如何在NSMutableArray上添加觀察者？

Question

我搜索了很多，但沒有找到有用的代碼或教程。

在我的應用程序中，我有一個可變數組，每60秒更新一次。

數組中的對象由多個視圖控制器中的表視圖顯示。

我只想在數組中的值更改或更新時自動重新加載表視圖。

為此，我想在可變數組上添加觀察者，即當數組中的值發生變化時，它應該調用特定的方法，例如

-(void)ArrayUpdatedNotification:(NSMutableArray*)array
{
    //Reload table or do something
} 

提前致謝。

Answer 1

您可以使用訪問器方法將數組抽象為數據容器類，然后使用鍵值觀察來觀察何時更改了支持容器對象的數組（您無法直接在NSArray上使用KVO）。

下面是一個用作數組頂部抽象的類的簡單示例。 您可以使用其insertObject:inDataAtIndex:和removeObjectFromDataAtIndex:方法，而不是直接訪問with addObject:和removeObject: .

// DataContainer.h
@interface DataContainer : NSObject

// Convenience accessor
- (NSArray *)currentData;

// For KVC compliance, publicly declared for readability
- (void)insertObject:(id)object inDataAtIndex:(NSUInteger)index;
- (void)removeObjectFromDataAtIndex:(NSUInteger)index;
- (id)objectInDataAtIndex:(NSUInteger)index;
- (NSArray *)dataAtIndexes:(NSIndexSet *)indexes;
- (NSUInteger)countOfData;

@end

// DataContainer.m

@interface DataContainer ()

@property (nonatomic, strong) NSMutableArray *data;

@end

@implementation DataContainer

//  We'll use automatic notifications for this example
+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key
{
    if ([key isEqualToString:@"data"]) {
        return YES;
    }
    return [super automaticallyNotifiesObserversForKey:key];
}

- (id)init
{
    self = [super init];
    if (self) {
        // This is the ivar which provides storage
        _data = [NSMutableArray array];
    }
    return self;
}

//  Just a convenience method
- (NSArray *)currentData
{
    return [self dataAtIndexes:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, [self countOfData])]];
}

//  These methods enable KVC compliance
- (void)insertObject:(id)object inDataAtIndex:(NSUInteger)index
{
    self.data[index] = object;
}

- (void)removeObjectFromDataAtIndex:(NSUInteger)index
{
    [self.data removeObjectAtIndex:index];
}

- (id)objectInDataAtIndex:(NSUInteger)index
{
    return self.data[index];
}

- (NSArray *)dataAtIndexes:(NSIndexSet *)indexes
{
    return [self.data objectsAtIndexes:indexes];
}

- (NSUInteger)countOfData
{
    return [self.data count];
}

@end

我們這樣做的原因是我們現在可以觀察對底層數組所做的更改。 這是通過Key Value Observing完成的 。 顯示了一個實例化和觀察數據控制器的簡單視圖控制器：

// ViewController.h
@interface ViewController : UIViewController

@end

// ViewController.m

@interface ViewController ()

@property (nonatomic,strong) DataContainer *dataContainer;

@end

@implementation ViewController

static char MyObservationContext;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        //  Instantiate a DataContainer and store it in our property
        _dataContainer = [[DataContainer alloc] init];
        //  Add self as an observer. The context is used to verify that code from this class (and not its superclass) started observing.
        [_dataContainer addObserver:self
                         forKeyPath:@"data"
                            options:(NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew)
                            context:&MyObservationContext];
    }

    return self;
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    //  Check if our class, rather than superclass or someone else, added as observer
    if (context == &MyObservationContext) {
        //  Check that the key path is what we want
        if ([keyPath isEqualToString:@"data"]) {
            //  Verify we're observing the correct object
            if (object == self.dataContainer) {
                NSLog(@"KVO for our container property, change dictionary is %@", change);
            }
        }
    }
    else {
        //  Otherwise, call up to superclass implementation
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    //  Insert and remove some objects. Console messages should be logged.
    [self.dataContainer insertObject:[NSObject new] inDataAtIndex:0];
    [self.dataContainer insertObject:[NSObject new] inDataAtIndex:1];
    [self.dataContainer removeObjectFromDataAtIndex:0];
}

- (void)dealloc
{
    [_dataContainer removeObserver:self forKeyPath:@"data" context:&MyObservationContext];
}

@end

運行此代碼時，視圖控制器會觀察到對數據的三次更改並將其記錄到控制台：

KVO for our container property, change dictionary is {
        indexes = "<NSIndexSet: 0x8557d40>[number of indexes: 1 (in 1 ranges), indexes: (0)]";
        kind = 2;
        new =     (
            "<NSObject: 0x8557d10>"
        );
    }
KVO for our container property, change dictionary is {
        indexes = "<NSIndexSet: 0x715d2b0>[number of indexes: 1 (in 1 ranges), indexes: (1)]";
        kind = 2;
        new =     (
            "<NSObject: 0x71900c0>"
        );
    }
KVO for our container property, change dictionary is {
        indexes = "<NSIndexSet: 0x8557d40>[number of indexes: 1 (in 1 ranges), indexes: (0)]";
        kind = 3;
        old =     (
            "<NSObject: 0x8557d10>"
        );
    }

雖然這有點復雜（並且可以更多地涉及），但這是自動通知可變數組的內容被更改的唯一方法。

Answer 2

可以做的是 - 更新陣列后發送通知（NSNotificationCenter），所有控制器都會收到此通知。 收到通知后，控制器應該執行[tableview reloaddata]。

代碼示例 ：

// Adding an observer
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateTable:) name:@"arrayUpdated" object:nil];

// Post a notification
[[NSNotificationCenter defaultCenter] postNotificationName:@"arrayUpdated" object:nil]; 

// the void function, specified in the same class where the Notification addObserver method has defined
- (void)updateTable:(NSNotification *)note { 
    [tableView reloadData]; 
}

Answer 3

如果你想使用閃亮的塊，你可以這樣做

// Create an instance variable for your block holder in your interface extension
@property (strong) id notificationHolder;

// Listen for notification events (In your TableView class.
self.notificationHolder = [[NSNotificationCenter defaultCenter] addObserverForName:@"NotificationName"
                             object:nil
                              queue:[NSOperationQueue mainQueue]
                         usingBlock:^(NSNotification *note) {

        NSLog(@"Received notification");
}];

然后在dealloc（或當你不再使用它時）

- (void)dealloc {
     [[NSNotificationCenter defaultCenter] removeObserver:self.notificationHolder];
}

然后在其他一些班級

// Send a notification
[[NSNotificationCenter defaultCenter] postNotificationName:@"NotificationName" object:nil];

詢問是否有不清楚的事情！ 希望能幫助到你！

編輯由於評論

“ YourEvent ”是通知的名稱，這意味着您可以將其命名為您想要的任何名稱。 （也許“ UpdateArrayNotification可能是一個好名字？）

需要考慮的事項：請注意，您可以為同一通知提供多個觀察者。 這意味着所有觀察者都會搶斷一個“帖子”。