How i take a picture without the camera preview?

UmCaraQualquer · January 2020

in short, I am making an application that if someone touches my cell phone, it sends a log to my computer, this log includes the date, time and 2 photos. I want my application to take 2 photos, one from the front camera and one from the rear camera, but how do I do that without the photo preview? I can't tell anyone on my cell phone "take a picture there for me". And, I have to do this all in the "OnPasswordFailed" and "OnPasswordSucceeded" methods of DeviceAdminReceiver, that is, in no screen, everything in the background. Is it possible to take a picture without a preview, in the background?

Actually, my code to take a picture is:

var p = await CrossMedia.Current.TakePhotoAsync(new StoreCameraMediaOptions
{
    DefaultCamera = CameraDevice.Front
});

LeonLu · January 2020

Do you want to achieve the result like following GIF?

You cannot use CrossMedia this plugin to achieve it. you should use Native Camera API to achieve it.

I used the SurfaceView to achieve it, but I set the layout_height and layout_width to 1dp. it cannot be seen in the activity.

Here is background code.

     [Activity(Label = "@string/app_name", Theme = "@style/AppTheme", MainLauncher = true)]
public class MainActivity : AppCompatActivity, ISurfaceHolderCallback
{
    private LinearLayout mll;
    private Button button;
    private Camera camera;
    private ISurfaceHolder mHolder;
    private SurfaceView sfv;
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        Xamarin.Essentials.Platform.Init(this, savedInstanceState);
        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.activity_main);


       // Android.Content.PM.ShortcutManager shortcutManager = (ShortcutManager)this.GetSystemService(Context.ShortcutService);

        //Open camera permission
        //if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.Camera) != (int)Android.Content.PM.Permission.Granted)
        //{
        //  RequestPermissions(new string[] { Manifest.Permission.Camera }, 0);
        //}


        ////Open storage permission
        //if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.WriteExternalStorage) != (int)Android.Content.PM.Permission.Granted)
        //{
        //  RequestPermissions(new string[] { Manifest.Permission.ReadExternalStorage, Manifest.Permission.WriteExternalStorage }, 0);
        //}


         initView();
        initListener();

}
    protected override void OnResume()
    {
        base.OnResume();
        if (null == camera)
        {
            camera = getCustomCamera();
            if (mHolder != null)
            {
                previceCamera(camera, mHolder);
            }

        }

    }

    protected override void OnStop()
    {
        base.OnStop();
        if (null != camera)
        {
            camera.SetPreviewCallback(null);
            camera.StopPreview();
            camera.Release();
            camera = null;
        }

    }
    private void previceCamera(Camera camera, ISurfaceHolder mHolder)
    {
        camera.SetPreviewDisplay(mHolder);
        camera.SetDisplayOrientation(90);
        camera.StartPreview();
    }


    private int FindFrontFacingCamera()
    {
        int cameraId = -1;
        // Search for the front facing camera

        int numberOfCameras = Camera.NumberOfCameras;
        for (int i = 0; i < numberOfCameras; i++)
        {
            CameraInfo info = new CameraInfo();
            Camera.GetCameraInfo(i, info);
            if (info.Facing == CameraInfo.CameraFacingFront)
            {
                //Log.d(DEBUG_TAG, "Camera found");
                cameraId = i;
                break;
            }
        }
        return cameraId;
    }

    private Camera getCustomCamera()
    {
        if (null == camera)
        {
            camera = Camera.Open(FindFrontFacingCamera());
            // CameraInfo cameraInfo = new CameraInfo();  

        }
        return camera;

    }

    private void initListener()
    {
        button.Click += Button_Click; 
    }

    private void Button_Click(object sender, System.EventArgs e)
    {
        var parameters = camera.GetParameters();

        parameters.PictureFormat = ImageFormatType.Jpeg;
        parameters.SetPreviewSize(480, 720);
        parameters.FocusMode = Camera.Parameters.FocusModeAuto;
        camera.AutoFocus(new MyFocusCallback(camera));
    }




    private void initView()
    {
        mll = FindViewById<LinearLayout>(Resource.Id.ll);
        button = FindViewById<Button>(Resource.Id.button1);
        mFloatView();
        mHolder = sfv.Holder;
        mHolder.AddCallback(this);
    }

    public void mFloatView()
    {

        IWindowManager windowManager = GetSystemService(Context.WindowService).JavaCast<IWindowManager>();
        WindowManagerFlags flags = WindowManagerFlags.NotFocusable | WindowManagerFlags.NotTouchModal | 
        WindowManagerFlags.NotTouchable;
        var layoutParams = new WindowManagerLayoutParams(1, 1,
        WindowManagerTypes.SystemAlert,
        flags,
        Format.Rgb888);
        sfv = new SurfaceView(this);
        //mll is LinearLayout
        mll.AddView(sfv, layoutParams);

    }



    public void SurfaceCreated(ISurfaceHolder holder)
    {
        previceCamera(camera, holder);
    }

    public void SurfaceDestroyed(ISurfaceHolder holder)
    {
        if (null != camera)
        {
            camera.SetPreviewCallback(null);
            camera.StopPreview();
            camera.Release();
            camera = null;
        }


    }

    public void SurfaceChanged(ISurfaceHolder holder, [GeneratedEnum] Format format, int width, int height)
    {
        camera.StopPreview();
        previceCamera(camera, holder);
    }



    public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] 
   Android.Content.PM.Permission[] grantResults)
    {
        PermissionsImplementation.Current.OnRequestPermissionsResult(requestCode, permissions, grantResults);


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

public class MyFocusCallback : Java.Lang.Object, IAutoFocusCallback
{
    Camera mCamera;
    public MyFocusCallback(Camera camera)
    {
        mCamera = camera;
    }
    public void Dispose()
    {
    }

    public void OnAutoFocus(bool success, Camera camera)
    {
    mCamera.TakePicture(null, null, new MyPictureCallback());
    if (success)
        {

        }
    }
}

public class MyPictureCallback : Java.Lang.Object, IPictureCallback
{

    public void Dispose()
    {
        throw new NotImplementedException();
    }

    public void OnPictureTaken(byte[] data, Camera camera)
    {
        dealWithCameraData(data);
    }

    private void dealWithCameraData(byte[] data)
    {
        // Here to save your photo
        FileOutputStream fos = null;
    //       string tempStr = System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal);
    var path = 

 Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDocuments).AbsolutePath;
    string fileName = path + Java.Lang.JavaSystem.CurrentTimeMillis() + ".jpg";

       Toast.MakeText(Application.Context,fileName,ToastLength.Short).Show();
        File tempFile = new File(fileName);
        fos = new FileOutputStream(fileName);
        fos.Write(data);
        fos.Close();

    }
}

Here is my demo(Do not forget to add the permissions manually).

UmCaraQualquer · January 2020

I will take a picture in the DeviceAdminReceiver, i don't have an activity or a button.

LeonLu · January 2020

This is just a simple for your function(withOut button and activity, I cannot test it for you), You can create surfaceview by code in background service or broadCastReceiver.

Ruvi1996 · June 2020

Hi @LeonLu I am a beginner. But I want to achieve what you have done there. Can you please help me?

matute · July 2020

getting System.NullReferenceException: 'Object reference not set to an instance of an object.'
in line var parameters = camera.GetParameters();

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