objective-c - 确定弱引用对象是否已被释放

Question

我使用下面的代码来下载图片:

- (void)downloadImageAtUrl:(id)url
               andDelegate:(id<IPServerDelegate>)delegate_ {
  NSURL *correctUrl = nil;
  if ([url isKindOfClass:[NSString class]])
    correctUrl = [NSURL URLWithString:[NSString stringWithFormat:@"%@%@", kHostURL, [url substringFromIndex:1]]];
  else
    correctUrl = url;
  __block ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:correctUrl];
  [imageRequestsArray addObject:request];
  [request setCompletionBlock:^{
    if (request.responseStatusCode == 200) {
      if (delegate_ && [delegate_ respondsToSelector:@selector(didDownloadImage:atUrl:)]) {
        [delegate_ didDownloadImage:request.responseData atUrl:request.url];
      }
    }
    else {
      if (delegate_ && [delegate_ respondsToSelector:@selector(failedToDownloadImageWithUrl:)]) {
        [delegate_ failedToDownloadImageWithUrl:request.url];
      }
    }
    [imageRequestsArray removeObject:request];
  }];

  [request setFailedBlock:^{
    if (delegate_ && [delegate_ respondsToSelector:@selector(failedToDownloadImageWithUrl:)]) {
      [delegate_ failedToDownloadImageWithUrl:request.url];
    }
    [imageRequestsArray removeObject:request];
  }];

  [request startAsynchronous];
}

如果 delegate_ 对象已被释放，则应用程序会崩溃。如何确定对象 delegate_ 已被释放而无需创建对它的直接引用？我知道 iOS 5 中的 __weak 指针，但我的应用程序必须与 iOS 4.3 兼容。

Answer 1

好吧，当你的 delegate_ 被释放时，我假设它是释放的。什么时候，之后:

[object release];

这样做:

object=nil;

然后在你的代码上，检查它是否存在:

if(delegate_){

}