缺少ios开发签名身份(null)

当我尝试生成ipa文件时,我收到此错误.无法解决.请帮我解决此错误：

我有自己的帐户,在我的钥匙链中访问它的鞋子像这样：

我没有使用新的Mac,我已经创建了ipa .Day.但今天无法做到.我也有.cer个人资料.它有效

解决方法

这是Apple发表的声明.

Thanks for bringing this to the attention of the community and apologies for the issues you’ve been having. This issue stems from having a copy of the expired WWDR Intermediate certificate in both your System and Login keychains. To resolve the issue,you should first download and install the new WWDR intermediate certificate (by double-clicking on the file). Next,in the Keychain Access application,select the System keychain. Make sure to select “Show Expired Certificates” in the View menu and then delete the expired version of the Apple Worldwide Developer Relations Certificate Authority Intermediate certificate (expired on February 14,2016). Your certificates should Now appear as valid in Keychain Access and be available to Xcode for submissions to the App Store.

https://forums.developer.apple.com/thread/37208

>下载https://developer.apple.com/certificationauthority/AppleWWDRCA.cer
并双击以安装到Keychain.
>选择“查看” – > Keychain app中的“显示过期的证书”.
>从Keychain应用程序的“登录”选项卡和“系统”选项卡中删除Apple Worldwide Developer Relations Certificate Authority证书.

确保新下载的证书同时包含登录和系统默认只有系统选项卡仍然会出错.**