How can I show text with html format in xamarin forms

This should work for you

string htmlText = MyItem.Article.ToString().Replace(@"\", string.Empty);
var browser = new WebView ();
var html = new HtmlWebViewSource {
  Html = htmlText
};
browser.Source = html;

Because Xamarin.Forms.HtmlWebViewSource.HTML expect a pure HTML. Using this you can create a Xamarin.Forms user control with the help of this article http://blog.falafel.com/creating-reusable-xaml-user-controls-xamarin-forms/ Cheers..!

In XAML you can do something like this:

<WebView>
   <WebView.Source>
      <HtmlWebViewSource Html="{Binding HtmlText}"/>
   </WebView.Source>
</WebView>

You may also need to provide Height and Width of the WebView if it's not inside a Grid.