これを正しく行うには、実際にプログラムで画像のサイズを変更して操作し、目的のアスペクト比を取得します。これにより、ビュー階層をハッキングする必要がなくなり、すべての再描画ではなく、単一の操作に対するパフォーマンスの低下も軽減されます。
この(テストされていない)コードは、私が何を意味するかを説明するのに役立つはずです。
CGSize imageSize = image.size;
CGFloat currentAspect = imageSize.width / imageSize.height;
// for purposes of illustration
CGFloat targetWidth = 100;
CGFloat targetHeight = 100;
CGFloat targetAspect = targetWidth / targetHeight;
CGFloat newWidth, newHeight;
if (currentAspect > targetAspect) {
// width will end up at 100, height needs to be smaller
newWidth = targetWidth;
newHeight = targetWidth / currentAspect;
} else {
// height will end up at 100, width needs to be smaller
newHeight = targetHeight;
newWidth = targetHeight * currentAspect;
}
size_t bytesPerPixel = 4;
// although the image will be resized to { newWidth, newHeight }, it needs
// to be padded with empty space to provide the aspect fit behavior
//
// use calloc() to clear the data as it's allocated
void *imageData = calloc(targetWidth * targetHeight, bytesPerPixel);
if (!imageData) {
// error out
return;
}
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
if (!colorSpace) {
// error out
return;
}
CGContextRef context = CGBitmapContextCreate(
imageData,
targetWidth,
targetHeight,
8, // bits per component
targetWidth * bytesPerPixel, // bytes per row
colorSpace,
kCGBitmapByteOrder32Host | kCGImageAlphaPremultipliedFirst
);
CGColorSpaceRelease(colorSpace);
// now we have a context to draw the original image into
// in doing so, we want to center it, so prepare the geometry
CGRect drawRect = CGRectMake(
floor((targetWidth - newWidth) / 2),
floor((targetHeight - newHeight) / 2),
round(newWidth),
round(newHeight)
);
CGContextDrawImage(context, drawRect, image.CGImage);
// now that the bitmap context contains the aspect fit image with transparency
// letterboxing, we want to pull out a new image from it
CGImageRef newImage = CGBitmapContextCreateImage(context);
// destroy the temporary context
CGContextRelease(context);
free(imageData);
// and, finally, create a new UIImage
UIImage *newUIImage = [UIImage imageWithCGImage:newImage];
CGImageRelease(newImage);
その一部が不明な場合はお知らせください。