchronize];

检索

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];

// getting an NSString
NSString *myString = [prefs stringForKey:@"keyToLookupString"];

// getting an NSInteger
NSInteger myInt = [prefs integerForKey:@"integerKey"];

// getting an Float
float myFloat = [prefs floatForKey:@"floatKey"];

在Swift5和Xcode 10.2中

//Save
UserDefaults.standard.set(true, forKey: "Key1") //Bool
UserDefaults.standard.set(1, forKey: "Key2")  //Integer
UserDefaults.standard.set("This is my string", forKey: "Key3") //String
UserDefaults.standard.synchronize()
        
//Retrive
UserDefaults.standard.bool(forKey: "Key1")
UserDefaults.standard.integer(forKey: "Key2")
UserDefaults.standard.string(forKey: "Key3")
            
//Remove
UserDefaults.standard.removeObject(forKey: "Key3")

注意:保存文本数据(意味着字符串，数组，字典等)在UserDefaults。

不要将图片保存在UserDefaults中，不推荐(保存图片在本地目录)。

不要忘记这句话，否则它可能并不总是有效:

[standardUserDefaults synchronize];