title: Unknown type 'ContentPage' in XML namespace 'http://xamarin.com/schemas/2014/forms'
body: <p>I'm writing an application in MVVM.
  My MainPage.xaml looks like this:</p>
  
  <pre><code>    &lt;?xml version="1.0" encoding="utf-8" ?&gt;
      &lt;ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                   xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                   xmlns:view="using:FIARView"
                   xmlns:controls="using:DLToolkit.Forms.Controls;assembly=DLToolkit.Forms.Controls.FlowListView"
                   x:Class="clr-namespace:FIARView.MainPage"&gt;
  ...
  </code></pre>
  
  <p>And everything that I use in this xaml file has an error:
  for example:</p>
  
  <pre><code>Unknown type 'ContentPage' in XML namespace 'http://xamarin.com/schemas/2014/forms'
  Unknown type 'Button' in XML namespace 'http://xamarin.com/schemas/2014/forms'
  </code></pre>
  
  <p>etc.
  I tried searching for an answer but didn't find it. How can I solve this problem?</p>