public static class ImageHelper
{
public static UIImage Scale (UIImage source, SizeF newSize)
{
UIGraphics.BeginImageContext (newSize);
var context = UIGraphics.GetCurrentContext ();
context.InterpolationQuality=CGInterpolationQuality.High;
context.TranslateCTM (0, newSize.Height);
context.ScaleCTM (1f, -1f);
context.DrawImage (new RectangleF (0, 0, newSize.Width, newSize.Height), source.CGImage);
var scaledImage = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
return scaledImage;
}
public static UIImage Rotate (UIImage image)
{
UIImage res;
using (CGImage imageRef = image.CGImage) {
CGImageAlphaInfo alphaInfo = imageRef.AlphaInfo;
CGColorSpace colorSpaceInfo = CGColorSpace.CreateDeviceRGB ();
if (alphaInfo == CGImageAlphaInfo.None) {
alphaInfo = CGImageAlphaInfo.NoneSkipLast;
}
int width, height;
width = imageRef.Width;
height = imageRef.Height;
int maxSize = Math.Max (width, height);
if (height >= width) {
width = (int)Math.Floor ((double)width * ((double)maxSize / (double)height));
height = maxSize;
} else {
height = (int)Math.Floor ((double)height * ((double)maxSize / (double)width));
width = maxSize;
}
CGBitmapContext bitmap;
if (image.Orientation == UIImageOrientation.Up || image.Orientation == UIImageOrientation.Down) {
bitmap = new CGBitmapContext (IntPtr.Zero, width, height, imageRef.BitsPerComponent, imageRef.BytesPerRow, colorSpaceInfo, alphaInfo);
} else {
bitmap = new CGBitmapContext (IntPtr.Zero, height, width, imageRef.BitsPerComponent, imageRef.BytesPerRow, colorSpaceInfo, alphaInfo);
}
switch (image.Orientation) {
case UIImageOrientation.Left:
bitmap.RotateCTM ((float)Math.PI / 2);
bitmap.TranslateCTM (0, -height);
break;
case UIImageOrientation.Right:
bitmap.RotateCTM (-((float)Math.PI / 2));
bitmap.TranslateCTM (-width, 0);
break;
case UIImageOrientation.Up:
break;
case UIImageOrientation.Down:
bitmap.TranslateCTM (width, height);
bitmap.RotateCTM (-(float)Math.PI);
break;
}
bitmap.DrawImage (new Rectangle (0, 0, width, height), imageRef);
res = UIImage.FromImage (bitmap.ToImage ());
bitmap = null;
}
return res;
}
}
调用方法=> UIImage ScaledImage =ImageHelper.Scale (ImageHelper.Rotate (downloadedImage), new SizeF (270, 260));
请提供任何解决方案以保持质量，并将其扩展到所需的大小。