Question

我正在尝试理解如何在此链接中实现真正的Cocoa MVC，如图4-7所示。

这是一个链接

http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaDesignPatterns/CocoaDesignPatterns.html#//apple_ref/doc/uid/TP40002974-CH6-SW1

图4-7显示该模型使用模式观察器来通知控制器（被动MVC）。我以这种方式在我的模型中实现观察者

@interface IADataManager : NSObject

//MARK: Parsed Feed With IANewsDataObj
@property (nonatomic,retain) NSMutableArray *feedArray;

//MARK: Model use Singelton Pattern
+ (IADataManager *) sharedInstance;

//MARK: Observation methods
- (void) addListener:(id<IADataManagerListener>) listener;
- (void) removeListener:(id<IADataManagerListener>) listener;

//MARK: Business Logic
- (void) loadFeedFromNetwork;
- (void) loadFeedFromDataBase;
- (void) loadImageForTarget:(id<IADataManagerListener>) target
                AtIndexPath:(NSIndexPath *) indPath;
- (void) saveFeedToDataBase;

@end

@protocol IADataManagerListener <NSObject>

- (void) IADataManager            :(IADataManager *) dataMng
         didRefreshWithError      :(NSError *) error;

- (void) IADataManager            :(IADataManager *) dataMng
         didLoadImageForIndexPath :(NSIndexPath *) indexPath;

- (void) IADataManager            :(IADataManager *) dataMng
         didLoadWithError         :(NSError *) error;


@end


  - (void) addListener:(id<IADataManagerListener>) listener
{
    if([self.listeners indexOfObject:listener] == NSNotFound && listener)
        [self.listeners addObject:listener];
}
- (void) removeListener:(id<IADataManagerListener>) listener
{
    if([self.listeners indexOfObject:listener] !=NSNotFound && listener)
        [self.listeners removeObject:listener];
}

//Notification example
- (void) handleLoadedNews:(NSArray *) loadedNews
{
    [self.feedArray   addObjectsFromArray:loadedNews];
    [self.listeners enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        objc_msgSend(obj, @selector(IADataManager:didRefreshWithError:),self,nil);
    }];


}

我想知道，如果有更好的方法在模型中实现观察者？例如，使用KVO或NSNotificationCenter。但问题是，在KVO和NSNotificationCenter的帮助下，我无法使用具有多个参数的选择器。例如，

 - (void) DataManager:(DataManager *) dm withObj1:(Obj1*) obj1  Obj1:(Obj2*) obj2  Obj3:(Obj3*) obj3

非常感谢！

Answer 1

But problem is that with the help of KVO and NSNotificationCenter i can not use selectors with more than 1 argument.

你可以!!!

将所有选择器存储在数组或字典中，然后传递该单个对象。

Answer 2

我认为使用委托或块是理想的。要在视图控制器中获得回调，您可以使用委托方法或块。我认为这将是MVC设计模式的理想方法。

Answer 3

KVO通常是更好的选择。例如：

在IDataManager中：

- (void) handleLoadedNews:(NSArray *) loadedNews
{
    [self willChangeValueForKey:@"feedsArray"]; //Also, see - (void)willChange:(NSKeyValueChange)changeKind valuesAtIndexes:(NSIndexSet *)indexes forKey:(NSString *)key
    [self.feedsArray addObjectsFromArray:arr];
    [self didChangeValueForKey:@"feedsArray"]; //Also, see - (void)didChange:(NSKeyValueChange)changeKind valuesAtIndexes:(NSIndexSet *)indexes forKey:(NSString *)key
}

并且，在ViewController中：

- (void) viewDidLoad {
    ....
    [[IADataManager sharedInstance] addObserver:self forKeyPath:@"feedsArray" options:0 context:NULL];
}

- (void) viewWillUnload {
    ....
    [[IADataManager sharedInstance] removeObserver:self forKeyPath:@"feedsArray"];
}

- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    //if keyPath is "feedsArray", refresh my views
}

Cocoa：在模型中使用观察者

3 个答案: