如何使用块为整个应用程序共享的每个磁盘文件创建一个全局UIManagedDocument实例？

Question

我试图设计一个帮助方法,它将检索UIManagedDocument,然后打开并返回它,以便我可以从我的应用程序中的几个地方访问相同的UIManagedDocument.

由于我对块不太熟悉,因此我遇到了异步性问题.理想情况下,事件的顺序是这样的:

1. 类X调用helper方法来检索UIManagedDocument,并包含一个在返回打开的文档时运行的代码块.
2. 类方法检索UIManagedDocument并根据需要调用openWithCompletionHandler或saveToURL,并包含在返回打开的文档时运行的代码块.
3. openwithCompletionHandler或saveToURL完成他们的任务,并返回成功= YES并在其块中运行代码
4. 类方法完成其任务并返回一个打开的UIManagedDocument并在其块中运行代码

我可以通过某种方式传递原始块吗？

到目前为止,这是我的代码.任何想法都非常感谢,谢谢.

// This is a dictionary where the keys are "Vacations" and the objects are URLs to UIManagedDocuments
static NSMutableDictionary *managedDocumentDictionary = nil;

// This typedef has been defined in .h file: 
// typedef void (^completion_block_t)(UIManagedDocument *vacation);
// The idea is that this class method will run the block when its UIManagedObject has opened

@implementation MyVacationsHelper

+ (void)openVacation:(NSString *)vacationName usingBlock:(completion_block_t)completionBlock
{
    // Try to retrieve the relevant UIManagedDocument from managedDocumentDictionary
    UIManagedDocument *doc = [managedDocumentDictionary objectForKey:vacationName];

    // Get URL for this vacation -> "<Documents Directory>/<vacationName>" 
    NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
    url = [url URLByAppendingPathComponent:vacationName];

    // If UIManagedObject was not retrieved, create it
    if (!doc) {

        // Create UIManagedDocument with this URL
        doc = [[UIManagedDocument alloc] initWithFileURL:url];

        // Add to managedDocumentDictionary
        [managedDocumentDictionary setObject:doc forKey:vacationName];
    }

    // If document exists on disk...

    if ([[NSFileManager defaultManager] fileExistsAtPath:[url path]]) 
    {
        [doc openWithCompletionHandler:^(BOOL success) 
        {
            // Can I call the completionBlock from above in here?
            // How do I pass back the opened UIDocument
        }];

    } else {

        [doc saveToURL:url 
      forSaveOperation:UIDocumentSaveForCreating
     completionHandler:^(BOOL success)
        { 
            // As per comments above
        }];

    }

}

Answer 1

您可以使用completionBlock(doc)执行该块.

    [doc openWithCompletionHandler:^(BOOL success) 
     {
         // Can I call the completionBlock from above in here?
         // How do I pass back the opened UIDocument
        completionBlock(doc);
     }];

假设您在将调用openVacation方法的类中实现了以下方法:

-(void)vacationOpened:(UIManagedDocument *)vacation
{
    NSLog(@"My Vacation: %@", vacation.description);
}

调用openVacation方法的示例代码行将是:

[MyVacationsHelper openVacation:@"MyVacation1" usingBlock:^(UIManagedDocument *vacation){
    [self vacationOpened:vacation];
}];

插入符后的(UIManagedDocument*vacation)意味着当您使用括号表示法执行块时 - 如在completionBlock(doc)中 - ,您需要列出(UIManagedDocument*)作为参数.该参数的值将在指定的块内称为休假.我在上面的块代码示例中所做的是在我当前的类(self)中调用一个方法并将参数传递给该方法,以便我可以根据需要使用它(我只是在这里做了一个NSLog以确保它工作) .