Is it possible to mix OnIdiom and OnPlatform in XAML (Xamarin.Forms)?

Question

For UWP I need a different size for the width of a column in a Grid. Additionally, the value should be different on tablet and on smartphone.

The following code crashes the app

<ColumnDefinition>
    <ColumnDefinition.Width>
        <OnIdiom.Phone>
            <OnPlatform x:TypeArguments="GridLength" iOS="*" Android="*" WinPhone="100" />
        </OnIdiom.Phone>
        <OnIdiom.Tablet>
            <OnPlatform x:TypeArguments="GridLength" iOS="*" Android="*" WinPhone="200" />
        </OnIdiom.Tablet>
    </ColumnDefinition.Width>
</ColumnDefinition>

with

Type OnIdiom.Phone not found in xmlns http://xamarin.com/schemas/2014/forms

The code is in a ViewCell. So I can't use an additional ResourceDictionary and also OnSizeAllocated() is not available in the code behind file.

Is it possible to use OnIdiom and OnPlatform together?

Answer 1

OnIdiom, just like OnPlatform is an object you have to declare. In your case, you're setting OnIdiom.Phone property to an object that doesn't have those.

Your Xaml should look more like:

<ColumnDefinition>
  <ColumnDefinition.Width>
    <OnIdiom x:TypeArguments="GridLength">
      <OnIdiom.Phone>
        <OnPlatform x:TypeArguments="GridLength" iOS="*" Android="*" WinPhone="100" />
      </OnIdiom.Phone>
      <OnIdiom.Tablet>
        <OnPlatform x:TypeArguments="GridLength" iOS="*" Android="*" WinPhone="200" />
      </OnIdiom.Tablet>
    </OnIdiom>
  </ColumnDefinition.Width>
</ColumnDefinition>