我正在尝试使用传入的图像更新单元格。 我有一个协议，当图像下载完成时调用相应的方法。 UITable的源是对象“Meeting”的NSArray。 每个Meeting都持有其表格单元格的indexPath，我在其中获取 -
(UITableViewCell *)tableView:(UITableView *)_tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
Meeting * meeting = [tableDataSource objectAtIndex:indexPath.row];
... cell's init code
meeting.cellPath = indexPath; // also tried [indexPath copy];
...
}
问题是，当我尝试使用存储的IndexPath更新单元格时，我遇到了一个奇怪的错误，提示我有一个我没有的NSMutable数组：
2012-07-20 20:15:18.007 MyNewbieApp[5734:207] meeting.cellPath = [row = 2,section = 0]
2012-07-20 20:15:18.705 MyNewbieApp[5734:207] meeting.cellPath = [row = 4,section = 0]
2012-07-20 20:15:18.728 MyNewbieApp[5734:207] meeting.cellPath = [row = 5,section = 0]
2012-07-20 20:15:18.730 MyNewbieApp[5734:207] downloadDidFinishDownloading <NSIndexPath 0x79456f0> 2 indexes [0, 5]
2012-07-20 20:15:18.732 MyNewbieApp[5734:207] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSMutableArray objectAtIndex:]: index 3 beyond bounds [0 .. 2]'
*** Call stack at first throw:
(
0 CoreFoundation 0x02c70b99 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x02a6540e objc_exception_throw + 47
2 CoreFoundation 0x02c66695 -[__NSArrayM objectAtIndex:] + 261
3 UIKit 0x00556327 -[_UITableViewUpdateSupport(Private) _setupAnimationsForExistingVisibleCells] + 264
4 UIKit 0x00555b9b -[_UITableViewUpdateSupport initWithTableView:updateItems:oldRowData:newRowData:oldRowRange:newRowRange:context:] + 436
5 UIKit 0x003ab5d6 -[UITableView(_UITableViewPrivate) _updateWithItems:withOldRowData:oldRowRange:newRowRange:context:] + 1323
6 UIKit 0x003a7f03 -[UITableView(_UITableViewPrivate) _endCellAnimationsWithContext:] + 9179
7 UIKit 0x003974d3 -[UITableView reloadRowsAtIndexPaths:withRowAnimation:] + 56
8 MyNewbieApp 0x00017354 -[MeetingsVC downloadDidFinishDownloading:] + 174
9 MyNewbieApp 0x000173a6 -[MeetingsVC download:didFailWithError:] + 43
10 MyNewbieApp 0x00010e5f -[Meeting image] + 317
11 MyNewbieApp 0x00016f49 -[MeetingsVC tableView:cellForRowAtIndexPath:] + 2141
12 UIKit 0x0039ed6f -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:withIndexPath:] + 619
13 UIKit 0x00394e02 -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:] + 75
14 UIKit 0x003a9774 -[UITableView(_UITableViewPrivate) _updateVisibleCellsNow:] + 1561
15 UIKit 0x003a17ec -[UITableView layoutSubviews] + 242
16 QuartzCore 0x02619481 -[CALayer layoutSublayers] + 177
17 QuartzCore 0x026191b1 CALayerLayoutIfNeeded + 220
18 QuartzCore 0x026122e0 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 302
19 QuartzCore 0x02612040 _ZN2CA11Transaction6commitEv + 292
20 QuartzCore 0x02642ebb _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 99
21 CoreFoundation 0x02c51f4b __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 27
22 CoreFoundation 0x02be6b27 __CFRunLoopDoObservers + 295
23 CoreFoundation 0x02bafce7 __CFRunLoopRun + 1575
24 CoreFoundation 0x02baf350 CFRunLoopRunSpecific + 208
25 CoreFoundation 0x02baf271 CFRunLoopRunInMode + 97
26 GraphicsServices 0x0318000c GSEventRunModal + 217
27 GraphicsServices 0x031800d1 GSEventRun + 115
28 UIKit 0x0033baf2 UIApplicationMain + 1160
29 MyNewbieApp 0x00002034 main + 102
30 MyNewbieApp 0x00001fc5 start + 53
)
terminate called after throwing an instance of 'NSException'
所以它是索引数组越界异常。但我没有任何有3个元素的NSMutableArray。我所有的数组都要大得多。啊，异常是从这里出来的：
- (void)downloadDidFinishDownloading:(Meeting *)meeting
{
NSLog(@"downloadDidFinishDownloading %@",meeting.cellPath);
//NSLog(@"downloadDidFinishDownloading meeting.cellPath = [row = %d,section = %d]",meeting.cellPath.row,meeting.cellPath.section);
[self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:meeting.cellPath] withRowAnimation:UITableViewRowAnimationNone];
meeting.delegate = nil;
}
- (void)download:(Meeting *)meeting didFailWithError:(NSError *)error{
[self downloadDidFinishDownloading:meeting];
}
这个回调方法会在每次会议图片下载完成后被调用。如果我注释掉reloadRowsAtIndexPaths这行代码，一切都正常。否则就会出错。这到底是什么原因呢？我花了很多时间但毫无结果...我真的不知道这是怎么回事...更奇怪的是，问题总是出现在第五个元素上:)当我向上滚动表格内容时。而第五个元素并没有什么特别之处，我已经尝试了另一个数据集，但问题仍然存在。
更新：只有当代码调用
download:(Meeting*)meeting didFailWithError方法时才会发生错误/崩溃。但它仍然有相同的meeting参数，我发送给downloadDidFinishDownloading。我也尝试了以下方法： - (void)download:(Meeting *)meeting didFailWithError:(NSError *)error{
[self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:meeting.cellPath] withRowAnimation:UITableViewRowAnimationNone];
meeting.delegate = nil;
}
现在应用程序只会在reloadRowsAtIndexPaths方法中崩溃。