如何调整 xamarin.forms 中的图像大小？

Question

我正在研究 xamarin.forms。我必须从图库中选择图像，然后调整它们的大小，然后将它们上传到服务器上。但我不知道如何以给定的特定尺寸调整所选图像的大小？ 请告诉我我该怎么做？

Answer 1

这可以与流（如果您使用媒体插件https://github.com/jamesmontemagno/MediaPlugin）或标准字节数组一起使用。

// If you already have the byte[]
byte[] resizedImage = await CrossImageResizer.Current.ResizeImageWithAspectRatioAsync(originalImageBytes, 500, 1000);

// If you have a stream, such as:
// var file = await CrossMedia.Current.PickPhotoAsync(options);
// var originalImageStream = file.GetStream();
byte[] resizedImage = await CrossImageResizer.Current.ResizeImageWithAspectRatioAsync(originalImageStream, 500, 1000);

Answer 2

我尝试使用CrossImageResizer.Current...，但在Media Plugin 中没有找到它。相反，我发现了一个名为 MaxWidthHeight 的选项，它仅在您还添加 PhotoSize = PhotoSize.MaxWidthHeight 选项时才有效。

例如：

 var file = await CrossMedia.Current.PickPhotoAsync(new PickMediaOptions() { PhotoSize = PhotoSize.MaxWidthHeight, MaxWidthHeight = 600 });
 var file = await CrossMedia.Current.TakePhotoAsync(new StoreCameraMediaOptions { PhotoSize = PhotoSize.MaxWidthHeight, MaxWidthHeight = 600 });

Answer 3

可悲的是，没有一个好的跨平台图像调整器（我在发这篇文章时发现的）。图像处理并非真正设计为在 iOS 和 Android 的跨平台环境中进行。使用特定于平台的代码在每个平台上执行此操作会更快、更清晰。您可以使用依赖注入和 DependencyService（或任何其他服务或 IOC）来做到这一点。

AdamP 对如何做到这一点给出了很好的回应Platform Specific Image Resizing

Answer 4

这是从上面链接中获取的代码。

iOS

public class MediaService : IMediaService
{

    public byte[] ResizeImage(byte[] imageData, float width, float height)
    {

        UIImage originalImage = ImageFromByteArray(imageData);

        var originalHeight = originalImage.Size.Height;
        var originalWidth = originalImage.Size.Width;

        nfloat newHeight = 0;
        nfloat newWidth = 0;

        if (originalHeight > originalWidth)
        {
            newHeight = height;
            nfloat ratio = originalHeight / height;
            newWidth = originalWidth / ratio;
        }
        else 
        {
            newWidth = width;
            nfloat ratio = originalWidth / width;
            newHeight = originalHeight / ratio;
        }

        width = (float)newWidth;
        height = (float)newHeight;

        UIGraphics.BeginImageContext(new SizeF(width, height));
        originalImage.Draw(new RectangleF(0, 0, width, height));
        var resizedImage = UIGraphics.GetImageFromCurrentImageContext();
        UIGraphics.EndImageContext();

        var bytesImagen = resizedImage.AsJPEG().ToArray();
        resizedImage.Dispose();
        return bytesImagen;
   }          
}

安卓

public class MediaService : IMediaService
{

    public byte[] ResizeImage(byte[] imageData, float width, float height)
    {
        // Load the bitmap 
        BitmapFactory.Options options = new BitmapFactory.Options();// Create object of bitmapfactory's option method for further option use
        options.InPurgeable = true; // inPurgeable is used to free up memory while required
        Bitmap originalImage = BitmapFactory.DecodeByteArray(imageData, 0, imageData.Length, options);

        float newHeight = 0;
        float newWidth = 0;

        var originalHeight = originalImage.Height;
        var originalWidth = originalImage.Width;

        if (originalHeight > originalWidth)
        {
            newHeight = height;
            float ratio = originalHeight / height;
            newWidth = originalWidth / ratio;
        }
        else 
        {
            newWidth = width;
            float ratio = originalWidth / width;
            newHeight = originalHeight / ratio;
        }

        Bitmap resizedImage = Bitmap.CreateScaledBitmap(originalImage, (int)newWidth, (int)newHeight, true);

        originalImage.Recycle();

        using (MemoryStream ms = new MemoryStream())
        {
            resizedImage.Compress(Bitmap.CompressFormat.Png, 100, ms);

            resizedImage.Recycle();

            return ms.ToArray();
        }
    }

WinPhone

public class MediaService : IMediaService
{
    private MediaImplementation mi = new MediaImplementation();

    public byte[] ResizeImage(byte[] imageData, float width, float height)
    {
        byte[] resizedData;

        using (MemoryStream streamIn = new MemoryStream(imageData))
        {
            WriteableBitmap bitmap = PictureDecoder.DecodeJpeg(streamIn, (int)width, (int)height);

            float Height = 0;
            float Width = 0;

            float originalHeight = bitmap.PixelHeight;
            float originalWidth = bitmap.PixelWidth;

            if (originalHeight > originalWidth)
            {
                Height = height;
                float ratio = originalHeight / height;
                Width = originalWidth / ratio;
            }
            else
            {
                Width = width;
                float ratio = originalWidth / width;
                Height = originalHeight / ratio;
            }

            using (MemoryStream streamOut = new MemoryStream())
            {
                bitmap.SaveJpeg(streamOut, (int)Width, (int)Height, 0, 100);
                resizedData = streamOut.ToArray();
            }
        }
        return resizedData;
    }
}

编辑：如果您已经在项目中使用 FFImageLoading，那么您可以将其用于您的平台。

https://github.com/luberda-molinet/FFImageLoading