超出空数组崩溃范围的索引'5'

Question

我正在构建一个RSS阅读器，并在导航栏的右角放置一个刷新按钮。它运行良好，我没有撞车事故。但如果我在滚动时按下刷新按钮，应用程序就会崩溃。我不知道问题出在哪里。我分析了这个项目，但找不到任何东西。。。

所以我得到的错误是：

2012-01-22 16:36:48.205 GYSA[712:707] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 5 beyond bounds for empty array'
*** First throw call stack:
(0x37adb8bf 0x315c11e5 0x37a24b6b 0x7913 0x34ef39cb 0x34ef2aa9 0x34ef2233 0x34e96d4b 0x37a3a22b 0x33231381 0x33230f99 0x3323511b 0x33234e57 0x3325c6f1 0x3327f4c5 0x3327f379 0x37249f93 0x3747b891 0x37aa4f43 0x37aaf553 0x37aaf4f5 0x37aae343 0x37a314dd 0x37a313a5 0x375affcd 0x34ec1743 0x2ac9 0x2a54)
terminate called throwing an exception(gdb)

这是我的代码：

#import "RssFunViewController.h"
#import "BlogRssParser.h"
#import "BlogRss.h"
@implementation RssFunViewController
@synthesize rssParser = _rssParser;
@synthesize tableView = _tableView;
@synthesize appDelegate = _appDelegate;
@synthesize toolbar = _toolbar;
-(void)toolbarInit{
    UIBarButtonItem *refreshButton = [[UIBarButtonItem alloc]
                                   initWithBarButtonSystemItem:UIBarButtonSystemItemRefresh
                                   target:self action:@selector(reloadRss)];
    refreshButton.enabled = YES;
    self.navigationItem.rightBarButtonItem = refreshButton;
    [refreshButton release];
    UIImage *image = [UIImage imageNamed: @"navigationbar.png"];
    UIImageView *imageview = [[UIImageView alloc] initWithImage: image];
    UIBarButtonItem *button = [[UIBarButtonItem alloc] initWithCustomView: imageview];
    self.navigationItem.leftBarButtonItem = button;
    [imageview release];
    [button release];
}

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.autoresizesSubviews = YES;
    self.view.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    [self toolbarInit];
    _rssParser = [[BlogRssParser alloc]init];
    self.rssParser.delegate = self;
    [[self rssParser]startProcess];
}
-(void)reloadRss{
    [self toggleToolBarButtons:NO];
    [[self rssParser]startProcess];
}
-(void)toggleToolBarButtons:(BOOL)newState{
    NSArray *toolbarItems = self.toolbar.items;
    for (UIBarButtonItem *item in toolbarItems){
        item.enabled = newState;
    }   
}
//Delegate method for blog parser will get fired when the process is completed
- (void)processCompleted{
    //reload the table view
    [self toggleToolBarButtons:YES];
    [[self tableView]reloadData];
}
-(void)processHasErrors{
    //Might be due to Internet
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Achtung!" message:@"Leider ist es im Moment nicht möglich eine Verbindung zum Internet herzustellen. Ohne Internetverbindung ist die App nur in beschränktem Umfang nutzbar!"
                                                   delegate:nil cancelButtonTitle:@"OK" otherButtonTitles: nil];
    [alert show];   
    [alert release];
    [self toggleToolBarButtons:YES];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
    return [[[self rssParser]rssItems]count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:@"rssItemCell"];
    if(nil == cell){
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"rssItemCell"]autorelease];
    }
    cell.textLabel.text = [[[[self rssParser]rssItems]objectAtIndex:indexPath.row]title];
    cell.detailTextLabel.text = [[[[self rssParser]rssItems]objectAtIndex:indexPath.row]description];
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    return cell;
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    [[self appDelegate] setCurrentlySelectedBlogItem:[[[self rssParser]rssItems]objectAtIndex:indexPath.row]];
    [self.appDelegate loadNewsDetails];
    [_tableView deselectRowAtIndexPath:indexPath animated: YES];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}
- (void)dealloc {
    [_appDelegate release];
    [_toolbar release];
    [_tableView release];
    [_rssParser release];
    [super dealloc];
}
@end

我找到了导致问题的代码行：

cell.textLabel.text = [[[[self rssParser]rssItems]objectAtIndex:indexPath.row]title];
cell.detailTextLabel.text = [[[[self rssParser]rssItems]objectAtIndex:indexPath.row]description];

如果我删除这些代码行，我就无法重现错误。但正如你所能想象的，它们对于RSS提要来说是必要的：）。

有什么解决方案吗？

这是提取代码：

#import "BlogRssParser.h"
#import "BlogRss.h"
@implementation BlogRssParser
@synthesize currentItem = _currentItem;
@synthesize currentItemValue = _currentItemValue;
@synthesize rssItems = _rssItems;
@synthesize delegate = _delegate;
@synthesize retrieverQueue = _retrieverQueue;

- (id)init{
    self = [super init];
    if(self){
        _rssItems = [[NSMutableArray alloc]init];
    }
    return self;
}
- (NSOperationQueue *)retrieverQueue {
    if(nil == _retrieverQueue) {
        _retrieverQueue = [[NSOperationQueue alloc] init];
        _retrieverQueue.maxConcurrentOperationCount = 1;
    }
    return _retrieverQueue;
}
- (void)startProcess{
    SEL method = @selector(fetchAndParseRss);
    [[self rssItems] removeAllObjects];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self 
                                                                     selector:method 
                                                                       object:nil];
    [self.retrieverQueue addOperation:op];
    [op release];
}
-(BOOL)fetchAndParseRss{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
    //To suppress the leak in NSXMLParser
    [[NSURLCache sharedURLCache] setMemoryCapacity:0];
    [[NSURLCache sharedURLCache] setDiskCapacity:0];
    BOOL success = NO;
    NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:url];
    [parser setDelegate:self];
    [parser setShouldProcessNamespaces:YES];
    [parser setShouldReportNamespacePrefixes:YES];
    [parser setShouldResolveExternalEntities:NO];
    success = [parser parse];
    [parser release];
    [pool drain];
    return success;
}
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI 
 qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict{
    if(nil != qualifiedName){
        elementName = qualifiedName;
    }
    if ([elementName isEqualToString:@"item"]) {
        self.currentItem = [[[BlogRss alloc]init]autorelease];
    }else if ([elementName isEqualToString:@"media:thumbnail"]) {
        self.currentItem.mediaUrl = [attributeDict valueForKey:@"url"];
    } else if([elementName isEqualToString:@"title"] || 
              [elementName isEqualToString:@"description"] ||
              [elementName isEqualToString:@"link"] ||
              [elementName isEqualToString:@"guid"] ||
              [elementName isEqualToString:@"pubDate"]) {
        self.currentItemValue = [NSMutableString string];
    } else {
        self.currentItemValue = nil;
    }   
}
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName {
    if(nil != qName){
        elementName = qName;
    }
    if([elementName isEqualToString:@"title"]){
        self.currentItem.title = self.currentItemValue;
    }else if([elementName isEqualToString:@"description"]){
        self.currentItem.description = self.currentItemValue;
    }else if([elementName isEqualToString:@"link"]){
        self.currentItem.linkUrl = self.currentItemValue;
    }else if([elementName isEqualToString:@"guid"]){
        self.currentItem.guidUrl = self.currentItemValue;
    }else if([elementName isEqualToString:@"pubDate"]){
        NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
        [formatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss'Z'"];
        self.currentItem.pubDate = [formatter dateFromString:self.currentItemValue];
        [formatter release];
    }else if([elementName isEqualToString:@"item"]){
        [[self rssItems] addObject:self.currentItem];
    }
}
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
    if(nil != self.currentItemValue){
        [self.currentItemValue appendString:string];
    }
}
- (void)parser:(NSXMLParser *)parser foundCDATA:(NSData *)CDATABlock{
    //Not needed for now
}
- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError{
    if(parseError.code != NSXMLParserDelegateAbortedParseError) {
        [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
        [(id)[self delegate] performSelectorOnMainThread:@selector(processHasErrors)
         withObject:nil
         waitUntilDone:NO];
    }
}

- (void)parserDidEndDocument:(NSXMLParser *)parser {
    [(id)[self delegate] performSelectorOnMainThread:@selector(processCompleted)
     withObject:nil
     waitUntilDone:NO];
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}

-(void)dealloc{
    self.currentItem = nil;
    self.currentItemValue = nil;
    self.delegate = nil;
    [_rssItems release];
    [super dealloc];
}
@end

Answer 1

您应该做的是将提取的数据数组复制到ivar中。然后从该ivar填充表视图，然后在processCompleted中将新数据复制到ivar并调用reloadData。这将防止表视图处于您正在经历的不一致状态。

@property (retain, nonatomic) NSArray *sourceArray;
- (void)processCompleted{
    self.sourceArray = [[[[self rssParser]rssItems] copy] autorelease];
    [self toggleToolBarButtons:YES];
    [[self tableView]reloadData];
}

然后在填充表视图时引用复制的数组。例如：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:@"rssItemCell"];
    if(nil == cell){
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"rssItemCell"]autorelease];
    }
    cell.textLabel.text = [[self.sourceArray objectAtIndex:indexPath.row]title];
    cell.detailTextLabel.text = [[self.sourceArray objectAtIndex:indexPath.row]description];
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    return cell;
}

类似地，在引用[[self rssParser]rssItems]的其他表视图委托方法中也是如此。

Answer 2

可能是在滚动和刷新的同时，数据源在被填充之前就被清空了。因此，虽然您的表视图认为它有5行，但您的数据源没有5项，因为您是从源所在的位置下载它们的。当它查询第五项时，那里什么都没有，您的应用程序就会崩溃。

编辑

我是对的。刷新代码调用startProcess，它清空用于填充数组的数组，然后一次向其中添加一个项，并且在后台队列中执行此操作，因此它可能是异步的。

解决方案是将新项目写入后台队列中的一个中间数组，当过程完成时，用该数组替换当前rssItems，并重新加载表视图。

Answer 3

重新加载表视图时进行检查。当您滚动重新加载时，会自动调用tableview。因此，在将数组的内容分配给单元格之前，请检查数组中是否有值。检查数组计数是否大于0，然后写入这些行。

Answer 4

在我的例子中，在调用刷新的方法的开头添加这行代码是有效的：

tableView.scrollEnabled = NO;

当然，你需要在最后再次设置你的表视图：

tableView.scrollEnabled = YES;