objective-c - 由于“nil”类的未捕获异常，什么情况会导致应用程序终止

Question

我的应用程序偶尔崩溃

2012-10-10 23:19:24.039 [26442:850f] -[NSNull allKeys]: unrecognized selector sent to instance 0x7fff741cbea0
2012-10-10 23:19:24.040 [26442:850f] *** Terminating app due to uncaught exception of class 'nil'

[obj isKindOfClass:[NSDictionary class]]该对象在调用之前已经过测试allKeys:

如果我[[NSNull null] allKeys]故意打电话，它会崩溃

2012-10-11 16:22:15.606 [14939:403] -[NSNull allKeys]: unrecognized selector sent to instance 0x7fff73659f00
2012-10-11 16:22:15.622 [14939:403] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull allKeys]: unrecognized selector sent to instance 0x7fff73659f00'

我想知道是什么情况导致的Terminating app due to uncaught exception of class 'nil'，所以我可以调试这个问题。

Answer 1

1：因为NSNull没有响应消息[allKeys]，所以抛出异常。

2：您应该检查您的对象是否可以 [respondsToSelector:@selector(allKeys)]

3：如果你的NSNull类对象通过了[obj isKindOfClass:[NSDictionary class]]，那么你的控制语句有问题