How to load/draw an image using NGraphics? - xamarin

Question

In my Xamarin Forms app, I have an image under androidProject/Resources/drawable/myImage.png. To load these from Xamarin, you can simply do
Image myImage = new Image() { Source = ImageSource.FromFile("myImage.png") };
However, there is no way to draw an Image using NGraphics. Instead, NGraphics DrawImage(IImage) requires an IImage. As far as I can tell, there's no way to turn a Xamarin.Forms.Image into an NGraphics.IImage. In fact, the only way I could find to load IImage is
IImage myImage = Platform.LoadImage("myImage.png");
However, this doesn't work because under the hood this uses BitmapFactory.decodeFile(), which requires the absolute file path. And I couldn't find any way to get the absolute file path of a resource (if it even exists?)
So, how do I actually load and display an image using NGraphics?

Answer 1

NGraphics does not provide any helpers to load images from your Platforms Resource files.
You could do something as follows. However, it will add some overhead converting back and forth between bitmap -> stream -> bitmap.
Android:
Stream GetDrawableStream(Context context, int resourceId)
{
var drawable = ResourcesCompat.GetDrawable(context.Resources, resourceId, context.Theme);
if (drawable is BitmapDrawable bitmapDrawable)
{
var stream = new MemoryStream();
var bitmap = bitmapDrawable.Bitmap;
bitmap.Compress(Bitmap.CompressFormat.Png, 80, stream);
bitmap.Recycle();
return stream;
}
return null;
}
iOS:
Stream GetImageStream(string fileName)
{
using (var image = UIImage.FromFile(fileName))
using (var imageData = image.AsPNG())
{
var byteArray = new byte[imageData.Length];
System.Runtime.InteropServices.Marshal.Copy(imageData.Bytes, byteArray, 0, Convert.ToInt32(imageData.Length));
var stream = new MemoryStream(byteArray);
return stream;
}
return null;
}
However, you could go directly from Bitmap to BitmapImage on Android instead like:
BitmapImage GetBitmapFromDrawable(Context context, int resourceId)
{
var drawable = ResourcesCompat.GetDrawable(context.Resources, resourceId, context.Theme);
if (drawable is BitmapDrawable bitmapDrawable)
{
var bitmap = bitmapDrawable.Bitmap;
return new BitmapImage(bitmap);
}
return null;
}
And on iOS:
CGImageImage GetImageStream(string fileName)
{
var iOSimage = UIImage.FromFile(fileName);
var cgImage = new CGImageImage(iOSImage.CGImage, iOSImage.Scale);
return cgImage;
}
BitmapImage and CGImageImage implement IImage in NGraphics.