如何根据设备大小和比例调整 UIImage 的大小？

Question

我有一个大小为 (1008, 669) 的 UIImage 如何根据我的设备大小调整它的大小（例如，如果我在 iPhone4s 中查看它，它的宽度将为 640 x 960 ((320 *retina_scale) x (480) *retina_scale))）。我使用下面的方法来做到这一点，但我的图像只是在UIImageView拉伸。如何处理这个？如何使其动态，以便它可以工作所有类型的图像？

- (UIImage *) hResizeImage:(UIImage *)image withTargetSize:(CGSize)targetSize {
    CGSize size = image.size;
    CGFloat widthRatio = targetSize.width / image.size.width;
    CGFloat heightRatio = targetSize.height / image.size.height;

    // Figure out what our orientation is, and use that to form the rectangle
    CGSize newSize;
    if(widthRatio > heightRatio) {
        newSize = CGSizeMake(size.width * heightRatio, size.height * heightRatio);
    } else {
        newSize = CGSizeMake(size.width * widthRatio,  size.height * widthRatio);
    }

    // This is the rect that we've calculated out and this is what is actually used below
    CGRect scaledRect = CGRectMake(0, 0, newSize.width * [UIScreen mainScreen].scale, newSize.height * [UIScreen mainScreen].scale);

    // Actually do the resizing to the rect using the ImageContext stuff
    UIGraphicsBeginImageContextWithOptions(scaledRect.size, false, [UIScreen mainScreen].scale);
    [image drawInRect:scaledRect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

Answer 1

由于在 UIGraphicsBeginImageContextWithOptions 中指定了比例因子，因此在计算 scaledRect 时不需要将宽高乘以屏幕比例。

并且如果在 UIGraphicsBeginImageContextWithOptions 中指定了 0.0 的值，则比例因子会自动设置为设备主屏幕的比例因子。

- (UIImage *)hResizeImage:(UIImage *)image withTargetSize:(CGSize)targetSize {
    CGSize size = image.size;
    CGFloat widthRatio = targetSize.width / image.size.width;
    CGFloat heightRatio = targetSize.height / image.size.height;

    // Figure out what our orientation is, and use that to form the rectangle
    CGSize newSize;
    if(widthRatio > heightRatio) {
        newSize = CGSizeMake(size.width * heightRatio, size.height * heightRatio);
    } else {
        newSize = CGSizeMake(size.width * widthRatio,  size.height * widthRatio);
    }

    // This is the rect that we've calculated out and this is what is actually used below
    CGRect scaledRect = CGRectMake(0, 0, newSize.width, newSize.height);

    // Actually do the resizing to the rect using the ImageContext stuff
    UIGraphicsBeginImageContextWithOptions(scaledRect.size, false, 0.0f);
    [image drawInRect:scaledRect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}