Question

当UIViewController创建的类作为另一个类的完成块时，当UIViewController获取dealloc调用时，内存管理生命周期如何工作？

假设UIViewController继承类实例化一个类ControllerMediatorClass。

ControllerMediatorClass又调用另一个类ClassThatDealsWithNetworking，其工作需要一些时间才能完成。

如果UIViewController在ClassThatDealsWithNetworking完成之前获取其dealloc，那么其所有权下的类何时会被清除？

当MyUIViewController将它设置为nil时，是否会立即释放'ControllerMediatorClass'的实例，因为ControllerMediatorClass仍然作为ClassThatDealsWithNetworking实例的完成块？

MyUIViewController：

@property (nonatomic, strong) ControllerMediatorClass *mediatorClass;

- (IBAction)userTappedSomething
{
    [mediatorClass makeANetworkCall];
}

- (void)dealloc
{
   self.mediatorClass = nil;
}

ControllerMediatorClass：

- (void)makeANetworkCall
{
    ClassThatDealsWithNetworking *networkCommand;

    [networkCommand execute:^(NSDictionary *data) 
        {          
            // handling completion that 
        } error:^(MyError *error) 
        {        
            // handling completion
        }
    ];
}

（使用ARC）

Answer 1

当MyUIViewController将它设置为nil时，是否会立即释放'ControllerMediatorClass'的实例，因为ControllerMediatorClass仍然作为ClassThatDealsWithNetworking实例的完成块？

是。因为块会自动捕获它使用的对象，并且只要保留块就会保留它们。

因此，[ClassThatDealsWithNetworking execute:]方法可能会保留传递给它的完成块，然后在后台执行网络调用，然后在块完成后调用块并释放块此块中使用的每个变量也会保留。当块被释放时将被释放。

想象一下这个ClassThatDealsWithNetworking类的伪代码：

typedef void(^NetworkingCompletionBlock)(NSDictionary* data)
@interface ClassThatDealsWithNetworking
@property(nonatomic, copy) NetworkingCompletionBlock completionBlock;
-(void)execute:(NetworkingCompletionBlock)block;
@end

@implementation ClassThatDealsWithNetworking
-(void)execute:(NetworkingCompletionBlock)block {
  // make a copy of the block passed as a parameter
  // so that we keep the completionBlock around inside
  // the ClassThatDealsWithNetworking instance
  // until the network request has finished
  // ==> THIS WILL implicitly RETAIN every object used in the completionBlock
  self.completionBlock = block; 
  ...
  // Then perform the network request
  [NSURLConnection connectionWithRequest:... delegate:self];
  ...
}

-(void)connection:(NSURLConnection*)cxn didFailWithError:(NSError*)error
{
  // call the completion block here
  self.completionBlock(nil,error);
  // then release the completionBlock
  // ==> THIS WILL RELEASE every object previously implicitly retained by the completionBlock
  self.completionBlock = nil;
}
-(void)connectionDidFinishLoading:(NSURLConnection*)cxn
{
  NSDictionary* data = ...
  // call the completion block here
  self.completionBlock(data,nil);
  // then release the completionBlock
  // ==> THIS WILL RELEASE every object previously implicitly retained by the completionBlock
  self.completionBlock = nil;
}
@end

然后，如果你这样做：

[networkCommand execute:^(NSDictionary *data) 
{
    self.someProperty = data;
} error:^(MyError *error) 
{
    NSLog(@"%@", error);
    self.someProperty : nil;
}];

然后self（您示例中的ControllerMediatorClass）将被本身隐式保留，只要该块存在，因为您的引用{{1}在某个地方的街区。因此编译器知道在执行块时它将需要它并保留它。并且当块发布时将被隐式释放。

这可以确保在执行块时块中正在使用的所有对象仍然存在，从而避免崩溃。

请注意，如果您不小心，这可能会导致保留周期。例如，如果您忘记self类中的自self.completionBlock = nil（在委托方法或ClassThatDealsWithNetworking方法中），则dealloc永远不会释放该块实例，并将继续保留ClassThatDealsWithNetworking。

有关详细信息，请阅读Apple文档中的Blocks Programming Guide。

一个类和块的生命周期

1 个答案: