如何在Xamarin Forms应用程序中拦截Android设备音量上/下按钮以打开相机？

我正在开发一个Xamarin Forms应用程序，它使用蓝牙快门点击器来拍照。目前，蓝牙快门在被点击时会激活音量上/下按钮。我正在尝试拦截音量按钮，这样我就可以在点击点击器时打开设备相机。
我正在尝试让Android版本工作。我可以在我的MainActivity.cs文件中成功拦截Android代码中的音量按钮。我想我必须使用依赖服务，以便音量按钮触发CameraButton_Clicked事件，但我不知道如何正确地进行这项工作。任何帮助都将非常感谢。

主要活动.CS：

//override the volume up/down buttons for bluetooth shutter clicker
        public override bool OnKeyUp(Keycode keyCode, KeyEvent e)
        {
            if (keyCode == Keycode.VolumeDown)
            {
                return true;
            }

            if (keyCode == Keycode.VolumeUp)
            {
                return true;
            }
            return base.OnKeyUp(keyCode, e);
        }
        public override bool OnKeyDown(Keycode keyCode, KeyEvent e)
        {
            if (keyCode == Keycode.VolumeDown)
            {
                return true;
            }

            if (keyCode == Keycode.VolumeUp)
            {
                return true;
            }
            return base.OnKeyDown(keyCode, e);
        }

接口：

namespace MyApp
{
    public interface IBluetoothClicker 
    {
       object GetVolumeOverride();

    }
}

蓝牙遥控器_机器人.cs：

[assembly: Xamarin.Forms.Dependency (typeof (BluetoothClicker_Droid))]
namespace MyApp.Droid
{
    public class BluetoothClicker_Droid: IBluetoothClicker
    {

        public BluetoothClicker_Droid ()
        {
        }

        public object GetVolumeOverride()
        {         
            //CameraButton_Clicked = true;

            return true;

        }
    }
}

照相机页面.xaml.cs：

public CameraPage()
        {
            InitializeComponent();

            CameraImage.Source = "CameraImage.png";
            TakePhotoButton.Clicked += CameraButton_Clicked; //opens camera

            Func<object> func = () =>
            {
                var obj = DependencyService.Get<IBluetoothClicker>().GetVolumeOverride();
                //obj += CameraButton_Clicked;
                return obj;
            };
        }

If you just want to achieve that in android. you could open the camera directly like following GIF.

You can take a photo in android, Then use message center to upload your image in PCL like followcode.
MainPage.xaml.cs

public partial class MainPage : ContentPage
{
    public MainPage()
    {
        InitializeComponent();

        CameraImage.Source = "CameraImage.png";

        MessagingCenter.Subscribe<App, string>(App.Current, "OpenPage", (snd, arg) =>
        {
            Device.BeginInvokeOnMainThread(() => {
                CameraImage.Source = arg;
            });
        });
    }   
}

MainActivity.cs

public static class App_test
{
    public static File _file;
    public static File _dir;
    public static Bitmap bitmap;
}

[Activity(Label = "InterceptButton", Icon = "@mipmap/icon", Theme = "@style/MainTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        StrictMode.VmPolicy.Builder builder = new StrictMode.VmPolicy.Builder();
        StrictMode.SetVmPolicy(builder.Build());
        TabLayoutResource = Resource.Layout.Tabbar;
        ToolbarResource = Resource.Layout.Toolbar;

        base.OnCreate(savedInstanceState);

        Xamarin.Essentials.Platform.Init(this, savedInstanceState);
        global::Xamarin.Forms.Forms.Init(this, savedInstanceState);

        LoadApplication(new App());

        if (IsThereAnAppToTakePictures())
        {
            CreateDirectoryForPictures();
        }
    }
    public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
    {
        Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

        base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
    }

    public override bool OnKeyUp([GeneratedEnum] Keycode keyCode, KeyEvent e)
    {
        if (keyCode == Keycode.VolumeDown)
        {
            Toast.MakeText(this, "OnKeyUp-VolumeDown", ToastLength.Short).Show();

            return true;
        }

        if (keyCode == Keycode.VolumeUp)
        {
          //  Toast.MakeText(this, "OnKeyUp-VolumeUp", ToastLength.Short).Show();
            return true;
        }

        return base.OnKeyUp(keyCode, e);
    }
    public override bool OnKeyDown([GeneratedEnum] Keycode keyCode, KeyEvent e)
    {
        if (keyCode == Keycode.VolumeDown)
        {
            Toast.MakeText(this, "OnKeyDown-VolumeDown", ToastLength.Short).Show();
            return true;
        }

        if (keyCode == Keycode.VolumeUp)
        {
            Intent intent = new Intent(MediaStore.ActionImageCapture);
               App_test._file = new File(App_test._dir, String.Format("myPhoto_{0}.jpg", Guid.NewGuid()));
               intent.PutExtra(MediaStore.ExtraOutput, Uri.FromFile(App_test._file));
            StartActivityForResult(intent, 0);
            Toast.MakeText(this, "OnKeyDown-VolumeUp", ToastLength.Short).Show();
            return true;
        }
        return base.OnKeyDown(keyCode, e);
    }

    protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
    {
        base.OnActivityResult(requestCode, resultCode, data);
        Intent mediaScanIntent = new Intent(Intent.ActionMediaScannerScanFile);
        Uri contentUri = Uri.FromFile(App_test._file);
        mediaScanIntent.SetData(contentUri);
        SendBroadcast(mediaScanIntent);

        App_test.bitmap = App_test._file.Path.LoadAndResizeBitmap(100, 100);
       string path= App_test._file.Path;
        if (App_test.bitmap != null)
        {
            MessagingCenter.Send<App, string>(App.Current as App, "OpenPage", path);

            App_test.bitmap = null;
        }
        GC.Collect();
    }

    private void CreateDirectoryForPictures()
    {
        App_test._dir = new File(
            Environment.GetExternalStoragePublicDirectory(
                Environment.DirectoryPictures), "CameraAppDemo");
        if (!App_test._dir.Exists())
        {
            App_test._dir.Mkdirs();
        }
    }

    private bool IsThereAnAppToTakePictures()
    {
        Intent intent = new Intent(MediaStore.ActionImageCapture);
        IList<ResolveInfo> availableActivities =
            PackageManager.QueryIntentActivities(intent, PackageInfoFlags.MatchDefaultOnly);
        return availableActivities != null && availableActivities.Count > 0;
    }
}

So I do not know why you want to use DependencyService .Maybe you have better ways to achieve that.
There is my demo. I used VS 2019, it will make some difference If you used VS 2017.
https://github.com/851265601/InterceptButton

如何在Xamarin Forms应用程序中拦截Android设备音量上/下按钮以打开相机？

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