一、 更新sdk，遇到了更新下载失败问题：
Fetching https://dl-ssl.google.com/android/repository/addons_list-2.xml
Fetched Add-ons List successfully
Fetching URL: https://dl-ssl.google.com/android/repository/repository-8.xml
Done loading packages.
Fetching https://dl-ssl.google.com/android/repository/addons_list-2.xml
Failed to fetch
URL https://dl-ssl.google.com/android/repository/addons_list-2.xml, reason: Connection to https://dl-ssl.google.com refused Fetched Add-ons List successfully Fetching URL: https://dl-ssl.google.com/android/repository/repository-8.xml
Failed to fetch URL https://dl-ssl.google.com/android/repository/repository-8.xml, reason: HttpHostConnect Connection to https://dl-ssl.google.com refused Done loading packages.
解决方案如下：
解决国内访问Google服务器的困难：
1）.启动 Android SDK Manager ；
2）.打开主界面，依次选择「Tools」、「Options...」，弹出『Android SDK Manager - Settings』窗口；
3）.在『Android SDK Manager - Settings』窗口中，在「HTTP Proxy Server」和「HTTP Proxy Port」输入框内填入mirrors.neusoft.edu.cn和80，并且选中「Force https://... sources to be fetched using http://...」复选框；
4）.设置完成后单击「Close」按钮关闭『Android SDK Manager - Settings』窗口返回到主界面；
5）.重启 Manager