UIAlertController 内存泄漏

Question

我没有使用 ARC。

在展示 UIAlertController 时，通过 Instruments 测试泄漏给了我以下信息：

当我检查调用树时，它似乎在抱怨这段代码。不确定其中有多少是相关的，但无论如何......

-(void) connection:(NSURLConnection*)connection didFailWithError:(NSError*)error {
  // bunch of code

  #ifndef NDEBUG
    NSString* err_msg = [NSString stringWithFormat:@"%@%ld", @"Error number ", (long) error_code];
    // @property (nonatomic, retain) id <DownloadMonitor> m_downloadMonitor;
    [_m_downloadMonitor showDownloadAlert:err_msg withTitle:@"Download error"];
  #endif

m_downloadMonitor实际上是一个DashboardController类型的对象，定义如下：

@interface DashboardController : BaseController <UIAlertViewDelegate, UITableViewDelegate, UITableViewDataSource, DownloadMonitor>

DownloadMonitor是自定义协议，定义如下：

@protocol DownloadMonitor <NSObject>
-(void) downloadFinishedFor:(UIProgressView*)progress_bar;
-(void) downloadFailedFor:(UIProgressView*)progress_bar;
-(void) showDownloadAlert:(NSString*)message withTitle:(NSString*)title;
@end

方法showDownloadAlert在DashboardController中定义如下：

-(void) showDownloadAlert:(NSString*)message withTitle:(NSString*)title {
  [self showPopupMessage:message withTitle:title andDelegate:self andActionHandlers:@{@"OK":@""}];
}

最后，BaseController 中的showPopupMessage（DashboardController 的父类）：

- (void)showPopupMessage: (NSString*)message withTitle:(NSString*)title andDelegate:(BaseController*)delegate andActionHandlers:(NSDictionary*)handlers {
  UIAlertController* alert = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];

  for ( id key in handlers ) {
    NSString* button_name = (NSString*) key;
    NSString* handler_name = (NSString*) [handlers objectForKey:key];
    UIAlertAction* action;

    if ( ! [handler_name isEqualToString:@""] ) {
      SEL sel = NSSelectorFromString(handler_name);
      action = [UIAlertAction actionWithTitle:button_name style:UIAlertActionStyleDefault handler:^(UIAlertAction * action)         {
          [delegate performSelector:sel];
          [alert dismissViewControllerAnimated:YES completion:NULL];
        }];
    }
    else {
      action = [UIAlertAction actionWithTitle:button_name style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {
      [alert dismissViewControllerAnimated:YES completion:NULL];
        }];
    }

    [alert addAction:action];
  }

  [delegate presentViewController:alert animated:YES completion:nil];
}

为什么 Instruments 会显示泄漏？ 我查看了这些线程：

iOS 8 Only Memory Leak with UIAlertController or UIActionSheet

UIAlertController memory leak/issues - Swift

他们似乎暗示这可能是一个错误......或者它可能是我错过的保留周期。

Answer 1

我认为你有一个保留圈：

在showPopupMessage 方法中，动作被添加到alert 并保留它们。您定义引用 alert 的块（因为它使用它）。块正在保留alert。

所以，alert 保留了保留 `'alert: your retain circle!

的块

你应该试试：

__block __typeof__(alert) blockAlert = alert;

action = [UIAlertAction actionWithTitle:button_name style:UIAlertActionStyleDefault handler:^(UIAlertAction * action)         {
    [delegate performSelector:sel];
    [blockAlert dismissViewControllerAnimated:YES completion:NULL];
}];

__block 存储类型修饰符将引用警报而不保留它（在非 ARC 模式下）：https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/Blocks/Articles/bxVariables.html#//apple_ref/doc/uid/TP40007502-CH6-SW6