objective-c - 执行 NSMutableArray 后出现错误

Question

这是代码。我尝试创建一个包含名称、大小和图像(从资源获取)的对象，然后将该对象添加到 NSMutableArray 中，以便在 NSTableView 中显示这些对象。但是，在运行代码后，我确实获得了 NSMutableArray 中对象的正确计数以及每个对象中的正确信息(名称、大小、图像)，但它仍然给我错误。你们能帮帮我吗？我是一名新的 Mac 开发人员。谢谢!!

这是代码:

    @implementation AppDelegate{
        NSMutableArray* _tableContents;
    }

   -(void)awakeFromNib{

        NSString* imagePath = @"USB.png";
        NSString* mountPath = @"/Volumes";

       _tableContents = [[NSMutableArray alloc]init];

      for(mountPath in [[NSWorkspace sharedWorkspace]mountedLocalVolumePaths])
      {
        if(0==[mountPath rangeOfString:@"/Volumes/"].location)
        {            

           NSString* USBpath = [[[NSWorkspace sharedWorkspace]mountedLocalVolumePaths]objectAtIndex:count];

           //get the name of USB drive
           NSString* nameOfUSB = [USBpath substringFromIndex:9];

          //get the size of USB drive
          NSNumber *volumeSize;
          NSURL *mountPathPicked = [NSURL fileURLWithPath:mountPath];

          if([mountPathPicked getResourceValue:&volumeSize forKey:NSURLVolumeTotalCapacityKey error:nil])
          {
            NSDictionary *obj = @{@"name":nameOfUSB,
                                  @"image":[NSImage imageNamed:imagePath],
                                  @"size":volumeSize
                                  };

            //after I call the following line, it will give me error !!
            [_tableContents addObject:obj];
          }
       }
        count ++;
      }
    }

//I also use the following two methods in order to show the name, and image in NSTableView
-(NSInteger)numberOfRowsInTableView:(NSTableView *)tableView{
    return [_tableCountents count];
}

-(NSView *)tableView:(NSTableView *)tableView viewForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row{

  NSDictionary *flag = _tableContents[row];
  NSString *identifier = [tableColumn identifier];//call different col we need identifier
  if([identifier isEqualToString:@"MainCell"])
  {
      NSTableCellView *cellView = [tableView makeViewWithIdentifier:@"MainCell" owner:self];//give back specific cell named mainCell
      [cellView.textField setStringValue:flag[@"name"]];
      [cellView.imageView setImage:flag[@"image"]];
      return cellView;
  }
  return nil;
}

GUI 中没有连接问题。这是错误消息:

2013-04-25 01:16:41.321 NAMEOFPROJECT[8243:303] An uncaught exception was raised
2013-04-25 01:16:41.322 NAMEOFPROJECT[8243:303] *** -[__NSArrayI objectAtIndex:]: index 7 beyond bounds [0 .. 3]
2013-04-25 01:16:41.329 NAMEOFPROJECT[8243:303] (
0   CoreFoundation                      0x00007fff9147cb06 __exceptionPreprocess + 198
1   libobjc.A.dylib                     0x00007fff900c03f0 objc_exception_throw + 43
2   CoreFoundation                      0x00007fff9142fb53 -[__NSArrayI objectAtIndex:] + 163
3   CDTOANYDRIVE                        0x00000001000011d6 -[AppDelegate DetectingUSBDrives] + 710
4   CDTOANYDRIVE                        0x0000000100000efb -[AppDelegate awakeFromNib] + 43
5   AppKit                              0x00007fff899631a8 -[NSIBObjectData nibInstantiateWithOwner:topLevelObjects:] + 1234
6   AppKit                              0x00007fff89b79976 -[NSNib _instantiateNibWithExternalNameTable:] + 610
7   AppKit                              0x00007fff89b7a41a -[NSNib instantiateNibWithExternalNameTable:] + 17
8   AppKit                              0x00007fff89b262b4 -[NSTableRowData _unarchiveViewWithIdentifier:owner:] + 520
9   CDTOANYDRIVE                        0x000000010000174b -[AppDelegate tableView:viewForTableColumn:row:] + 219
10  AppKit                              0x00007fff89b279a2 -[NSTableRowData _addViewToRowView:atColumn:row:] + 324
11  AppKit                              0x00007fff89b2766f -[NSTableRowData _addViewsToRowView:atRow:] + 151
12  AppKit                              0x00007fff89b25c05 -[NSTableRowData _addRowViewForVisibleRow:withPriorView:] + 415
13  AppKit                              0x00007fff89b2598a -[NSTableRowData _addRowViewForVisibleRow:withPriorRowIndex:inDictionary:withRowAnimation:] + 272
14  AppKit                              0x00007fff89b24c59 -[NSTableRowData _unsafeUpdateVisibleRowEntries] + 740
15  AppKit                              0x00007fff89b247f1 -[NSTableRowData updateVisibleRowViews] + 119
16  AppKit                              0x00007fff89afc5d7 -[NSTableView layout] + 165
17  AppKit                              0x00007fff89aafe95 -[NSView _layoutSubtreeHeedingRecursionGuard:] + 112
18  CoreFoundation                      0x00007fff914754a6 __NSArrayEnumerate + 582
19  AppKit                              0x00007fff89aafff6 -[NSView _layoutSubtreeHeedingRecursionGuard:] + 465
20  CoreFoundation                      0x00007fff914754a6 __NSArrayEnumerate + 582
21  AppKit                              0x00007fff89aafff6 -[NSView _layoutSubtreeHeedingRecursionGuard:] + 465
22  CoreFoundation                      0x00007fff914754a6 __NSArrayEnumerate + 582
23  AppKit                              0x00007fff89aafff6 -[NSView _layoutSubtreeHeedingRecursionGuard:] + 465
24  CoreFoundation                      0x00007fff914754a6 __NSArrayEnumerate + 582
25  AppKit                              0x00007fff89aafff6 -[NSView _layoutSubtreeHeedingRecursionGuard:] + 465
26  AppKit                              0x00007fff89aafd2e -[NSView layoutSubtreeIfNeeded] + 615
27  AppKit                              0x00007fff89aab4dc -[NSWindow(NSConstraintBasedLayout) layoutIfNeeded] + 201
28  AppKit                              0x00007fff899d96a8 -[NSView _layoutAtWindowLevelIfNeeded] + 99
29  AppKit                              0x00007fff899d8fe6 -[NSView _sendViewWillDrawInRect:clipRootView:] + 87
30  AppKit                              0x00007fff899a59b1 -[NSView displayIfNeeded] + 1044
31  AppKit                              0x00007fff89a62a48 -[NSWindow _reallyDoOrderWindow:relativeTo:findKey:forCounter:force:isModal:] + 1377
32  AppKit                              0x00007fff89a62068 -[NSWindow _doOrderWindow:relativeTo:findKey:forCounter:force:isModal:] + 940
33  AppKit                              0x00007fff89a61c4f -[NSWindow orderWindow:relativeTo:] + 159
34  AppKit                              0x00007fff89963266 -[NSIBObjectData nibInstantiateWithOwner:topLevelObjects:] + 1424
35  AppKit                              0x00007fff8994214d loadNib + 317
36  AppKit                              0x00007fff89941679 +[NSBundle(NSNibLoading) _loadNibFile:nameTable:withZone:ownerBundle:] + 219
37  AppKit                              0x00007fff899414ae -[NSBundle(NSNibLoading) loadNibNamed:owner:topLevelObjects:] + 200
38  AppKit                              0x00007fff8994128e +[NSBundle(NSNibLoading) loadNibNamed:owner:] + 360
39  AppKit                              0x00007fff8993da2f NSApplicationMain + 398
40  CDTOANYDRIVE                        0x0000000100000e82 main + 34
41  libdyld.dylib                       0x00007fff9385a7e1 start + 0
42  ???                                 0x0000000000000003 0x0 + 3
)

上面的错误显示两次!!

Answer 1

我已经在迷你应用程序中尝试过你的代码，它工作正常。我可能会强调以下几点:

1. 您的异常发生在 DetectingUSBDrives 方法中，我们没有任何代码。我假设您已将代码粘贴到 awakeFromNib 方法中。
2. 您正在使用 count 作为索引。该变量是否初始化为零？
3. 错误出现两次的事实表明您的单元格 View 持有对应用程序委托(delegate)的引用，这意味着每次创建 View 时都会调用 awakeFromNib 一次。这可能会产生很多问题，因为您正在那里初始化 _tableOfContents 。您可能希望将所有代码移至 init 方法。