[android] Failed to resolve: com.android.support:appcompat-v7:28.0

some guys who still might have the problem like me (FOR IRANIAN and all the coutries who have sanctions) , this is error can be fixed with proxy i used this free proxy for android studio 3.2 https://github.com/freedomofdevelopers/fod just to to Settings (Ctrl + Alt + S) and search HTTP proxy then check Manual proxy configuration then add fodev.org for host name and 8118 for Port number

Screenshot of proxy settings in android studio