1. 第一种区分平台,在cs文件中区分, Device.OnPlatform 推荐

public UiRightViewModel()
{

    Device.OnPlatform(
        iOS: () =>
        {
            this.ThrottleViewWidth = 190 * AppSetting.Instance.HeightScale;
            this.ThrottleViewHeight = 200 * AppSetting.Instance.WidthScale;
        },
        Android: () => {
            this.ThrottleViewWidth = 190 * 3 * AppSetting.Instance.HeightScale;
            this.ThrottleViewHeight = 69 * 3 * AppSetting.Instance.WidthScale;
        }
    );
}

2. 第二种区分平台 ,xaml文件中, ContentPage.Resources

<? xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns = "http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Name="Page"
             xmlns:local="clr-namespace:XamlSamples;assembly=XamlSamples"
             x:Class="XamlSamples.ListViewDemoPage"
             Title="ListView Demo Page">

  <ContentPage.Resources>
    <ResourceDictionary>
      <OnPlatform x:Key="boxSize"
                  x:TypeArguments="x:Double"
                  iOS="50"
                  Android="50"
                  WinPhone="75" />ContentView

      <!-- This is only an issue on the iPhone; Android and
           WinPhone auto size the row height to the contents. -->
      <OnPlatform x:Key="rowHeight" 
                  x:TypeArguments="x:Int32"
                  iOS ="100"    
                  Android="{Binding Path=Width,Source={x:Reference Page}}"
                  WinPhone="85" />

      <local:DoubleToIntConverter x:Key="intConverter" />
      
    </ResourceDictionary>
  </ContentPage.Resources>

  <ListView ItemsSource = "{x:Static local:NamedColor.All}"
            RowHeight="{StaticResource rowHeight}">
    <ListView.ItemTemplate>
      <DataTemplate>
        <ViewCell>
          <ViewCell.View>
            <StackLayout Padding = "5, 5, 0, 5"
                         Orientation="Horizontal"
                         Spacing="15">
              
              <BoxView WidthRequest = "{StaticResource boxSize}"
                       HeightRequest="{StaticResource boxSize}"
                       Color="{Binding Color}" />
              
              <StackLayout Padding = "5, 0, 0, 0"
                           VerticalOptions="Center" BackgroundColor = "Green" >
                
                <Label Text = "{Binding FriendlyName}"
                       Font="Bold, Medium" BackgroundColor = "Red" />

                <StackLayout Orientation = "Horizontal"
                             Spacing="0" BackgroundColor = "Purple">
                  <Label Text = "{Binding Color.R,
                                   Converter={StaticResource intConverter},
                                   ConverterParameter=255,
                                   StringFormat='R={0:X2}'}" BackgroundColor = "Yellow" />
                  <Label Text = "{Binding Color.G,
                                   Converter={StaticResource intConverter},
                                   ConverterParameter=255,
                                   StringFormat=', G={0:X2}'}" BackgroundColor = "Red" />
                  <Label Text = "{Binding Color.B,
                                   Converter={StaticResource intConverter},
                                   ConverterParameter=255,
                                   StringFormat=', B={0:X2}'}" BackgroundColor = "Gray" />
                </StackLayout>
              </StackLayout>
            </StackLayout>
          </ViewCell.View>
        </ViewCell>
      </DataTemplate>
    </ListView.ItemTemplate>
  </ListView>
</ContentPage>  

3. 第三种区分平台,xaml文件中

          <Slider   HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" ValueChanged="Slider_OnValueChanged"
                            Minimum="0" Maximum="100" Rotation="0" Value="50" BackgroundColor = "Transparent" Opacity = "1">
            <Slider.Effects>
              <effects:SliderEffect ThumbImage="button_flightpage_unlock.png"
                                TrackImage="transparent_image.png"
                                ReturnPosition="Start"
                                SlideToEnd="SliderEffect_OnSlideToEnd"
                                TrackInset = "30"   >
                                <effects:SliderEffect.ThumbImageHeight>
                                    <OnPlatform x:TypeArguments="x:Double">
                                        <OnPlatform.Android>120</OnPlatform.Android>
                                        <OnPlatform.iOS>60</OnPlatform.iOS>
                                    </OnPlatform>
                                </effects:SliderEffect.ThumbImageHeight>
                                
                                <effects:SliderEffect.ThumbImageWidth>
                                    <OnPlatform x:TypeArguments="x:Double">
                                        <OnPlatform.Android>120</OnPlatform.Android>
                                        <OnPlatform.iOS>60</OnPlatform.iOS>
                                    </OnPlatform>
                                </effects:SliderEffect.ThumbImageWidth>
                    </effects:SliderEffect>
            </Slider.Effects>
          </Slider>

核心代码

<effects:SliderEffect.ThumbImageWidth>
                                    <OnPlatform x:TypeArguments="x:Double">
                                        <OnPlatform.Android>120</OnPlatform.Android>
                                        <OnPlatform.iOS>60</OnPlatform.iOS>
                                    </OnPlatform>
                                </effects:SliderEffect.ThumbImageWidth>

4. 第四种使用方式,简便写法

this.Padding = new Thickness (10, Device.OnPlatform (20, 0, 0), 10, 5);