Xamarin Forms Creating And Using Dependency Services Complete Guide

Xamarin.Forms Creating and Using Dependency Services

Key Points

1. Purpose: Dependency services abstract the platform-specific implementations of specific functionalities such as accessing the file system, launching the camera, making network requests, vibration, and more.

2. Implementation Steps:

   • Define an Interface: Create an interface that outlines the methods you need to use across all platforms.
   • Implement Each Platform: Provide platform-specific implementations for those methods.
   • Register Implementations: Register these implementations with Xamarin.Forms.
   • Consume the Service: Use constructor injection or method calls to consume these services in your Xamarin.Forms code.

3. Lifecycle:

   • Initialization: Dependency services are initialized once when first used.
   • Use Across Platforms: They can be used anywhere in your shared Xamarin.Forms project after registration.

4. Constructor Injection:

   • Preferred Method: Use constructor injection (also known as Dependency Injection) to integrate dependency services. This improves the readability of your code and makes it easier to test.

5. Error Handling:

   • Cross-Platform: Handle exceptions consistently across platforms by implementing appropriate checks in your shared logic and handling them through try-catch blocks.
   • Platform-Specific: Use platform-specific error handling mechanisms when necessary to manage unique exceptions on each platform.

6. Performance Considerations:

   • Minimize Overhead: Avoid unnecessary cross-platform communication to minimize performance costs.
   • Caching: Cache results of complex computations if they don’t change frequently, reducing the load on performance-critical areas of your application.

7. Debugging Tips:

   • Check Registration: Ensure that all platform implementations are correctly registered with the DependencyService.
   • Use Logs: Implement logging to trace method calls and catch errors where methods fail to execute as expected.

8. Documentation and Maintenance:

   • Documentation: Keep clear documentation for the interface and its implementations. This eases troubleshooting when issues arise.
   • Refactoring: Regularly refactor your code to keep it maintainable. Consider splitting large interfaces into smaller ones if they become unwieldy.

Step-by-Step Guide

Step 1: Define an Interface

public interface INetworkService
{
    bool IsConnected { get; }
}

Step 2: Implement Each Platform

• Android Implementation

using Android.Net;
using Xamarin.Forms;

[assembly: Dependency(typeof(NetworkServiceAndroid))]
public class NetworkServiceAndroid : INetworkService
{
    public bool IsConnected => Connectivity.NetworkInfo != null && Connectivity.NetworkInfo.IsConnected;
}

• iOS Implementation

using Foundation;
using UIKit;
using Xamarin.Forms;

[assembly: Dependency(typeof(NetworkServiceiOS))]
public class NetworkServiceiOS : INetworkService
{
    public bool IsConnected => UIApplication.SharedApplication.NetworkActivityIndicatorVisible;
}

• UWP Implementation

using Windows.Networking.Connectivity;
using Xamarin.Forms;

[assembly: Dependency(typeof(NetworkServiceUWP))]
public class NetworkServiceUWP : INetworkService
{
    public bool IsConnected => NetworkInformation.GetInternetConnectionProfile()?.GetNetworkConnectivityLevel() ==
                             NetworkConnectivityLevel.InternetAccess;
}

Step 3: Register Implementations The assembly: Dependency attribute registers the implementation as a service.

Step 4: Consume the Service You can consume dependency services via constructor injection or method calls.

• Constructor Injection

public class MyPageViewModel
{
    private readonly INetworkService _networkService;
    
    public MyPageViewModel(INetworkService networkService)
    {
        _networkService = networkService ?? throw new ArgumentNullException(nameof(networkService));
    }

    public void CheckNetworkConnection()
    {
        var isConnected = _networkService.IsConnected;
        // Do something with 'isConnected'
    }
}

• Method Call

public void CheckNetworkConnection()
{
    var networkService = DependencyService.Get<INetworkService>();
    var isConnected = networkService.IsConnected;
    // Do something with 'isConnected'
}

Important Information

• Resolution Failures: If the dependency service cannot resolve a platform-specific implementation, it will throw a NullReferenceException. To avoid this, make sure every platform has an implementation registered.

• Version Differences: Be aware that certain APIs may differ between versions of the target platforms (e.g., iOS 13 vs. iOS 14). Always test your dependency services on multiple versions of your target platforms.

• Testing: To unit test your shared code, mock the dependency services. Use a testing framework like Moq in C# to create mock objects that simulate behavior without depending on actual platform implementations.

• Asynchronous Operations: Many platform APIs require asynchronous operations (e.g., file I/O, network requests). Always ensure that your dependency services return tasks for operations that take time or may need to be awaited.

• Performance Tuning: If profiling indicates that a particular dependency service is slowing down performance, consider optimizing the underlying API calls or exploring alternative methods for achieving the same functionality.

• NuGet Packages: Sometimes, functionalities are available via NuGet packages. These packages may provide a higher level of abstraction and better handling across different platforms, saving you from reinventing the wheel.