正確使用notificationCenter addObserverForName與塊

Question

如何以乾淨的方式在塊中實例化2個BOOL變量？

作爲後續，它的工作，但我有「捕獲‘自我’強烈該塊很可能會導致保留週期」，這顯然是不好的......

[notificationCenter addObserverForName:UIApplicationDidEnterBackgroundNotification 
            object:nil 
            queue:mainQueue usingBlock:^(NSNotification *note) { 
             isApplicationOnForegroundMode = NO; 
             isApplicationOnBackgroundMode = YES; 
            } ]; 


    [notificationCenter addObserverForName:UIApplicationDidBecomeActiveNotification 
            object:nil 
            queue:mainQueue usingBlock:^(NSNotification *note) { 
             isApplicationOnForegroundMode = YES; 
             isApplicationOnBackgroundMode = NO; 
            } ]; 

Answer 1

我猜想isApplicationOnForegroundMode和isApplicationOnBackgroundMode是ivars。

您需要添加幾個ivars或屬性來跟蹤觀察塊，以便將其移除。我將調用那些屬性爲backgroundObserver和activeObserver的id。

更新您的代碼：

__unsafe_unretained <<self's class>> *this = self; // or __weak, on iOS 5+. 

self.backgroundObserver = [notificationCenter 
          addObserverForName:UIApplicationDidEnterBackgroundNotification 
             object:nil 
              queue:mainQueue 
            usingBlock:^(NSNotification *note) { 
             this->isApplicationOnForegroundMode = NO; 
             // or: this.isApplicationOnForegroundMode = YES, if you have a property declared 
             this->isApplicationOnBackgroundMode = YES; 
            } ]; 


self.activeObserver = [notificationCenter 
         addObserverForName:UIApplicationDidBecomeActiveNotification 
            object:nil 
             queue:mainQueue usingBlock:^(NSNotification *note) { 
              this->isApplicationOnForegroundMode = YES; 
              this->isApplicationOnBackgroundMode = NO; 
             } ]; 

您還需要確保你叫

[[NSNotificationCenter defaultCenter] removeObserver:self.backgroundObserver]; 
[[NSNotificationCenter defaultCenter] removeObserver:self.activeObserver]; 

在 -dealloc

。