Demo de utilização da Câmera - Xamarin.Forms http://julianocustodio.com/camera-xamarin-forms

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionCode="1" android:versionName="1.0" package="com.companyname.DemoCamera" android:installLocation="auto">
	<uses-sdk android:minSdkVersion="15" />
	<uses-permission android:name="android.permission.CAMERA" />
	<application android:label="DemoCamera.Android">
	  	<provider android:name="android.support.v4.content.FileProvider"
	            android:authorities="com.companyname.DemoCamera.fileprovider"
	            android:exported="false"
	            android:grantUriPermissions="true">

	    	<meta-data android:name="android.support.FILE_PROVIDER_PATHS"
	               android:resource="@xml/file_paths"></meta-data>
	  	</provider>
  	</application>
</manifest>