Objective-C：自定义BOOL访问器(getter和setter)方法

我没有任何实例变量,但也许我应该？我可以为NSDate * lastUnlocked添加一个.

到目前为止,这是相关的代码：

// PasscodeLock.h

extern NSString *const kPasscodeLastUnlocked;

@interface PasscodeLock : NSObject {

}

- (BOOL)isImmediate;
- (void)setImmediate:(BOOL)on;

- (NSDate *)lastUnlocked;
- (void)resetLastUnlocked;
- (void)setLastUnlocked:(NSDate *)lastUnlocked;

@end


// PasscodeLock.m

#import "PasscodeLock.h"

NSString *const kPasscodeLastUnlocked    = @"kPasscodeLastUnlocked";

@implementation PasscodeLock

#pragma mark PasscodeLock

- (BOOL)isImmediate {
    return self.lastUnlocked == nil;
}

- (void)setImmediate:(BOOL)on {
    if (on) {
        [self resetLastUnlocked];
    } else {
        self.lastUnlocked = nil;        
    }
}

- (NSDate *)lastUnlocked {
    return [[NSUserDefaults standardUserDefaults] objectForKey:kPasscodeLastUnlocked];
}

- (void)resetLastUnlocked {
    NSDate *now = [[NSDate alloc] init];
    self.lastUnlocked = now;
    [now release];
}

- (void)setLastUnlocked:(NSDate *)lastUnlocked {
    [[NSUserDefaults standardUserDefaults] setObject:lastUnlocked forKey:kPasscodeLastUnlocked];
}

然后,在一个将PasswordLock * passwordLock作为实例变量的视图控制器中,我想做passcode.immediate = NO,但是我在“PasscodeLock *”类型的对象上找不到“属性’立即’的错误.”

如何获得passcode.immediate = NO？