The Device class contains a number of properties and methods to help developers customize layout and functionality on a per-platform basis.

In addition to methods and properties to target code at specific hardware types and sizes, the Device class includes the BeginInvokeOnMainThread method which should be used when interacting with UI controls from background threads.

Device.Idiom

The Device.Idiom can be used to alter layouts or functionality depending on whether the device is a phone or a tablet. The TargetIdiom enumeration contains four values:

• Phone – iPhone, iPod touch, Windows Phone, Android devices narrower than 600 dips^
• Tablet – iPad, Windows 8.1 computers, Android devices wider than 600 dips^
• Desktop – only returned in UWP apps (currently in Preview) on Windows 10
• Unsupported – unused

^ dips is not necessarily the physical pixel count

Idiom is especially useful for building layouts that take advantage of larger screens, like this:

if (Device.Idiom == TargetIdiom.Phone) {
    // layout views vertically
} else {
    // layout views horizontally for a larger display (tablet or desktop)
}

Device.OS

Device.OS will be set to one of the values of the TargetPlatform enumeration:

• iOS
• Android
• WinPhone (returned for Windows 8 Silverlight)
• Windows (returned for Windows 8.1, Windows Phone 8.1, and all UWP/Windows 10 devices)

This enables platform-specific checks to alter layout or functionality, such as these if statements:

if (Device.OS == TargetPlatform.iOS) {
    // move layout under the status bar
    stackLayout.Padding = new Thickness (0, 20, 0, 0);
}

Font font;

if (Device.OS == TargetPlatform.iOS) {
  font = Font.OfSize ("MarkerFelt-Thin", Device.GetNamedSize (NamedSize.Medium, typeof(Label)));
} else {
  font = Font.SystemFontOfSize (Device.GetNamedSize (NamedSize.Medium, typeof(Label)));
}

label.FontFamily = font.FontFamily;
label.FontAttributes = font.FontAttributes;
label.FontSize = font.FontSize;

Device.OnPlatform

Device.OnPlatform is a generic method that has three optional parameters: iOS, Android, and WinPhone. It can be used to provide platform-specific values

// left and right padding: 5; top padding: 20 (only on iOS)
layout.Padding = new Thickness (5, Device.OnPlatform(20,0,0), 5, 0),

It also accepts Action parameters to execute multiple platform-specific instructions. This overload accepts an additional Default parameter.

Device.OnPlatform(
    Android: () =>{
         PositiveBalance = PositiveBalance.AddLuminosity(0.3);
         NegativeBalance = NegativeBalance.AddLuminosity(0.3);
         SubTitle = Color.FromRgb(115, 129, 130);
        },
    WinPhone: () =>{
          PositiveBalance = PositiveBalance.AddLuminosity(0.3);
          NegativeBalance = NegativeBalance.AddLuminosity(0.3);
        }
    );

Using Xaml

OnPlatform can also be used in Xaml as shown on the BoxView control below which sets two different attributes using . There is a built-in type converter for Color so we can set that attribute using BoxView.Color element syntax. The WidthRequest property is a double so that is set using x:TypeArguments="x:Double":

<BoxView HorizontalOptions="Center">
  <BoxView.Color>
    <OnPlatform x:TypeArguments="Color"
      iOS="Green"
      Android="#738182"
      WinPhone="Accent" />
  </BoxView.Color>
  <BoxView.WidthRequest>
    <OnPlatform x:TypeArguments="x:Double"
      iOS="30"
      Android="40"
      WinPhone="50" />
  </BoxView.WidthRequest>
</BoxView>

Device.Styles

The Styles property contains built-in style definitions that can be applied to some controls' (such as Label) Style property. The available styles are:

• BodyStyle
• CaptionStyle
• ListItemDetailTextStyle
• ListItemTextStyle
• SubtitleStyle
• TitleStyle

Device.GetNamedSize

GetNamedSize can be used when setting FontSize in C# code:

myLabel.FontSize = Device.GetNamedSize (NamedSize.Small, myLabel);
someLabel.FontSize = Device.OnPlatform (
      24,         // hardcoded size
      Device.GetNamedSize (NamedSize.Medium, someLabel),
      Device.GetNamedSize (NamedSize.Large, someLabel)
);

Device.OpenUri

The OpenUri method can be used to trigger operations on the underlying platform, such as open a URL in the native web browser (Safari on iOS or Internet on Android).

Device.OpenUri(new Uri("https://evolve.xamarin.com/"));

The WebView sample includes an example using OpenUri to open URLs and also trigger phone calls.

The Maps sample also uses Device.OpenUri to display maps and directions using the native Maps apps on iOS and Android.

Device.StartTimer

The Device class also has a StartTimer method which provides a simple way to trigger time-dependent tasks that works in Xamarin.Forms common code (including PCLs). Pass a TimeSpan to set the interval and return true to keep the timer running or false to stop it after the current invocation.

Device.StartTimer (new TimeSpan (0, 0, 60), () => {
    // do something every 60 seconds
    return true; // runs again, or false to stop
});

If the code inside the timer interacts with the user-interface (such as setting the text of a Label or displaying an alert) it should be done inside a BeginInvokeOnMainThread expression (see below).

Device.BeginInvokeOnMainThread

User interface elements should never be accessed by background threads, such as code running in a timer or a completion handler for asynchronous operations like web requests. Any background code that needs to update the user interface should be wrapped inside BeginInvokeOnMainThread. This is the equivalent of InvokeOnMainThread on iOS, RunOnUiThread on Android, and Dispatcher.BeginInvoke on Windows Phone.

The Xamarin.Forms code is:

Device.BeginInvokeOnMainThread ( () => {
  // interact with UI elements
});

Note that methods using async/await do not need to use BeginInvokeOnMainThread if they are running from the main UI thread.

Summary

The Xamarin.Forms Device class allows fine-grained control over functionality and layouts on a per-platform basis - even in common code (either PCL or Shared Projects).