objc_msgSend发送alloc和init产生的问题

Question

问题 用objc_msgSend分开发送alloc init则正确运行，一起发送就crash了，请问下是为什么，而且只是在添加到self.view的时候才crash？

//最后一行出错
UIView *view = ((UIView *(*)(id,SEL,SEL))objc_msgSend)([UIView class],@selector(alloc),@selector(init));
((void (*)(id,SEL,CGRect))objc_msgSend)(view,@selector(setFrame:),self.view.bounds);
((void (*)(id,SEL,UIColor *))objc_msgSend)(view,@selector(setBackgroundColor:),[UIColor orangeColor]);
((void (*)(id,SEL,id))objc_msgSend)(self.view,@selector(addSubview:),view);//Thread 1:EXC_BAD_ACCESS(code=1,adress=0x0)

//正确运行
UIView *view = ((UIView *(*)(id,SEL))objc_msgSend)([UIView class],@selector(alloc));
view = ((UIView *(*)(id,SEL))objc_msgSend)(view,@selector(init));
((void (*)(id,SEL,CGRect))objc_msgSend)(view,@selector(setFrame:),self.view.bounds);
((void (*)(id,SEL,UIColor *))objc_msgSend)(view,@selector(setBackgroundColor:),[UIColor orangeColor]);
((void (*)(id,SEL,id))objc_msgSend)(self.view,@selector(addSubview:),view);

Answer 1

你第一行并没有 init，只是把 @selector(init) 做为 alloc 方法的参数了，等价于：

UIView *view = [UIView alloc:@selector(init)];

然而 alloc 方法是没有参数的，在运行时忽略了