using System;
    using System.Collections.Generic;
    using Android.App;
    using Android.Content;
    using Android.Content.PM;
    using Android.Graphics;
    using Android.OS;
    using Android.Provider;
    using Android.Widget;
    using Java.IO;
    using Environment = Android.OS.Environment;
    using Uri = Android.Net.Uri; 

　　　　 protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);
            SetContentView(Resource.Layout.Main);
             
            if (IsThereAnAppToTakePictures())   //判断本设备是否存在拍照功能
            {
                CreateDirectoryForPictures();

                Button button = FindViewById<Button>(Resource.Id.myButton);
                _imageView = FindViewById<ImageView>(Resource.Id.imageView1);
                button.Click += TakeAPicture;
            } 
        }

        /// <summary>
        ///  判断是否具备拍照功能
        /// </summary>
        /// <returns></returns>
        private bool IsThereAnAppToTakePictures()
        {
            Intent intent = new Intent(MediaStore.ActionImageCapture);
            IList<ResolveInfo> availableActivities =
                PackageManager.QueryIntentActivities(intent, PackageInfoFlags.MatchDefaultOnly);
            return availableActivities != null && availableActivities.Count > 0;
        }     

        /// <summary>
        /// 创建目录图片
        /// </summary> 
        private void CreateDirectoryForPictures()
        {
            App._dir = new File(
                Environment.GetExternalStoragePublicDirectory(
                    Environment.DirectoryPictures), "CameraAppDemo");        //CameraAppDemo
            if (!App._dir.Exists())
            {
                App._dir.Mkdirs();
            }
        }

        /// <summary>
        /// 拍照
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="eventArgs"></param>
        private void TakeAPicture(object sender, EventArgs eventArgs)
        {
            Intent intent = new Intent(MediaStore.ActionImageCapture);

            App._file = new File(App._dir, String.Format("myPhoto_{0}.jpg", Guid.NewGuid()));       //保存路径

            intent.PutExtra(MediaStore.ExtraOutput, Uri.FromFile(App._file));

            StartActivityForResult(intent, 0);
        }

        /// <summary>
        /// 拍照结束执行
        /// </summary>
        /// <param name="requestCode"></param>
        /// <param name="resultCode"></param>
        /// <param name="data"></param>
        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._file);
            mediaScanIntent.SetData(contentUri);
            SendBroadcast(mediaScanIntent);

            // Display in ImageView. We will resize the bitmap to fit the display
            // Loading the full sized image will consume to much memory 
            // and cause the application to crash.

            int height = Resources.DisplayMetrics.HeightPixels;
            int width = _imageView.Height;

            //获取拍照的位图
            App.bitmap = App._file.Path.LoadAndResizeBitmap(width, height);
            if (App.bitmap != null)
            {
                //将图片绑定到控件上
                _imageView.SetImageBitmap(App.bitmap); 

                //清空bitmap 否则会出现oom问题
                App.bitmap = null;
            }

            // Dispose of the Java side bitmap.
            GC.Collect();
        }

        public static Bitmap LoadAndResizeBitmap(this string fileName, int width, int height)
        {
            // First we get the the dimensions of the file on disk
            BitmapFactory.Options options = new BitmapFactory.Options { InJustDecodeBounds = true };
            BitmapFactory.DecodeFile(fileName, options);

            // Next we calculate the ratio that we need to resize the image by
            // in order to fit the requested dimensions.
            int outHeight = options.OutHeight;
            int outWidth = options.OutWidth;
            int inSampleSize = 1;

            if (outHeight > height || outWidth > width)
            {
                inSampleSize = outWidth > outHeight
                                   ? outHeight / height
                                   : outWidth / width;
            }

            // Now we will load the image and have BitmapFactory resize it for us.
            options.InSampleSize = inSampleSize;
            options.InJustDecodeBounds = false;
            Bitmap resizedBitmap = BitmapFactory.DecodeFile(fileName, options);

            return resizedBitmap;
        }

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