iPhone：在后台解析多个XML用的NSXMLParser互不干扰 [英] iPhone: Parsing multiple XML with NSXMLParser in background disturbing each other

问题描述

我有一个奇怪的问题，当谈到与的NSXMLParser iPhone上解析XML。当启动应用程序，我想preLOAD 4表视图，由填充的RSS源的背景。

I have a strange issue, when it comes to parsing XML with NSXMLParser on the iPhone. When starting the app, I want to preload 4 table-views, that are populated by RSS-Feeds in the background.

在我的初始化表视图中的一个接一个，比加载，解析和显示像一个魅力的所有的作品。但是，当我尝试一次初始化所有视图（在同一时间），似乎比，即 XML解析器-实例互不干扰的。不知何故，从一个XML的饲料数据，广播到其他的XML解析器的情况下，他们不属于。例如：有一个团队成员项目，以这是我的名字。当这个错误发生时，有一个从添加了另一个XML的饲料，即产生一个字符串：这是我name58，其中58是从另一种观点的东西图表位置。 58似乎再错过另一实例。

When I init the table-views one-by-one, than loading, parsing and displaying all works like a charm. But when I try to init all view at once (at the same time), than it seems, that the XML-parser-instances are disturbing each other. Somehow data from one XML-Feed are "broadcasted" into other xml-parser instances, where they do not belong. Example: there is a "teammember" item, with "This is my name". When this bug occurs, there is a string from another xml-feed added, i.e. resulting in: "This is my name58", where 58 is the chart-position of something from the other view. "58" seems to miss then on the other instance.

在我看来，这个错误发生的原因的NSXMLParser，委托方法：

It looks to me, that this bug occurs because of the NSXMLParser-delegate method:

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
    if (!currentStringValue) {
        currentStringValue = [[NSMutableString alloc] initWithCapacity:50];
    }
    [currentStringValue appendString:string];   
}

在这种情况下，巧合字节附加到字符串，在那里他们不属于

In this case "by coincidence" bytes are appended to strings, where they do not belong to.

但奇怪的是，的NSXMLParser的每个实例都是独一无二的，有自己独特的代表，附加到自己的ViewController。每个解析，请求派生它自己的后台任务，有自己的（也也是独一无二的名字命名）自动释放池。

The strange thing is, that every instance of NSXMLParser is unique, got its own unique delegates, that are attached to their own ViewController. Every parsing-requests spawns it own background-task, with its own (also also unique named) Autorelease-pool.

我打电话的的NSXMLParser这样在ViewController中：

I am calling the NSXMLParser like this in the ViewController:

// prepare XML saving and parsing
currentStringValue = [[[NSMutableString alloc] initWithCapacity:50] retain];    
charts = [[NSMutableArray alloc] init];

NSURL *url = [[NSURL alloc] initWithString:@"http://(SOME XML URL)"];
xmlParser = [[[NSXMLParser alloc] initWithContentsOfURL:url] retain];

//Set delegate
[xmlParser setDelegate:self];

//loading indicator 
progressWheel = [[[UIActivityIndicatorView alloc] initWithFrame:CGRectMake(150.0,170.0,20.0,20.0)] autorelease];
progressWheel.activityIndicatorViewStyle = UIActivityIndicatorViewStyleGray;

[self.view addSubview:progressWheel];
[progressWheel startAnimating];

// start loading and parsing the xml-feed in the background
//[self performSelectorInBackground:@selector(parse:) withObject:xmlParser]; -> I also tried this
[NSThread detachNewThreadSelector:@selector(parse:) toTarget:self withObject:xmlParser];

这是背景，任务之一，解析饲料：

And this is one of the background-tasks, parsing the feed:

- （无效）解析：（*的NSXMLParser）myParser {

-(void)parse:(NSXMLParser*)myParser {

NSAutoreleasePool *schedulePool = [[NSAutoreleasePool alloc] init];

BOOL success = [myParser parse];

if(success) {
    NSLog(@"No Errors. xmlParser got: %@", myParser);

    (POST-PROCESSING DETAILS OF THE DATA RETURNED)

    [self.tableView reloadData];            

} else {    
    NSLog(@"Couldn't initalize XMLparser");
}

[progressWheel stopAnimating];

[schedulePool drain];

[myParser release]; 

}

这是什么原因这个问题？难道我打电话以正确的方式在后台任务？为什么这个bug接近，因为每个XML解析器有自己的独特的实例？

What could cause this issue? Am I calling the background-task in the right way? Why is this bug approaching, since every XML-Parser got its own, unique instance?

推荐答案

您不应该更新从后台线程中的UI元素（如 progressWheel ）。 UI更新应该在主线程中完成。

You should not be updating UI elements (like progressWheel) from inside a background thread. UI updates should be done on the main thread.

使用 -performSelectorOnMainThread：withObject：waitUntilDone：来从后台线程中更新UI元素

Use -performSelectorOnMainThread:withObject:waitUntilDone: to update UI elements from within a background thread.

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