解决方法
不幸的是,NSURL不会告诉您URL创建失败的原因.
在NSURL上执行ALT CLICK时从Xcode弹出窗口中：
Handling Object Creation Failure
The NSURL class fails to create a new NSURL object if the path being passed is not well formed; the path must comply with RFC 2396. Examples of cases that will not succeed are strings containing space characters and high-bit characters. If creating an NSURL object fails,the creation methods return nil,which you must be prepared to handle.
因此如果失败,NSURL将返回nil,而不提供任何进一步的细节.通常使用可选绑定,可选链接,防护或任何其他已知技术来安全地解包选项,并遵循Fogmeister的建议并在使用前对URL字符串进行编码.
