关于NSUserDefaults

什么是NSUserDefaults

NSUserDefaults class可以帮助我们存储一些应用或者数据的设定和属性，比如为一些应用设置背景颜色之类的。这些对象会被存储为IOS的系统默认值. 这些数据会被持久化. 也就是说即使关掉应用或者重新启动电话，原来存储的数据仍然存在。

With NSUserDefaults you can save objects from the following class types:
NSData
NSString
NSNumber
NSDate
NSArray
NSDictionary
If you want to store any other type of object, such as a UIImage, you will typically need to archive it or wrap it in an instance of NSData, NSNumber, or NSString.

保存

 NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    [defaults setObject:firstName forKey:@"firstName"];

    [defaults setObject:lastName forKey:@"lastname"];

    [defaults setInteger:age forKey:@"age"];

    [defaults setObject:imageData forKey:@"image"];

    [defaults synchronize];

    NSLog(@"Data saved");

提取

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    NSString *firstName = [defaults objectForKey:@"firstName"];

    NSString *lastName = [defaults objectForKey:@"lastname"];

    int age = [defaults integerForKey:@"age"];

    NSString *ageString = [NSString stringWithFormat:@"%i",age];

    NSData *imageData = [defaults dataForKey:@"image"];

    UIImage *contactImage = [UIImage imageWithData:imageData];