各种第一次遇到的android studio报错

• All packages are not available for download!  The following packages are not available:

- Package id build-tools;27.0.3

解决方法：File->settings->Appearance & Behavior->System Settings->HTTP Proxy->勾选No proxy ​​​​​​​​​​​​​​

• Unable to resolve dependency for ‘:app@debug/compileClasspath’: Could not resolve com.android.support:appcompat-v7:27.1.1.

解决方法：

设置里面关代理然后在gradle.properties里注释代码

• Failed to load AppCompat ActionBar with unknown error.

在style.xml文件中找到下面这行代码，前面加上“Base.”