-[User length]: unrecognized selector sent to instance 0x7fc7b60143e0' - ios

Question

I have the following code and receive the error code indicated in title:
This is the only messages i send to User object (other than initialising it by using "new")
When I out comment addObject: it doesn't complain.
Can anybody help? Thanks!
self.freshUser.name = self.name.text;
self.freshUser.age = (int)self.age.text;
self.freshUser.gender = self.gender.text;
//NSLog(#"%#",[NSThread callStackSymbols]);
[appDelegate.users addObject:self.freshUser];
(My user object subclasses NSObject. it has more property that I don't use. just a little extra info)
-(UITableViewCell *)tableView:(UITableView *)tableViewPara cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UserCell *cell = [tableViewPara dequeueReusableCellWithIdentifier:usersTableIdentifier forIndexPath:indexPath];
if(indexPath.row == [appDelegate.users count]){
cell.nameLabel.text = #"+";
cell.nameLabel.font = [UIFont systemFontOfSize:36];
cell.bgImg.image = [UIImage imageNamed:#"background_gray"];
cell.statusImg.image = nil;
}else{
cell.nameLabel.text = appDelegate.users[indexPath.row];
cell.nameLabel.font = [UIFont systemFontOfSize:17];
cell.bgImg.image = [UIImage imageNamed:#"background_dark_red"];
cell.statusImg.image = [UIImage imageNamed:#"icon_cloud"];
}
cell.nameLabel.textAlignment = NSTextAlignmentCenter;
cell.nameLabel.textColor = [UIColor whiteColor];
cell.nameLabel.backgroundColor = [UIColor clearColor];
return cell;
}
space
0 CoreFoundation 0x000000010ff1bf35 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x000000010fbb4bb7 objc_exception_throw + 45
2 CoreFoundation 0x000000010ff2304d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3 CoreFoundation 0x000000010fe7b27c ___forwarding___ + 988
4 CoreFoundation 0x000000010fe7ae18 _CF_forwarding_prep_0 + 120
5 UIKit 0x00000001104d034b -[UILabel _setFont:] + 101
6 Raymio 0x000000010f67857f -[StartViewController tableView:cellForRowAtIndexPath:] + 991
7 UIKit 0x00000001103ff4b3 -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] + 508
8 UIKit 0x00000001103defb1 -[UITableView _updateVisibleCellsNow:isRecursive:] + 2846
9 UIKit 0x00000001103f4e3c -[UITableView layoutSubviews] + 213
10 UIKit 0x0000000110381973 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 521
11 QuartzCore 0x0000000113c09de8 -[CALayer layoutSublayers] + 150
12 QuartzCore 0x0000000113bfea0e _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 380
13 QuartzCore 0x0000000113bfe87e _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24
14 QuartzCore 0x0000000113b6c63e _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 242
15 QuartzCore 0x0000000113b6d74a _ZN2CA11Transaction6commitEv + 390
16 QuartzCore 0x0000000113b6ddb5 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 89
17 CoreFoundation 0x000000010fe50dc7 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
18 CoreFoundation 0x000000010fe50d20 __CFRunLoopDoObservers + 368
19 CoreFoundation 0x000000010fe46b53 __CFRunLoopRun + 1123
20 CoreFoundation 0x000000010fe46486 CFRunLoopRunSpecific + 470
21 GraphicsServices 0x00000001134fd9f0 GSEventRunModal + 161
22 UIKit 0x0000000110308420 UIApplicationMain + 1282
23 Raymio 0x000000010f678a83 main + 115
24 libdyld.dylib 0x00000001124ab145 start + 1

Answer 1

This line:
cell.nameLabel.text = appDelegate.users[indexPath.row];
You're trying to set a User object to the text of a label field. That's not going to work. You'll want this or something close:
cell.nameLabel.text = ((User *)appDelegate.users[indexPath.row]).name;

Answer 2

You shared your stack trace with us. A useful technique is to look in it for anything that references code you wrote. You may notice that line 6 references your StartViewController:
6 Raymio 0x000000010f67857f -[StartViewController tableView:cellForRowAtIndexPath:] + 991
You can show the relevant line of code by typing source list command using that address in the third column:
(lldb) source list -a 0x000000010f67857f
43 cell.nameLabel.text = #"+";
44 cell.nameLabel.font = [UIFont systemFontOfSize:36];
45 cell.bgImg.image = [UIImage imageNamed:#"background_gray"];
46 cell.statusImg.image = nil;
47 }else{
-> 48 cell.nameLabel.text = appDelegate.users[indexPath.row];
49 cell.nameLabel.font = [UIFont systemFontOfSize:17];
50 cell.bgImg.image = [UIImage imageNamed:#"background_dark_red"];
51 cell.statusImg.image = [UIImage imageNamed:#"icon_cloud"];
52 }
Clearly your line numbers and memory addresses will vary, but hopefully this will illustrate the idea. Scan the stack trace for anything that references your code, and examine that line of code for any potential issues.
By the way, this discussion. also shows you how to use the -[StartViewController tableView:cellForRowAtIndexPath:] + 991 of the stack trace to show the relevant line of code.