Objective-C Category Causing unrecognized selector

问题:

My project has a UIImage category function that I want to call from another class. I properly import the header file for the image category and I get the project to compile with no warning.

The problem is that when I call the UIImage category function I seen an unrecognized selector error with a NSInvalidArgumentException. Why am I seeing this if I've properly linked everything?

#import <UIKit/UIKit.h>

@interface UIImage (DRShare)

+ (UIImage*) imageNamed:(NSString*)name;

@end


@implementation UIImage (DRShare)

+ (UIImage*) imageNamedDR:(NSString*)name{

    CGFloat s = 1.0f;
    if([[UIScreen mainScreen] respondsToSelector:@selector(scale)]){
        s = [[UIScreen mainScreen] scale];
    }

    NSString *path = [NSString stringWithFormat:@"%@%@%@.png",kImagesPath,name,s > 1 ? @"@2x":@""];
    return [UIImage imageWithContentsOfFile:DRBUNDLE(path)];
}

@end

file that calls it:

        backgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamedDR:@"Share Popup Background"]];

exception raised:

2010-10-22 11:51:02.880 Stuff[11432:207] +[UIImage imageNamedDR:]: unrecognized selector sent to class 0x1f8e938
2010-10-22 11:51:02.883 Stuff[11432:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+[UIImage imageNamedDR:]: unrecognized selector sent to class 0x1f8e938'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x02e65b99 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x02fb540e objc_exception_throw + 47
    2   CoreFoundation                      0x02e6776b +[NSObject(NSObject) doesNotRecognizeSelector:] + 187
    3   CoreFoundation                      0x02dd72b6 ___forwarding___ + 966
    4   CoreFoundation                      0x02dd6e72 _CF_forwarding_prep_0 + 50
    5   TapTapShare                         0x0001291c -[DRShareViewController backgroundView] + 127
    6   TapTapShare                         0x00012343 -[DRShareViewController loadView] + 639
    7   UIKit                               0x0044f54f -[UIViewController view] + 56
    8   UIKit                               0x0044d9f4 -[UIViewController contentScrollView] + 42
    9   UIKit                               0x0045d7e2 -[UINavigationController _computeAndApplyScrollContentInsetDeltaForViewController:] + 48
    10  UIKit                               0x0045bea3 -[UINavigationController _layoutViewController:] + 43
    11  UIKit                               0x0045d12d -[UINavigationController _startTransition:fromViewController:toViewController:] + 524
    12  UIKit                               0x00457ccd -[UINavigationController _startDeferredTransitionIfNeeded] + 266
    13  UIKit                               0x00574b55 -[UILayoutContainerView layoutSubviews] + 226
    14  QuartzCore                          0x02616481 -[CALayer layoutSublayers] + 177
    15  QuartzCore                          0x026161b1 CALayerLayoutIfNeeded + 220
    16  QuartzCore                          0x026160bd -[CALayer layoutIfNeeded] + 111

回答1:

A couple possibilities:

1. You did not link UIImage+TTShare.m into your target. So while you have the header, you're not compiling the implementation.
2. If this is part of a static library, you need to add -all_load to the Other Linker Flags build setting for the app linking against the library.

回答2:

If you want to use Category method, you must add -ObjC to the Other Linker Flags build setting of your APP.

回答3:

I had the same issue and had to apply this fix as well. My NSDate-Extensions.m source file wasn't compiling so I had to go into Project Settings, then select the appropriate target, then click the "Build Phases" tab, then expand the "Compile Sources" items, then click the + symbol and manually add my NSDate-Extensions.m file.

回答4:

I had this error message and I am using Cocoapods. To fix the error, I just needed to call pod install again to create all the necessary linking correctly.

回答5:

Another possibility.

You have the implementation of category but do not have an interface. I mean you forgot to declare in *.h the interface of your category.

回答6:

Yet another possibility:

This is almost too embarrassing to admit, but just in case someone might have done the same silly mistake:

I was copying code from one project to another, and by mistake I had pasted the same source code in the .h file and the .m file (in both I had put the code meant for the .h file). I fixed my .m file and it worked.

回答7:

May be because you write imageNamed instead of imageNamedDR in the interface..