正确使用notificationCenter addObserverForName与块

Question

如何以干净的方式在块中实例化2个BOOL变量？

作为后续，它的工作，但我有“捕获‘自我’强烈该块很可能会导致保留周期”，这显然是不好的......

[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。

您需要添加几个ivars或属性来跟踪观察块，以便将其移除。我将调用那些属性为backgroundObserver和activeObserver的id。

更新您的代码：

__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; 
             } ]; 

您还需要确保你叫

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

在 -dealloc

。