按照书上的操作一步步输入，当用Cycript注入Mail时，输入?expand没有返回值，查看视图结构时，返回null
iPhone:~ root# cycript -p MobileMail
cy# ?expand
cy# [[UIApp keyWindow] recursiveDescription]
null
cy# [[[UIApplication sharedApplication] keyWindow] recursiveDescription]
null
看之前又说加.toString(),加上后打印如下
cy# [[UIApp keyWindow] recursiveDescription].toString()
throw new TypeError(‘null is not an object (evaluating ‘objc_msgSend(objc_msgSend(UIApp,“keyWindow”),“recursiveDescription”).toString’)’)
请问怎么解决