objective c - xcode 6 IB_DESIGNABLE- not loading resources from bundle in Interface builder

Question

I am trying to make a custom control that updates live in Interface Builder using the new IB_DESIGNABLE option described here.

- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();

CGRect myFrame = self.bounds;
CGContextSetLineWidth(context, 10);
CGRectInset(myFrame, 5,5);
[[UIColor redColor] set];
UIRectFrame(myFrame);

NSBundle *bundle = [NSBundle mainBundle];
NSString *plistPath;

plistPath = [bundle pathForResource:@"fileExample" ofType:@"plist"];
UIImage *tsliderOff = [UIImage imageNamed:@"btn_slider_off.png"];

[tsliderOff drawInRect:self.bounds];
}

When I run in the simulator, I get a red box with my image in the center (as expected):

But when I try use the Interface Builder, it only shows up as a red box (no image in the middle):

When I debug it: Editor->Debug Selected Views, it reveals that anything loaded from the bundle is nil. The plistPath and tsliderOff both appear as nil.

I made sure that btn_slider_off.png was included in the Targets->myFrameWork->Build Phases->Copy Bundle Resources.

Any idea why Interface Builder doesn't see the png file during editing, but shows ok when running? "Creating a Custom View that Renders in Interface Builder" is a little limited if I can't load any images to render...

---

edit based on solution by rickster

rickster pointed me to the solution - the problem is that the files don't live in mainBundle, they live in [NSBundle bundleForClass:[self class]]; And it appears that [UIImage imageNamed:@"btn_slider_off.png"] automatically uses mainBundle.

The following code works!

#if !TARGET_INTERFACE_BUILDER
NSBundle *bundle = [NSBundle mainBundle];
#else
NSBundle *bundle = [NSBundle bundleForClass:[self class]];
#endif
NSString *fileName = [bundle pathForResource:@"btn_slider_off" ofType:@"png"];
UIImage *image = [UIImage imageWithContentsOfFile:fileName];
[image drawInRect:self.bounds];

Answer 1

As of when this question was first asked, creating an IB-designable control required packaging it in a framework target. You don't have to do that anymore — the shipping Xcode 6.0 (and later) will preview IB-designable controls from your app target, too. However, the problem and the solution are the same.

Why? [NSBundle mainBundle] returns the primary bundle of the currently running app. When you call that from a framework, you're getting a different bundle returned based on which app is loading your framework. When you run your app, your app loads the framework. When you use the control in IB, a special Xcode helper app loads the framework. Even if your IB-designable control is in your app target, Xcode is creating a special helper app to run the control inside of IB.

The solution? Call +[NSBundle bundleForClass:] instead (or NSBundle(forClass:) in Swift). This gets you the bundle containing the executable code for whichever class you specify. (You can use [self class]/self.dynamicType there, but beware the result will change for subclasses defined in different bundles.)

If you're using the framework approach — which can be useful for some apps even though it's no longer required for IB-designable controls — it's best to put image resources in the same framework with the code that uses them. If your framework code expects to use resources provided at run time by whatever app loads the framework, the best thing to do for making it IB-designable is to fake it. Implement the prepareForInterfaceBuilder method in your control and have it load resources from a known place (like the framework bundle or a static path in your Xcode workspace).