调整UIImage的大小并更改UIImageView的大小

我有这个 UIImageView ，我有它的最大高度和最大宽度的值。我想要实现的是，我想拍摄的图像（任何宽高比和任何分辨率），我想它适合边框，所以图片不超过他们，但它可以收缩他们想要的。 （图片中标记为红色）：

I have this UIImageView and I have the values of its max height and max width. What I want to achieve is that I want to take the image (with any aspect ratio and any resolution) and I want it to fit in the borders, so the picture does not exceed them, but it can shrink them as it wants. (marked red in the picture):

现在图片的大小合适，但我有2个担忧：
1. UIImageView 不等于调整大小的图像的大小，因此留下红色背景（而我不想那样）
2.如果图像小于我的

Right now the image fits the necessary size properly, but I have 2 worries: 1. The UIImageView is not equal the size of the resized image, thus leaving red background (and I don't want that) 2. If the image is smaller that the height of my UIImageView it is not resized to be smaller, it stays the same height.

这是我的代码，我知道它的错误：

Here's my code and I know its wrong:

UIImage *actualImage = [attachmentsArray lastObject];
UIImageView *attachmentImageNew = [[UIImageView alloc] initWithFrame:CGRectMake(5.5, 6.5, 245, 134)];
attachmentImageNew.image = actualImage;
attachmentImageNew.backgroundColor = [UIColor redColor];
attachmentImageNew.contentMode = UIViewContentModeScaleAspectFit;

那么如何动态改变 UIImageView.image ，但是整个 UIImageView ，因此使其大小完全可以调整其内容。

So how do I dynamically change the size not only of the UIImageView.image, but of the whole UIImageView, thus making its size totally adjustable to its content. Any help would be much appreciated, thanks!