为"无法识别的选择器"异常设置默认处理程序

Question

在Objective-C中,有没有办法设置默认的处理程序以避免unrecognizedselector异常？我想做NSNULL和NSNumber响应所有的方法NSString.

谢谢!

Answer 1

为了处理“无法识别的选择器”异常，我们应该重写两个方法：

- (void)forwardInvocation:(NSInvocation *)anInvocation;
- (NSMethodSignature*)methodSignatureForSelector:(SEL)selector;

在这种情况下，如果我们希望 NSNull 在发生“无法识别的选择器”异常时执行 NSSString 方法，我们应该这样做：

@interface NSNull (InternalNullExtention)
@end



@implementation NSNull (InternalNullExtention)

- (NSMethodSignature*)methodSignatureForSelector:(SEL)selector
{
    NSMethodSignature* signature = [super methodSignatureForSelector:selector];
    if (!signature) {
        signature = [@"" methodSignatureForSelector:selector];
    }
    return signature;
}

- (void)forwardInvocation:(NSInvocation *)anInvocation
{
    SEL aSelector = [anInvocation selector];

    if ([@"" respondsToSelector:aSelector])
        [anInvocation invokeWithTarget:@""];
    else
        [self doesNotRecognizeSelector:aSelector];
}
@end