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>

Answer 2

Much nicer syntax as of Xamarin.Forms v3.2 (via new built-in XAML extensions):

<Grid.ColumnDefinitions>
    <ColumnDefinition Width="{OnIdiom 
        Phone= {OnPlatform iOS=*, Android=*, UWP=100 },
        Tablet= {OnPlatform iOS=*, Android=*, UWP=200 }}">
    </ColumnDefinition>
</Grid.ColumnDefinitions>

Answer 3

Xamarin.Forms Xaml Example:

<OnPlatform x:TypeArguments="View">
    <OnPlatform.Android>
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition>
                    <ColumnDefinition.Width>
                        <OnIdiom x:TypeArguments="GridLength" Tablet="100" Phone="50" />
                    </ColumnDefinition.Width>
                </ColumnDefinition>
                <ColumnDefinition>
                    <ColumnDefinition.Width>
                        <OnIdiom x:TypeArguments="GridLength" Tablet="100" Phone="50" />
                    </ColumnDefinition.Width>
                </ColumnDefinition>
            </Grid.ColumnDefinitions>
        </Grid>
    </OnPlatform.Android>
    <OnPlatform.iOS>
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition>
                    <ColumnDefinition.Width>
                        <OnIdiom x:TypeArguments="GridLength" Tablet="100" Phone="50" />
                    </ColumnDefinition.Width>
                </ColumnDefinition>
                <ColumnDefinition>
                    <ColumnDefinition.Width>
                        <OnIdiom x:TypeArguments="GridLength" Tablet="100" Phone="50" />
                    </ColumnDefinition.Width>
                </ColumnDefinition>
            </Grid.ColumnDefinitions>
        </Grid>
    </OnPlatform.iOS>
</OnPlatform>

Answer 4

Here is the solution to mix OnIdiom and OnPlatform in xaml. For Example, there are variations in stack layout padding then we can do this as follows -

   <StackLayout.Padding>
                        <OnIdiom x:TypeArguments="Thickness">
                        <OnIdiom.Phone>
                            <OnPlatform x:TypeArguments="Thickness" iOS="0,40,0,0" Android="15,0" WinPhone="15,0" />
                        </OnIdiom.Phone>
                        <OnIdiom.Tablet>
                            <OnPlatform x:TypeArguments="Thickness" iOS="15,0" Android="15,0" WinPhone="15,0" />
                        </OnIdiom.Tablet>
                      </OnIdiom>

</StackLayout.Padding>

Answer 5

One option which works in code is to use

if(Device.OS == TargetPlatform.Windows && Device.Idiom == TargetIdiom.Phone)
    this.innerGrid.ColumnDefinitions.First().Width = new GridLength(100);

to overwrite the existing Xaml definition. innerGrid is the name of the Grid used in the Xaml.