为什么UITableView没有重新加载(即使在主线程上)?

时间:2010-01-20 18:47:46

标签: iphone uitableview multithreading nsurlconnection

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。两个程序的设计是使用异步NSURLConnection来获取数据,然后生成一个新线程来处理解析。当解析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工作正常,但在另一个程序中没有。我知道解析实际上是在后台线程上发生的,我知道[tableView reloadData]正在主线程上执行;但是,在完成所有解析之前,它不会重新加载表。我很难过。据我所知......这两个程序的结构完全相同。以下是应用中无法正常工作的一些代码。

- (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,我将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 end元素委托中,我检查在调用主线程执行更新之前已经解析了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重新加载表时写入日志,并且当cellForRowAtIndexPath重建表时触发,那么日志看起来像这样:

解析器:didParseBatch:
解析:didParseBatch:
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
解析:didParseBatch:
解析:didParseBatch:
解析:didParseBatch:
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
解析:didParseBatch:
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
解析:didParseBatch:
解析:didParseBatch:
解析:didParseBatch:
解析:didParseBatch:
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
tableView:cellForRowAtIndexPath

显然,当我每次都告诉它时,tableView没有重新加载。

来自正确运行的应用程序的日志如下所示:

解析器:didParseBatch:
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
解析:didParseBatch:
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
解析:didParseBatch:
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
解析:didParseBatch:
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
解析:didParseBatch:
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
的tableView:的cellForRowAtIndexPath
tableView:cellForRowAtIndexPath

1 个答案:

答案 0 :(得分:0)

我猜你的数据模型中有些东西应该受到指责。最有可能的是,我认为这会导致部分编号错误或报告部分为零行。

在致电– numberOfSectionsInTableView:之前,表格会同时调用– tableView:numberOfRowsInSection:- tableView:cellForRowAtIndexPath。如果其中任何一个报告错误的数字,则表视图将假定它没有数据并且什么都不做。