Info.plist文件添加key

App Transport Security Settings

Allow Arbitrary Loads  —>>>bool yes.

在编写SDWebImage Demo时，遇到某些gif加载失败，提示以下错误：

App Transport Security has blocked a cleartext HTTP (http://) resource load since it is insecure. Temporary exceptions can be configured via your app’s Info.plist file.

Cannot start load of Task .<3> since it does not conform to ATS policy

iOS9中新增App Transport Security（简称ATS）特性, 主要将原来请求的时候用到的HTTP，都转向TLS1.2协议进行传输。这也意味着所有的HTTP协议都强制使用了HTTPS协议进行传输。原文如下：

App Transport Security (ATS) enforces best practices in the secure connections between an app and its back end. ATS prevents accidental disclosure, provides secure default behavior, and is easy to adopt; it is also on by default in iOS 9 and OS X v10.11. You should adopt ATS as soon as possible, regardless of whether you’re creating a new app or updating an existing one. 

If you’re developing a new app, you should use HTTPS exclusively. If you have an existing app, you should use HTTPS as much as you can right now, and create a plan for migrating the rest of your app as soon as possible. In addition, your communication through higher-level APIs needs to be encrypted using TLS version 1.2 with forward secrecy. If you try to make a connection that doesn’t follow this requirement, an error is thrown. If your app needs to make a request to an insecure domain, you have to specify this domain in your app’s Info.plist file.

ATS是在iOS 9.0 和 OS X v10.11版本中增加的特性，使用iOS 9.0或者OS X v10.11的SDK版本（或更新的SDK）进行编译应用时会默认启动ATS。则需要对ATS进行配置。如果使用iOS 9.0或者OS X v10.11之前的SDK版本编译的应用默认是禁止ATS的，因此不会影响应用的网络连接方面的功能（即使在iOS 9.0的机子上跑也是不影响的）。

其实ATS并不单单针对HTTP进行了限制，对HTTPS也有一定的要求，以百度的地址为例（注：举该栗子的时候百度是还没符合ATS的要求的，现在百度已经支持ATS），如果在App中请求https://www.baidu.com的话，是会收到如下的错误信息：

NSURLSession/NSURLConnection HTTP load failed (kCFStreamErrorDomainSSL, -9802)