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我有两个基本上做同样事情的程序。他们读取 XML 提要并解析元素。这两个程序的设计都是使用异步 NSURLConnection 来获取数据，然后生成一个新线程来处理解析。在解析 5 个项目的批次时，它会回调主线程以重新加载 UITableView。

我的问题是它在一个程序中运行良好，但在另一个程序中运行良好。我知道解析实际上发生在后台线程上，并且我知道 [tableView reloadData] 正在主线程上执行；但是，在所有解析完成之前，它不会重新加载表。我难住了。据我所知……这两个程序的结构完全相同。这是来自应用程序的一些无法正常工作的代码。

- (void)startConnectionWithURL:(NSString *)feedURL feedList:(NSMutableArray *)list {
self.feedList = list;

// Use NSURLConnection to asynchronously download the data. This means the main thread will not be blocked - the
// application will remain responsive to the user. 
//
// IMPORTANT! The main thread of the application should never be blocked! Also, avoid synchronous network access on any thread.
//
NSURLRequest *feedURLRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:feedURL]];
self.bloggerFeedConnection = [[[NSURLConnection alloc] initWithRequest:feedURLRequest delegate:self] autorelease];

// Test the validity of the connection object. The most likely reason for the connection object to be nil is a malformed
// URL, which is a programmatic error easily detected during development. If the URL is more dynamic, then you should
// implement a more flexible validation technique, and be able to both recover from errors and communicate problems
// to the user in an unobtrusive manner.
NSAssert(self.bloggerFeedConnection != nil, @"Failure to create URL connection.");

// Start the status bar network activity indicator. We'll turn it off when the connection finishes or experiences an error.
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
self.bloggerData = [NSMutableData data];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [bloggerData appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
self.bloggerFeedConnection = nil;
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;   
// Spawn a thread to fetch the link data so that the UI is not blocked while the application parses the XML data.
//
// IMPORTANT! - Don't access UIKit objects on secondary threads.
//
[NSThread detachNewThreadSelector:@selector(parseFeedData:) toTarget:self withObject:bloggerData];
// farkData will be retained by the thread until parseFarkData: has finished executing, so we no longer need
// a reference to it in the main thread.
self.bloggerData = nil;
}

如果您从上到下阅读此内容，您可以看到 NSURLConnection 何时完成我分离一个新线程并调用 parseFeedData。

- (void)parseFeedData:(NSData *)data {
// You must create a autorelease pool for all secondary threads.
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

self.currentParseBatch = [NSMutableArray array];
self.currentParsedCharacterData = [NSMutableString string];
self.feedList = [NSMutableArray array];
//
// It's also possible to have NSXMLParser download the data, by passing it a URL, but this is not desirable
// because it gives less control over the network, particularly in responding to connection errors.
//
NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
[parser setDelegate:self];
[parser parse];

// depending on the total number of links parsed, the last batch might not have been a "full" batch, and thus
// not been part of the regular batch transfer. So, we check the count of the array and, if necessary, send it to the main thread.
if ([self.currentParseBatch count] > 0) {
    [self performSelectorOnMainThread:@selector(addLinksToList:) withObject:self.currentParseBatch waitUntilDone:NO];
}
self.currentParseBatch = nil;
self.currentParsedCharacterData = nil;
[parser release];        
[pool release];
}

在 did 结束元素委托中，我在调用主线程执行更新之前检查是否已解析 5 个项目。

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName {
if ([elementName isEqualToString:kItemElementName]) {
    [self.currentParseBatch addObject:self.currentItem];
    parsedItemsCounter++;
    if (parsedItemsCounter % kSizeOfItemBatch == 0) {
        [self performSelectorOnMainThread:@selector(addLinksToList:) withObject:self.currentParseBatch waitUntilDone:NO];
        self.currentParseBatch = [NSMutableArray array]; 
    }
}  

// Stop accumulating parsed character data. We won't start again until specific elements begin.
accumulatingParsedCharacterData = NO;
}

- (void)addLinksToList:(NSMutableArray *)links {
[self.feedList addObjectsFromArray:links];
// The table needs to be reloaded to reflect the new content of the list.

if (self.viewDelegate != nil && [self.viewDelegate respondsToSelector:@selector(parser:didParseBatch:)]) {
    [self.viewDelegate parser:self didParseBatch:links];
}

}

最后，UIViewController 委托：

- (void)parser:(XMLFeedParser *)parser didParseBatch:(NSMutableArray *)parsedBatch {
NSLog(@"parser:didParseBatch:");
[self.selectedBlogger.feedList addObjectsFromArray:parsedBatch];
[self.tableView reloadData];

}

如果我在视图控制器委托触发以重新加载表时写入日志，并且当 cellForRowAtIndexPath 在重建表时触发时，日志看起来像这样：

parser:didParseBatch:
parser:didParseBatch:
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
parser:didParseBatch:
parser:didParseBatch:
parser:didParseBatch:
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
解析器：didParseBatch：
tableView：cellForRowAtIndexPath
tableView：cellForRowAtIndexPath
tableView：cellForRowAtIndexPath
tableView：cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
解析器:didParseBatch:
解析器:didParseBatch:
解析器:didParseBatch:
解析器:didParseBatch:
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath

显然，当我每次都告诉它时，tableView 并没有重新加载。

正常运行的应用程序的日志如下所示：

parser:didParseBatch:
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
parser:didParseBatch:
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
parser:didParseBatch:
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView: cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
解析器:didParseBatch:
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
解析器:didParseBatch:
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath
tableView:cellForRowAtIndexPath

4

1 回答 1

0

我猜你的数据模型中的某些东西是罪魁祸首。最有可能的是，我认为这会导致节号错误或报告节的行数为零。

一个表在调用之前– numberOfSectionsInTableView:和– tableView:numberOfRowsInSection:之前调用- tableView:cellForRowAtIndexPath。如果他们中的任何一个报告错误的数字，tableview 将假定它没有数据并且什么都不做。

于 2010-01-20T20:36:21.473 回答