使用Aspect Fit对齐UIImageView

Question

对于我的UIImageView，我选择了Aspect Fit (InterfaceBuilder)，但我如何更改垂直对齐方式？

Answer 1

编辑-这段代码有点发霉，来自2011年，除了我合并了@ArtOfWarefare的mods

你不能用/ UIImageView来做这件事。我创建了一个包含UIImageView的简单UIView子类MyImageView。下面的代码。

// MyImageView.h
#import <UIKit/UIKit.h>

@interface MyImageView : UIView {
    UIImageView *_imageView;
}

@property (nonatomic, assign) UIImage *image;

@end

和

// MyImageView.m

#import "MyImageView.h"

@implementation MyImageView

@dynamic image;

- (id)initWithCoder:(NSCoder*)coder
{
    self = [super initWithCoder:coder];
    if (self) {
        self.clipsToBounds = YES;
        _imageView = [[UIImageView alloc] initWithFrame:self.bounds];
        _imageView.contentMode = UIViewContentModeScaleAspectFill;
        [self addSubview:_imageView];
    }
    return self;
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.clipsToBounds = YES;
        _imageView = [[UIImageView alloc] initWithFrame:self.bounds];
        _imageView.contentMode = UIViewContentModeScaleAspectFill;
        [self addSubview:_imageView];
    }
    return self;
}

- (id)initWithImage:(UIImage *)anImage
{
    self = [self initWithFrame:CGRectZero];
    if (self) {
        _imageView.image = anImage;
        [_imageView sizeToFit];

        // initialize frame to be same size as imageView
        self.frame = _imageView.bounds;        
    }
    return self;
}

// Delete this function if you're using ARC
- (void)dealloc
{
    [_imageView release];
    [super dealloc];
}

- (UIImage *)image
{
    return _imageView.image;
}

- (void)setImage:(UIImage *)anImage
{
    _imageView.image = anImage;
    [self setNeedsLayout];
}

- (void)layoutSubviews
{
    if (!self.image) return;

    // compute scale factor for imageView
    CGFloat widthScaleFactor = CGRectGetWidth(self.bounds) / self.image.size.width;
    CGFloat heightScaleFactor = CGRectGetHeight(self.bounds) / self.image.size.height;

    CGFloat imageViewXOrigin = 0;
    CGFloat imageViewYOrigin = 0;
    CGFloat imageViewWidth;
    CGFloat imageViewHeight;


    // if image is narrow and tall, scale to width and align vertically to the top
    if (widthScaleFactor > heightScaleFactor) {
        imageViewWidth = self.image.size.width * widthScaleFactor;
        imageViewHeight = self.image.size.height * widthScaleFactor;
    }

    // else if image is wide and short, scale to height and align horizontally centered
    else {
        imageViewWidth = self.image.size.width * heightScaleFactor;
        imageViewHeight = self.image.size.height * heightScaleFactor;
        imageViewXOrigin = - (imageViewWidth - CGRectGetWidth(self.bounds))/2;
    }

    _imageView.frame = CGRectMake(imageViewXOrigin,
                                  imageViewYOrigin,
                                  imageViewWidth,
                                  imageViewHeight);
}

- (void)setFrame:(CGRect)frame
{
    [super setFrame:frame];
    [self setNeedsLayout];
}

@end

Answer 2

如果使用故事板，这可以在有约束的情况下实现。

首先，具有所需的最终帧/约束的UIView。向UIView添加UIImageView。将contentMode设置为Aspect Fill。使UIImageView帧与图像的比例相同(这样可避免以后出现任何故事板警告)。使用标准约束将边固定到UIView。使用标准约束将顶部或底部(取决于您希望其对齐的位置)固定到UIView。最后，向UIImageView添加一个纵横比约束(确保ratio作为图像)。

Answer 3

这有点棘手，因为如果您已经选择了一个内容模式(.scaleAspectFit)，则没有选项来设置进一步的对齐规则。

但这里有一个解决方法：

首先需要通过计算尺寸来显式地调整源图像的大小(如果它在带有contentMode = .scaleAspectFit的UIImageView中)。

extension UIImage {

    func aspectFitImage(inRect rect: CGRect) -> UIImage? {
        let width = self.size.width
        let height = self.size.height
        let aspectWidth = rect.width / width
        let aspectHeight = rect.height / height
        let scaleFactor = aspectWidth > aspectHeight ? rect.size.height / height : rect.size.width / width

        UIGraphicsBeginImageContextWithOptions(CGSize(width: width * scaleFactor, height: height * scaleFactor), false, 0.0)
        self.draw(in: CGRect(x: 0.0, y: 0.0, width: width * scaleFactor, height: height * scaleFactor))

        defer {
            UIGraphicsEndImageContext()
        }

        return UIGraphicsGetImageFromCurrentImageContext()
    }
}

然后，您只需通过传递imageView的帧来对原始图像调用此函数，并将结果赋给UIImageView.image属性。此外，请确保在此处(甚至在界面生成器中)设置imageView所需的contentMode！

let image = UIImage(named: "MySourceImage")
imageView.image = image?.aspectFitImage(inRect: imageView.frame)
imageView.contentMode = .left