when installing xamarin , it stops after a while and it says " error downloading from google server.Android SDK" I tried installation several times , but failed. It sometimes says : It was not possible to complete an automatic installation. This might be due to a problem with your network, proxy servers or an unsolvable installation conflict. At this point, you can continue the installation by manually downloading and installing the independent pieces. The list below shows each component that you need to install.
What can I do to complete the xamarin installation to the End ???
Download the Android SDK manually and install it yourself, then retry installing the Xamarin tools.
You can find the latest SDK version on the bottom of this page https://developer.android.com/studio/index.html
The Xamarin installer should detect on its own that the Android SDK is already installed.