Question

这是使用块的调用：

[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：

+ (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openVacationWithName:调用中传递的块？我从来没有看过NSLog写的。

我怀疑openVacationWithName:没有完成，但NSLog是“退出帮手”。打印。任何指导赞赏。仅供参考，这是适用于iTunes U / Stanford CS193P的＃6。

Answer 1

您没有在completionBlock内拨打openVacationWithName:usingBlock:。也许你想在方法结束时这样做：

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

  NSLog(@"Exiting helper.");
}

（在这种情况下，或许返回UIManagedDocument）

会更有意义

或者可能在方法completionHandler和openWithCompletionHandler:中的saveToUrl:forSaveOperation:completionHandler:内：

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

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

完成块未执行

1 个答案: