title: Xamarin.Android attributes showing "not declared"
body: <p>I am new to Xamarin and especially xml, but I have run into a problem that I have not been able to resolve with any solution after hours of searching. I am trying to use the "android.support.percent" package to use percent margins on a relative layout. I have installed the proper NuGet packages to support it too. It worked for a little while, but now it has suddenly started giving me multiple warnings and messages throughout the file.   </p>
  
  <p>The first error is simply "The 'PercentRelativeLayout' attribute is not declared." This is just the name given to my starting xml tag. Here is the code:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;PercentRelativeLayout 
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:id="@+id/percentRelativeLayout"
      android:background="#000000"&gt;
  </code></pre>
  
  <p>Second, four warnings appear in the AndroidManifest with a similar message: "The '<a href="http://schemas.android.com/apk/res/android:xxxx" rel="nofollow noreferrer">http://schemas.android.com/apk/res/android:xxxx</a>' attribute is not declared." where 'xxxx' is versionCode, versionName, label, and icon. The manifest file is not very extensive at all: </p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;manifest xmlns:android="http://schemas.android.com/apk/res/android" 
      package="MyProject.MyProject" android:versionCode="1" 
      android:versionName="1.0"&gt;
      &lt;uses-sdk /&gt;
      &lt;application android:label="MyProject" 
      android:icon="@drawable/Icon"&gt;&lt;/application&gt;
  &lt;/manifest&gt;
  </code></pre>
  
  <p>On top of all this, there are 4 messages showing that say:<br>
  "Could not find schema information for the element 'manifest'."<br>
  "Could not find schema information for the attribute 'package'."<br>
  "Could not find schema information for the attribute 'uses-sdk'."<br>
  "Could not find schema information for the element 'application'."  </p>
  
  <p>What does all this mean and how can I get back to actually developing this app?</p>