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[操作系统]Xamarin.Android 的照相機使用


Android 提供了不少硬體功能。其中照相機功能更是兵家必爭之地。
甚至爆發如「三星門」等事件。不過本篇文章的目的只呼叫Android系統定義的API,取得相片後顯示出來。

現在我們先引入幾個 Android 負責處理 Camera 的命名空間。
當然會多些,不過要是在 Visual Studio 內開發的同學,很快就可以用工具移除。

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


我們先檢查硬體配備是否已準備好?

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

特別請大家注意

Intent intent = new Intent (MediaStore.ActionImageCapture);

在這邊我們使用系統提供的 Intent 來取得照相機的功能。

然後我們準備存儲目錄

private void CreateDirectoryForPictures (){  App._dir = new File (  Environment.GetExternalStoragePublicDirectory ( Environment.DirectoryPictures), "AndroidTips");  if (!App._dir.Exists ())  {    bool result =App._dir.Mkdirs( );    Debug.WriteLine ("mkdir:" + result);  }}   


準備處理 Bitmap 的方法(改變大小確保能按比例顯示)

public static class BitmapHelpers{  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);    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;  }}

 

準備回調的方法

protected override void OnActivityResult (int requestCode, Result resultCode, Intent data){  base.OnActivityResult (requestCode, resultCode, data);  // Make it available in the gallery  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 = resultImageView.Height ;  App.bitmap = App._file.Path.LoadAndResizeBitmap (width, height);  if (App.bitmap != null) {    resultImageView.SetImageBitmap (App.bitmap);    Debug.WriteLine ("contentUri:" + contentUri);    App.bitmap = null;  }  // Dispose of the Java side bitmap.  GC.Collect();}

 

如此即可快速調用照相機的功能。

參考資料:https://developer.xamarin.com/recipes/android/other_ux/camera_intent/take_a_picture_and_save_using_camera_app/