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Using Native Platform Features in Xamarin.Forms Through DependencyService

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Xamarin.Forms is platform-agnostic, and your single code base will work on all platforms. But if you want to perform platform-specific operations, you need to do some work, as Wei-Meng Lee shows.
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The beauty of Xamarin.Forms is that it's platform-agnostic. Creating a Xamarin.Forms project allows you to run the same code base on multiple platforms—iOS, Android, and Windows Phone. However, this platform-agnostic feature may pose problems if you need to access platform-specific services, such as location services, or speech-to-text services. Because Xamarin.Forms is focused on creating a unified UI for all platforms, it has no APIs for some services that native developers usually take for granted. Fortunately, Xamarin.Forms allows accesses to native APIs through the use of the DependencyService class.

The DependencyService class works using the following three-step process:

  1. Interface. The shared code defines an interface, which defines the functionality to be fulfilled by each platform.
  2. Registration. The platforms implement the interface defined by the shared code, and then register the classes so that DependencyService can create instances of the classes.
  3. Location. The shared code creates instances of the implemented classes in each platform, thereby allowing you to access the features of each platform.

In this article, I will walk you through an example to illustrate how you can access native features on each platform by using the DependencyService class.

Creating the Project

  1. Using Xamarin Studio, create a new Blank Xamarin.Forms App project (see Figure 1). Click Next.
  2. Figure 1 Selecting the Blank Xamarin.Forms App project template.

  3. Name the project UsingNativeFeatures and select the Use Portable Class Library option (see Figure 2). Click Next and then save the project.
  4. Figure 2 Naming the project.

Step 1: Defining the Interface

The first step in using the DependencyService class is to define an interface in the shared code. Follow these steps:

  1. Right-click your new UsingNativeFeatures project and select Add > New File (see Figure 3).
  2. Figure 3 Adding a new file to the project.

  3. Select General > Empty Interface and name it IMyInterface (see Figure 4). Click New.
  4. Figure 4 Adding an interface file to the project.

  5. Add the following statement in bold to the IMyInterface.cs file:
  6. using System;
    
    namespace UsingNativeFeatures
    {
        public interface IMyInterface
        {
            string GetPlatformName();
        }
    }

    IMyInterface now contains a method named GetPlatformName(), which returns a string.

Step 2: Registration of Shared Classes

Once the interface is defined, it is time to implement it on two platforms—iOS and Android.

  1. Add an Empty Class file to the UsingNativeFeatures.iOS project and name it PlatformDetails (see Figure 5).
  2. Figure 5 Adding a class file to the iOS project.

  3. Add the following statements in bold to the PlatformDetails.cs file:
  4. using System;
    using UsingNativeFeatures.iOS;
    [assembly: Xamarin.Forms.Dependency(typeof(PlatformDetails))]
    namespace UsingNativeFeatures.iOS
    {
        public class PlatformDetails: IMyInterface
        {
            public PlatformDetails () {}
    
            public string GetPlatformName() {
                return "I am iPhone!";
            }
        }
    }

    The PlatformDetails class implements the IMyInterface interface; the GetPlatformName() method simply returns the I am iPhone! string.

    The [assembly] attribute registers the PlatformDetails class as an implementation of the IMyInterface interface.

  5. Add an Empty Class file to the UsingNativeFeatures.Droid project and name it PlatformDetails (see Figure 6).
  6. Figure 6 Adding a class file to the Android project.

  7. Add the following statements in bold to the PlatformDetails.cs file:
  8. using System;
    using UsingNativeFeatures.Droid;
    [assembly: Xamarin.Forms.Dependency(typeof(PlatformDetails))]
    namespace UsingNativeFeatures.Droid
    {
        public class PlatformDetails: IMyInterface
        {
            public PlatformDetails () {}
    
            public string GetPlatformName() {
                return "I am Android!";
            }
        }
    }

    Here, the implementation is similar to the one for the iPhone, except that the GetPlatformName() method returns I am Android! as the string.

Step 3: Creating Instances for Each Location

Once the interface is implemented on the various platforms, it's time to use them in the shared code.

  1. Add the following statements in bold to the UsingNativeFeatures.cs file located in the UsingNativeFeatures project:
  2. using System;
    
    using Xamarin.Forms;
    
    namespace UsingNativeFeatures
    {
        public class App : Application
        {
            public App ()
            {
                //---get an instance of the implementation of the
                // IMyInterface---
                var platform = DependencyService.Get<IMyInterface> ();
    
                // The root page of your application
                MainPage = new ContentPage {
                    Content = new StackLayout {
                        VerticalOptions = LayoutOptions.Center,
                        Children = {
                            new Label {
                                XAlign = TextAlignment.Center,
                                //Text = "Welcome to Xamarin Forms!"
                                Text = platform.GetPlatformName()
                            }
                        }
                    }
                };
            }

    The DependencyService.Get<IMyInterface> statement allows you to get an instance of the implementation of the IMyInterface interface. Once this instance is obtained, you can call the GetPlatformName() method and set the Text property of the Label control to the string returned by each platform.

  3. Run the UsingNativeFeatures.iOS project on the iPhone 6 Simulator. The result should look like the one in Figure 7.
  4. Figure 7 Running the application on the iPhone Simulator.

  5. Run the UsingNativeFeatures.Droid project on an Android device. It should look like the result shown in Figure 8.
  6. Figure 8 Running the application on an Android device.

A More Detailed Example

The previous example demonstrated the design pattern for using the DependencyService class. Let's modify the example a little so that you can call some platform-specific APIs. Follow these steps:

  1. Add the following statement in bold to the IMyInterface.cs file:
  2. using System;
    
    namespace UsingNativeFeatures
    {
        public interface IMyInterface
        {
            string GetPlatformName();
            string GetDeviceName();
        }
    }

    The GetDeviceName() method returns the name of the device. You will need to implement this method in iOS and Android.

  3. Add the following statements in bold to the PlatformDetails.cs file in the UsingNativeFeatures.iOS project:
  4. using System;
    using UsingNativeFeatures.iOS;
    
    [assembly: Xamarin.Forms.Dependency(typeof(PlatformDetails))]
    namespace UsingNativeFeatures.iOS
    {
        public class PlatformDetails: IMyInterface
        {
            public PlatformDetails () {}
    
            public string GetPlatformName() {
                return "I am iPhone!";
            }
    
            public string GetDeviceName() {
                return UIKit.UIDevice.CurrentDevice.Name;
            }
        }
    }

    To get the name of the device in iOS, you use the UIDevice class in the UIKit Framework.

  5. Add the following statements in bold to the PlatformDetails.cs file located in the UsingNativeFeatures.Droid project:
  6. using System;
    using UsingNativeFeatures.Droid;
    
    using Android.Bluetooth;
    
    [assembly: Xamarin.Forms.Dependency(typeof(PlatformDetails))]
    namespace UsingNativeFeatures.Droid
    {
        public class PlatformDetails: IMyInterface
        {
            public PlatformDetails () {}
    
            public string GetPlatformName() {
                return "I am Android!";
            }
    
            public string GetDeviceName() {
                BluetoothAdapter myDevice =
                    BluetoothAdapter.DefaultAdapter;
                return myDevice.Name;
            }
        }
    }

    Getting the device name is a little tricky in Android, which has no public API for that purpose. You can get it from the BluetoothAdapter class; however, to use the BluetoothAdapter class, you need to add the Bluetooth permission in the UsingNativeFeatures.Droid project.

  7. Double-click the UsingNativeFeatures.Droid project and select Android Application (see Figure 9). Select the Bluetooth permission.
  8. Figure 9 Adding the Bluetooth permission to the project.

  9. Add the following statement in bold to the UsingNativeFeature.cs file in the UsingNativeFeatures project:
  10. public App ()
    {
    
        var platform = DependencyService.Get<IMyInterface> ();
    
        // The root page of your application
        MainPage = new ContentPage {
            Content = new StackLayout {
                VerticalOptions = LayoutOptions.Center,
                Children = {
                    new Label {
                        XAlign = TextAlignment.Center,
                        //Text = "Welcome to Xamarin Forms!"
                        //Text = platform.GetPlatformName()
                        Text = platform.GetDeviceName()
                    }
                }
            }
        };
    }
  11. Run the applications on both the iPhone Simulator and a real Android device. Figure 10 shows the output.
  12. Figure 10 Viewing the output on the iPhone Simulator and an Android device.

Summary

In this article, you learned how Xamarin.Forms allows you to access native features on each platform by using the DependencyService class. You first define the interface in the shared code so that you can implement the required feature in each platform. Once you have implemented the interface in each platform, the shared code can call the methods of the implemented class and access the features natively on each platform.

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