Xamarin.Essentials: Platform Extensions

Artikel
03/13/2019

Xamarin.Essentials provides several platform extension methods when having to work with platform types such as Rect, Size, and Point. This means that you can convert between the System version of these types for their iOS, Android, and UWP specific types.

Get started

To start using this API, read the getting started guide for Xamarin.Essentials to ensure the library is properly installed and set up in your projects.

Using Platform Extensions

Add a reference to Xamarin.Essentials in your class:

using Xamarin.Essentials;

All platform extensions can only be called from the iOS, Android, or UWP project.

Android Extensions

These extensions can only be accessed from an Android project.

Application Context & Activity

Using the platform extensions in the Platform class you can get access to the current Context or Activity for the running app.


var context = Platform.AppContext;

// Current Activity or null if not initialized or not started.
var activity = Platform.CurrentActivity;

If there is a situation where the Activity is needed, but the application hasn't fully started then the WaitForActivityAsync method should be used.

var activity = await Platform.WaitForActivityAsync();

Activity Lifecycle

In addition to getting the current Activity, you can also register for lifecycle events.

protected override void OnCreate(Bundle bundle)
{
    base.OnCreate(bundle);

    Xamarin.Essentials.Platform.Init(this, bundle);

    Xamarin.Essentials.Platform.ActivityStateChanged += Platform_ActivityStateChanged;
}

protected override void OnDestroy()
{
    base.OnDestroy();
    Xamarin.Essentials.Platform.ActivityStateChanged -= Platform_ActivityStateChanged;
}

void Platform_ActivityStateChanged(object sender, Xamarin.Essentials.ActivityStateChangedEventArgs e) =>
    Toast.MakeText(this, e.State.ToString(), ToastLength.Short).Show();

Activity states are the following:

Created
Resumed
Paused
Destroyed
SaveInstanceState
Started
Stopped

Read the Activity Lifecycle documentation to learn more.

iOS Extensions

These extensions can only be accessed from an iOS project.

Current UIViewController

Gain access to the currently visible UIViewController:

var vc = Platform.GetCurrentUIViewController();

This method will return null if unable to detect a UIViewController.

Cross-platform Extensions

These extensions exist in every platform.

Point

var system = new System.Drawing.Point(x, y);

// Convert to CoreGraphics.CGPoint, Android.Graphics.Point, and Windows.Foundation.Point
var platform = system.ToPlatformPoint();

// Back to System.Drawing.Point
var system2 = platform.ToSystemPoint();

Size

var system = new System.Drawing.Size(width, height);

// Convert to CoreGraphics.CGSize, Android.Util.Size, and Windows.Foundation.Size
var platform = system.ToPlatformSize();

// Back to System.Drawing.Size
var system2 = platform.ToSystemSize();

Rectangle

var system = new System.Drawing.Rectangle(x, y, width, height);

// Convert to CoreGraphics.CGRect, Android.Graphics.Rect, and Windows.Foundation.Rect
var platform = system.ToPlatformRectangle();

// Back to System.Drawing.Rectangle
var system2 = platform.ToSystemRectangle();

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