[Activity(Label = "@string/app_name", Theme = "@style/AppTheme.NoActionBar", MainLauncher = true)]
    public class MainActivity : AppCompatActivity
    {

        public const  int TAKE_PHOTO = 1;//声明一个请求码，用于识别返回的结果
        private ImageView picture;
        private Android.Net.Uri imageUri;
        private Button CaptureButton;
        private String filePath = Android.OS.Environment.ExternalStorageDirectory + File.Separator + "output_image.jpg";

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            Xamarin.Essentials.Platform.Init(this, savedInstanceState);
            SetContentView(Resource.Layout.activity_main);


            RequestPermissions(LuoPermission.LuoPermissionList, 0);
            CaptureButton = (Button)FindViewById(Resource.Id.take_photo);
            picture = (ImageView)FindViewById(Resource.Id.picture);

            CaptureButton.Click += (object sender, System.EventArgs e) =>
            {
                TakePhoto();
            };

            SetDefualtImage();



        }
        public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Permission[] grantResults)
        {
            Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

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


        void TakePhoto()
        {
            requestPermission();

        }

        //动态请求权限
        private void requestPermission()
        {

            if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.WriteExternalStorage) != Permission.Granted)
            {
                //请求权限
                ActivityCompat.RequestPermissions(this, new String[] { Manifest.Permission.WriteExternalStorage, Manifest.Permission.Camera }, 1);
            }
            else
            {
                //调用
                requestCamera();
            }
        }
        private void requestCamera()
        {
            File outputImage = new File(filePath);
            /*
            创建一个File文件对象，用于存放摄像头拍下的图片，我们把这个图片命名为output_image.jpg
            并把它存放在应用关联缓存目录下，调用getExternalCacheDir()可以得到这个目录，为什么要
            用关联缓存目录呢？由于android6.0开始，读写sd卡列为了危险权限，使用的时候必须要有权限，
            应用关联目录则可以跳过这一步
             */
            try//判断图片是否存在，存在则删除在创建，不存在则直接创建
            {
                if (!outputImage.ParentFile.Exists())
                {
                    outputImage.ParentFile.Mkdirs();
                }
                if (outputImage.Exists())
                {
                    outputImage.Delete();
                }

                outputImage.CreateNewFile();

                if (Build.VERSION.SdkInt >= (BuildVersionCodes)24)
                {
                    imageUri = FileProvider.GetUriForFile(this,
                            "com.example.mydemo.fileprovider", outputImage);
                }
                else
                {
                    imageUri = Android.Net.Uri.FromFile(outputImage);
                }
                
                //使用隐示的Intent，系统会找到与它对应的活动，即调用摄像头，并把它存储
                Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
                intent.PutExtra(MediaStore.ExtraOutput, imageUri);
                StartActivityForResult(intent, TAKE_PHOTO);
                //调用会返回结果的开启方式，返回成功的话，则把它显示出来


              
            }
            catch (IOException e)
            {
                e.PrintStackTrace();
            }

        }

        protected override void OnActivityResult(int requestCode, [GeneratedEnum] Result resultCode, Intent data)
        {
            base.OnActivityResult(requestCode, resultCode, data);
            switch (requestCode)
            {
                case TAKE_PHOTO:
                    if (resultCode ==  Result.Ok)
                    {
                        try
                        {

                            Bitmap bitmap = BitmapFactory.DecodeStream(ContentResolver.OpenInputStream(imageUri));
                            picture.SetImageBitmap(bitmap);
                            //将图片解析成Bitmap对象，并把它显现出来
                        }
                        catch (FileNotFoundException e)
                        {
                            e.PrintStackTrace();
                        }
                    }
                    break;
                default:
                    break;
            }
        }

        //处理返回结果的函数，下面是隐示Intent的返回结果的处理方式，具体见以前我所发的intent讲解
        public override void OnActivityReenter(int resultCode, Intent data)
        {
            base.OnActivityReenter(resultCode, data);
            
        }

    

        //设置保存拍照图片——>再次关闭app重新打开显示为上次拍照照片
        private void SetDefualtImage()
        {
            File outputImage = new File(filePath);
            if (!outputImage.Exists())
            {
                return;
            }
            picture.SetImageBitmap(BitmapFactory.DecodeFile(filePath));
        }





    }