didFailLoadWithError():

Error Domain=NSURLErrorDomain Code=-1022 "The resource could not be loaded because the App Transport Security policy requires the use of a secure connection." UserInfo={NSUnderlyingError=0x7fce0c9ac400 {Error Domain=kCFErrorDomainCFNetwork Code=-1022 "The resource could not be loaded because the App Transport Security policy requires the use of a secure connection." UserInfo={NSErrorFailingURLStringKey=http://www.baidu.com/, NSLocalizedDescription=The resource could not be loaded because the App Transport Security policy requires the use of a secure connection., NSErrorFailingURLKey=http://www.baidu.com/}}, NSErrorFailingURLStringKey=http://www.baidu.com/, NSErrorFailingURLKey=http://www.baidu.com/, NSLocalizedDescription=The resource could not be loaded because the App Transport Security policy requires the use of a secure connection.}

Google后查证，iOS9引入了新特性App Transport Security (ATS)。详情：App Transport Security (ATS)

新特性要求App内访问的网络必须使用HTTPS协议。
但是现在公司的项目使用的是HTTP协议，使用私有加密方式保证数据安全。现在也不能马上改成HTTPS协议传输。

最终找到以下解决办法：

1. 在Info.plist中添加NSAppTransportSecurity类型Dictionary。
2. 在NSAppTransportSecurity下添加NSAllowsArbitraryLoads类型Boolean,值设为YES