objective-c - 完成 block 不执行

Question

这是 block 的调用:

[VacationHelper openVacationWithName:vacationName
                usingBlock:^(UIManagedDocument *vacationDocument) {
   NSLog(@"vacationDocument.description:%@", vacationDocument.description);
}];

在接收方法的.h中:

typedef void (^completion_block_t)(UIManagedDocument *vacationDocument);

在 .m 中:

+ (void)openVacationWithName:(NSString *)vacationName
                  usingBlock:(completion_block_t)completionBlock;
{
    NSLog(@"Opening Vacation Document");

    // Get documents directory and path.
    NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
    url        = [url URLByAppendingPathComponent:vacationName];

    // Create the document and open if a match exists on file.
    UIManagedDocument *vacationDocument = [[UIManagedDocument alloc] initWithFileURL:url];
    if ([[NSFileManager defaultManager] fileExistsAtPath:[url path]]) {
        NSLog(@"vacationDocument.documentState:%i", vacationDocument.documentState);
        [vacationDocument openWithCompletionHandler:^(BOOL success) {
            if (success) NSLog(@"Document was opened.");
            else NSLog (@"Couldn't open document at %@", url);
        }];
    } else {

        // No match exists, so save the document to file.
        [vacationDocument saveToURL:url forSaveOperation:UIDocumentSaveForCreating
                  completionHandler:^(BOOL success) {
                      if (success) NSLog(@"Document was created.");
                      else NSLog(@"Couldn't create document at %@", url);
                  }];
    }
    NSLog(@"Exiting helper.");
}

我的问题是，为什么执行没有到达调用 openVacationWithName: 时传递的 block ？我从来没有看到写过 NSLog。

我怀疑 openVacationWithName: 没有完成，但是“退出助手”的 NSLog。确实打印。任何指导表示赞赏。仅供引用，这是 iTunes U/Stanford CS193P 作业 #6。

Answer 1

你没有调用 completionBlock里面openVacationWithName:usingBlock: .也许您想在方法结束时执行此操作:

  ...
  if (completionBlock) {
    completionBlock(vacationDocument);
  }

  NSLog(@"Exiting helper.");
}

(在这种情况下，返回 UIManagedDocument 可能更有意义)

或者可能在那些 completionHandler 里面方法中的 s openWithCompletionHandler:和 saveToUrl:forSaveOperation:completionHandler: :

... ^(BOOL success) {
  if (success) {
    NSLog(@"Document was created.");
  }
  else {
    NSLog(@"Couldn't create document at %@", url);
  }

  if (completionBlock) {
    completionBlock(vacationDocument);
  }
} ...