描述你的问题 Pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) 警告如上程序运行正常,全部加上__nonnull 就好了,为什么? 贴上相关代码 {代码...} .h文件 贴上...
1、java官方教程里有一段话,解释了原因:One reason why the Java programming language does not permit you to extend more than one class is to avoid the issues of multiple inheritance of state, which ...