如何使用固定宽度和自动布局正确缩放图像？

Question

我有一个动态UIImage和UIImageView,固定宽度为280.0px,我正在使用自动布局.在UIImage视图中,我设置了宽度和高度约束,并降低了高度约束的优先级.我选择了"方面适合",并将内容拥抱和压缩优先级提高到1000.在这种情况下,调整UIImageView以保持比率,但高度比我想要的更大.保留宽高比,因为UIImageView的顶部和底部有空白空间.我想删除这些空格并自动调整高度以完全适合UIImage.

Answer 1

像这样......

UIImage *image = ...;
UIImageView *imageView = ...;

imageView.image = image;
float ar = image.size.width/image.size.height;

NSLayoutConstraint* aspectConstraint = [NSLayoutConstraint constraintWithItem: imageView
                                                         attribute: NSLayoutAttributeWidth
                                                         relatedBy: NSLayoutRelationEqual
                                                            toItem: imageView
                                                         attribute: NSLayoutAttributeHeight
                                                        multiplier: ar
                                                          constant: 0];

[parentView addConstraint: aspectConstraint];

Answer 2

我已经解决如下：

-(CGFloat) scaleImageAutoLayout:(UIImageView *)imageView withWidth:(CGFloat)width
{
    CGFloat scale = width/imageView.image.size.width;
    CGFloat height = imageView.image.size.height * scale;
    NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings(imageView);
    [imageView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:[NSString     stringWithFormat:@"V:[imageView(%f)]",ceilf(height)]
                                                                  options:0 metrics:nil    views:viewsDictionary]];
    return height;
}