创建一个user defaults方法有多个，最简单得快速创建方法:

   NSUserDefaults *accountDefaults = [NSUserDefaults standardUserDefaults];

添加数据到 user defaults:

   [accountDefaults setObject:nameField.text forKey:UserDefaultNameKey];

也可以添加基本数据类型int, float, bool等，有相应得方法

   [accountDefaults setBool:YES forKey:UserDefaultBoolKey];

从user defaults中获取数据:

   [accountDefaults objectForKey:NCUserDefaultNameKey]  

   [accountDefaults boolForKey: UserDefaultBoolKey];

要点：

1）NSUserDefaults非常好用，并不需要用户在程序中设置NSUserDefaults的全局变量，需要在哪里使用NSUserDefaults的数据，那么就在哪里创建一个NSUserDefaults对象，然后进行读或者写操作。

2）针对同一个关键字对应的对象或者数据，可以对它进行重写，重写之后关键字就对应新的对象或者数据，旧的对象或者数据会被自动清理。

- (void)defaultCheck:(id)sender

{   

 NSLog(@" check按钮被按下   ");

 NSUserDefaults *accountDefaults = [NSUserDefaults standardUserDefaults];

if ([accountDefaults boolForKey:NCUserDefaultBoolForRegister] == NO)

 {

  ((UIButton*)sender).selected = YES;

  [accountDefaults setBool:YES forKey:NCUserDefaultBoolForRegister];

  [accountDefaults setObject:nameField.text forKey:NCUserDefaultNameKey];

  [accountDefaults setObject:pwdField.text forKey:NCUserDefaultPasswordKey];

 }

 else {//YES

  ((UIButton*)sender).selected = NO;

  [accountDefaults setBool:NO forKey:NCUserDefaultBoolForRegister];

  [accountDefaults setObject:nil forKey:NCUserDefaultNameKey];

  [accountDefaults setObject:nil forKey:NCUserDefaultPasswordKey];

 }

}

- (void)loadView {

 [super loadView];

 nameField = [[UITextField alloc]initWithFrame:CGRectMake(0, 0, 100, 30)];

 pwdField = [[UITextField alloc]initWithFrame:CGRectMake(0, 0, 100, 30)];

 [nameField setCenter:CGPointMake(160, 100)];

 [pwdField setCenter:CGPointMake(160, 150)];

 NSUserDefaults *accountDefaults = [NSUserDefaults standardUserDefaults];

 //存的是bool值一定要用boolForKey:获取

 //如果之前已经保存了User Defaults,那么在读取的时候就要将数据读取出来，显示在用户名和密码框中（这里没有加密）。

 if ([accountDefaults boolForKey:NCUserDefaultBoolForRegister] == YES) {

  nameField.text = [accountDefaults objectForKey:NCUserDefaultNameKey];

  pwdField.text = [accountDefaults objectForKey:NCUserDefaultPasswordKey];

 }

else

 {

    [nameField setPlaceholder:@"用户名"];

    [pwdField setPlaceholder:@"密码"];

 }

 nameField.borderStyle = UITextBorderStyleBezel;

 [pwdField setBorderStyle:UITextBorderStyleRoundedRect];

 [self.view addSubview:nameField];

 [self.view addSubview:pwdField];

 UIButton * loginBtn = [UIButton buttonWithType:UIButtonTypeRoundedRect];

 [loginBtn setFrame:CGRectMake(0, 0, 50, 30)];

 [loginBtn setCenter:CGPointMake(200, 200)];

 [loginBtn addTarget:self action:@selector(loginToWeiBo:) forControlEvents:UIControlEventTouchUpInside];

 [self.view addSubview:loginBtn];

 UIButton * checkBtn = [UIButton buttonWithType:UIButtonTypeRoundedRect];

 [checkBtn setFrame:CGRectMake(0, 0, 20, 20)];

 [checkBtn setCenter:CGPointMake(160, 180)];

  //选中之后得图标

 [checkBtn setBackgroundImage:[UIImage imageNamed:@"lock.png"] forState:(UIControlState)UIControlStateHighlighted];

 [checkBtn setBackgroundImage:[UIImage imageNamed:@"lock.png"] forState:(UIControlState)UIControlStateSelected];

  //未选中

 [checkBtn setBackgroundImage:[UIImage imageNamed:@"unlock.png"] forState:(UIControlState)UIControlStateNormal];

 [checkBtn addTarget:self action:@selector(defaultCheck:) forControlEvents:UIControlEventTouchUpInside];

  //用户名和密码已经保存

 if([accountDefaults boolForKey:NCUserDefaultBoolForRegister] == YES) 

 {

  [checkBtn setSelected:YES];

 }

 [self.view addSubview:Btn];

}