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.
Mono Framework
Download the Mono Framework v4.8.0 archive to any directory on your disk, double-click it and follow the instructions on screen. Please accept all the defaults during the installation, including the target drive.

Java SDK
Mac OS X uses its own version of Java and in order to install it you need to start the terminal app and type the following command:
javac -version
After typing it you should see a Mac OS X system popup which will guide you to install the Java software.
Android SDK
Download the Android SDK for Mac OS X version 24.4.1, open the downloaded archive and copy the contents of the folder found at its root directory (most probably named android-sdk-macosx) to the /Users/jhli/Library/Developer/Xamarin/android-sdk-macosx directory.

Click here in order to start the Android SDK Manager application. In the GUI make sure the following components are installed or selected for installation:

Android SDK Tools
Android SDK Platform-tools
Android SDK Build-tools
Android API 15
Android API 19
Android API 21
Once all the required components are selected (you can select others as well, if you wish) start the installation.
If you cannot see /Users/jhli/Library/Developer/Xamarin/android-sdk-macosx in Finder please click here to reveal the directory in Finder.

Download the Android NDK for Mac OS X version r10e, open the downloaded archive and copy the contents of its root directory (most probably named android-ndk-r10e) to the /Users/jhli/Library/Developer/Xamarin/android-ndk directory.

When the Android SDK installation is finished you might want to start the Android Emulator Manager and create as many emulator images as you might need for your development. This step can be performed at any time, on an as-needed basis.

Visual Studio for Mac Preview
Download the Visual Studio for Mac Preview v7.0.0 archive to any directory on your disk, double-click it and then drag and drop the Visual Studio for Mac Preview icon to the Applications folder.

Xamarin.Android
Download the Xamarin.Android v7.1.0 archive to any directory on your disk, double-click it and follow the instructions on screen. Please accept all the defaults during the installation, including the target drive.

Xamarin.iOS
Download the Xamarin.iOS v10.4.0 archive to any directory on your disk, double-click it and follow the instructions on screen. Please accept all the defaults during the installation, including the target drive.

Xamarin.Mac
Download the Xamarin.Mac v3.0.0 archive to any directory on your disk, double-click it and follow the instructions on screen. Please accept all the defaults during the installation, including the target drive.