Cannot change UIView background colour - ios

Question

I have an iOS app which contains a UIView and a sub UIView in my ViewController. (Created in Storyboard).
I want to change the background colour of the subview in an IBAction but the app just crashes. Here is my code:
-(IBAction)open_popup {
[popupView setBackgroundColor:[UIColor colorWithRed:0 green:255 blue:0 alpha:1.0]];
}
Update - This is how I have declared the popup view
IBOutlet UIView *popupView; // in my header file
Update - Here is the error I am getting
2014-08-02 18:20:39.009 ZenApp[1373:60b] 4
2014-08-02 18:20:39.011 ZenApp[1373:60b] -[NSCFType CGColor]: unrecognized selector sent to instance 0x10c896a60
2014-08-02 18:20:39.015 ZenApp[1373:60b] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFType CGColor]: unrecognized selector sent to instance 0x10c896a60' *
First throw call stack: (
0 CoreFoundation 0x0000000101f05495 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x0000000101c6499e objc_exception_throw + 43
2 CoreFoundation 0x0000000101f9665d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3 CoreFoundation 0x0000000101ef6d8d ___forwarding_ + 973
4 CoreFoundation 0x0000000101ef6938 _CF_forwarding_prep_0 + 120
5 UIKit 0x000000010086466c -[UIView(Hierarchy) _setBackgroundColor:] + 37
6 ZenApp 0x00000001000036f8 -[ViewController change_colour_stage_4] + 168
7 ZenApp 0x0000000100002e5d -[ViewController change_colours] + 205
8 ZenApp 0x00000001000030db -[ViewController change_colour_stage_1] + 587
9 ZenApp 0x0000000100002d17 -[ViewController viewDidLoad] + 3079
10 UIKit 0x000000010090759e -[UIViewController loadViewIfRequired] + 562
11 UIKit 0x0000000100907777 -[UIViewController view] + 29
12 UIKit 0x00000001008502d2 -[UIWindow handleStatusBarChangeFromHeight:toHeight:] + 530
13 UIKit 0x0000000100851ca6 +[UIWindow _noteStatusBarHeightChanged:oldHeight:forAutolayoutRootViewsOnly:] + 230
14 UIKit 0x000000010086a92f +[UIView(UIViewAnimationWithBlocks) _setupAnimationWithDuration:delay:view:options:factory:animations:start:animationStateGenerator:completion:] + 460
15 UIKit 0x000000010086abc5 +[UIView(UIViewAnimationWithBlocks) animateWithDuration:animations:completion:] + 59
16 UIKit 0x0000000100813bf5 -[UIApplication _setStatusBarHidden:animationParameters:changeApplicationFlag:] + 478
17 UIKit 0x0000000100847c33 -[UIWindow _setHidden:forced:] + 221
18 UIKit 0x0000000100850ffa -[UIWindow makeKeyAndVisible] + 51
19 UIKit 0x000000010080cc98 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1788
20 UIKit 0x0000000100810a0c -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 660
21 UIKit 0x0000000100821d4c -[UIApplication handleEvent:withNewEvent:] + 3189
22 UIKit 0x0000000100822216 -[UIApplication sendEvent:] + 79
23 UIKit 0x0000000100812086 _UIApplicationHandleEvent + 578
24 GraphicsServices 0x000000010386671a _PurpleEventCallback + 762
25 GraphicsServices 0x00000001038661e1 PurpleEventCallback + 35
26 CoreFoundation 0x0000000101e87679 CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION + 41
27 CoreFoundation 0x0000000101e8744e __CFRunLoopDoSource1 + 478
28 CoreFoundation 0x0000000101eb0903 __CFRunLoopRun + 1939
29 CoreFoundation 0x0000000101eafd83 CFRunLoopRunSpecific + 467
30 UIKit 0x00000001008102e1 -[UIApplication _run] + 609
31 UIKit 0x0000000100811e33 UIApplicationMain + 1010
32 ZenApp 0x0000000100004413 main + 115
33 libdyld.dylib 0x00000001034e65fd start + 1
34 ??? 0x0000000000000001 0x0 + 1 )
libc++abi.dylib: terminating with uncaught exception of type NSException (lldb)
Thanks for your time, Dan.

Answer 1

Your stack trace shows this:
2 CoreFoundation 0x0000000101f9665d -[NSObject(NSObject)
doesNotRecognizeSelector:] + 205 3 CoreFoundation 0x0000000101ef6d8d
___forwarding_ + 973 4 CoreFoundation 0x0000000101ef6938 _CF_forwarding_prep_0 + 120 5 UIKit 0x000000010086466c -[UIView(Hierarchy) _setBackgroundColor:] + 37
Which means popupView has no idea what setBackgroundColor is. (doesNotRecognizeSelector)
Check and make sure that popupView is actually a valid UIView object.

Answer 2

Ok well I tried #Tander solution but then Xcode suggested I access the UIView like this: "->" and then it worked.... I'm not sure why though. If anyone knows, I would be grateful if you could explain why it works this way.
Old code:
[popupView setBackgroundColor:[UIColor colorWithRed:0.0f/255.0f green:255/255 blue:0/255 alpha:1.0]];
New code:
[self->popupView setBackgroundColor:[UIColor colorWithRed:0.0f/255.0f green:255/255 blue:0/255 alpha:1.0]];
This did the trick.

Answer 3

Even you can set the image as background as shown below:
For color
popupView.backgroundColor = [UIColor colorWithRed:0 green:255 blue:0 alpha:1.0];
For set the Image as background:
popupView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:#"ImageName.png"]];