iOS超出屏幕的尺寸的图片如何按比例缩放显示

只需加这么一段代码，如下：

imageView.contentMode = UIViewContentModeScaleAspectFit;

imageView.autoresizesSubviews = YES;

imageView.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;