如何更正从 Android 设备捕获的图片的方向

此示例显示如何在 Android 设备上正确显示图像并将其显示。

首先，我们必须使用一个按钮和一个 imageview 创建示例应用程序。一旦用户点击按钮，相机就会启动，在用户选择图片后，它将以正确的方向显示在屏幕上。

1. 添加名为 TakePictureButton 的按钮和名为 TakenPictureImageView 的 imageview：

2. 现在打开活动代码：

这里首先参考你的控件：

ImageView _takenPictureImageView;
Button _takePictureButton;

    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.Main);

        _takenPictureImageView = FindViewById<ImageView>(Resource.Id.TakenPictureImageView);
        _takePictureButton = FindViewById<Button>(Resource.Id.TakePictureButton);

        _takePictureButton.Click += delegate 
        {
            takePicture();
        };
    }

3. 在我们的应用程序中，我们将使用 Components Store 中提供的 Xamarin Mobile 组件：

4. 将它添加到项目后，我们就可以继续了。添加以下代码，负责启动摄像头。应该在按钮单击中调用此方法，如上面的代码所示：

   void takePicture()
    {
        var picker = new MediaPicker(this);
        DateTime now = DateTime.Now;
        var intent = picker.GetTakePhotoUI(new StoreCameraMediaOptions
        {
            Name = "picture_" + now.Day + "_" + now.Month + "_" + now.Year + ".jpg",
            Directory = null
        });
        StartActivityForResult(intent, 1);
    }
   

5. 一旦用户拍照，我们应该以正确的方向显示它。要使用以下方法。它负责从拍摄的图像中检索 exif 信息（包括拍照期间的方向），而不是创建具有正确方向的位图：

   Bitmap loadAndResizeBitmap(string filePath)
    {
        BitmapFactory.Options options = new BitmapFactory.Options { InJustDecodeBounds = true };
        BitmapFactory.DecodeFile(filePath, options);
   
        int REQUIRED_SIZE = 100;
        int width_tmp = options.OutWidth, height_tmp = options.OutHeight;
        int scale = 4;
        while (true)
        {
            if (width_tmp / 2 < REQUIRED_SIZE || height_tmp / 2 < REQUIRED_SIZE)
                break;
            width_tmp /= 2;
            height_tmp /= 2;
            scale++;
        }
   
        options.InSampleSize = scale;
        options.InJustDecodeBounds = false;
        Bitmap resizedBitmap = BitmapFactory.DecodeFile(filePath, options);
   
        ExifInterface exif = null;
        try
        {
            exif = new ExifInterface(filePath);
            string orientation = exif.GetAttribute(ExifInterface.TagOrientation);
   
            Matrix matrix = new Matrix();
            switch (orientation)
            {
                case "1": // landscape
                    break;
                case "3":
                    matrix.PreRotate(180);
                    resizedBitmap = Bitmap.CreateBitmap(resizedBitmap, 0, 0, resizedBitmap.Width, resizedBitmap.Height, matrix, false);
                    matrix.Dispose();
                    matrix = null;
                    break;
                case "4":
                    matrix.PreRotate(180);
                    resizedBitmap = Bitmap.CreateBitmap(resizedBitmap, 0, 0, resizedBitmap.Width, resizedBitmap.Height, matrix, false);
                    matrix.Dispose();
                    matrix = null;
                    break;
                case "5":
                    matrix.PreRotate(90);
                    resizedBitmap = Bitmap.CreateBitmap(resizedBitmap, 0, 0, resizedBitmap.Width, resizedBitmap.Height, matrix, false);
                    matrix.Dispose();
                    matrix = null;
                    break;
                case "6": // portrait
                    matrix.PreRotate(90);
                    resizedBitmap = Bitmap.CreateBitmap(resizedBitmap, 0, 0, resizedBitmap.Width, resizedBitmap.Height, matrix, false);
                    matrix.Dispose();
                    matrix = null;
                    break;
                case "7":
                    matrix.PreRotate(-90);
                    resizedBitmap = Bitmap.CreateBitmap(resizedBitmap, 0, 0, resizedBitmap.Width, resizedBitmap.Height, matrix, false);
                    matrix.Dispose();
                    matrix = null;
                    break;
                case "8":
                    matrix.PreRotate(-90);
                    resizedBitmap = Bitmap.CreateBitmap(resizedBitmap, 0, 0, resizedBitmap.Width, resizedBitmap.Height, matrix, false);
                    matrix.Dispose();
                    matrix = null;
                    break;
            }
   
            return resizedBitmap;
        }
   
        catch (IOException ex)
        {
            Console.WriteLine("An exception was thrown when reading exif from media file...:" + ex.Message);
            return null;
        }
    }
   

6. 应该在用户拍照后调用的 OnActivityResult 方法中调用上面的方法：

   protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
    {
        base.OnActivityResult(requestCode, resultCode, data);
   
        if (requestCode == 1)
        {
            if (resultCode == Result.Ok)
            {
                data.GetMediaFileExtraAsync(this).ContinueWith(t =>
                {
                    using (Bitmap bmp = loadAndResizeBitmap(t.Result.Path))
                    {
                        if (bmp != null)
                        _takenPictureImageView.SetImageBitmap(bmp);
                    }
   
                }, TaskScheduler.FromCurrentSynchronizationContext());
            }
        }
    }
   

7. 启动应用程序。拍照看看结果：

http://i.stack.imgur.com/AFLk3.jpg http://i.stack.imgur.com/yU75s.jpg

而已。现在，你将以正确的方向显示所有拍摄的照片。