如何按比例缩放UIImageView？

我有一个UIImageView，目的是通过给它一个高度或宽度来按比例缩小它。

UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://farm4.static.flickr.com/3092/2915896504_a88b69c9de.jpg"]]];
UIImageView *imageView = [[UIImageView alloc] initWithImage:image]; 

//Add image view
[self.view addSubview:imageView];   

//set contentMode to scale aspect to fit
imageView.contentMode = UIViewContentModeScaleAspectFit;

//change width of frame
CGRect frame = imageView.frame;
frame.size.width = 100;
imageView.frame = frame;

图像确实已调整大小，但位置不在左上方。缩放图像/ imageView的最佳方法是什么？如何校正位置？

找到文档后，轻松修复！

 imageView.contentMode = UIViewContentModeScaleAspectFit;

我已经了解了一些关于缩放类型的话题，因此我决定撰写一篇关于一些最流行的内容模式缩放类型的文章。

相关的图像在这里：

我只是试过了，UIImage不支持_imageScaledToSize。

我最终使用类别向UIImage添加了一种方法-我在Apple Dev论坛上发现了一个建议。

在整个项目的.h中-

@interface UIImage (Extras)
- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize;
@end;

实现方式：

@implementation UIImage (Extras)

- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize {

    UIImage *sourceImage = self;
    UIImage *newImage = nil;

    CGSize imageSize = sourceImage.size;
    CGFloat width = imageSize.width;
    CGFloat height = imageSize.height;

    CGFloat targetWidth = targetSize.width;
    CGFloat targetHeight = targetSize.height;

    CGFloat scaleFactor = 0.0;
    CGFloat scaledWidth = targetWidth;
    CGFloat scaledHeight = targetHeight;

    CGPoint thumbnailPoint = CGPointMake(0.0,0.0);

    if (CGSizeEqualToSize(imageSize, targetSize) == NO) {

        CGFloat widthFactor = targetWidth / width;
        CGFloat heightFactor = targetHeight / height;

        if (widthFactor < heightFactor) 
            scaleFactor = widthFactor;
        else
            scaleFactor = heightFactor;

        scaledWidth  = width * scaleFactor;
        scaledHeight = height * scaleFactor;

        // center the image

        if (widthFactor < heightFactor) {
            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5; 
        } else if (widthFactor > heightFactor) {
            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
        }
    }


    // this is actually the interesting part:

    UIGraphicsBeginImageContext(targetSize);

    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = thumbnailPoint;
    thumbnailRect.size.width  = scaledWidth;
    thumbnailRect.size.height = scaledHeight;

    [sourceImage drawInRect:thumbnailRect];

    newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    if(newImage == nil) NSLog(@"could not scale image");


    return newImage ;
}

@end;

imageView.contentMode = UIViewContentModeScaleAspectFill;
imageView.clipsToBounds = YES;

您可以尝试使imageView尺寸匹配image。以下代码未经测试。

CGSize kMaxImageViewSize = {.width = 100, .height = 100};
CGSize imageSize = image.size;
CGFloat aspectRatio = imageSize.width / imageSize.height;
CGRect frame = imageView.frame;
if (kMaxImageViewSize.width / aspectRatio <= kMaxImageViewSize.height) 
{
    frame.size.width = kMaxImageViewSize.width;
    frame.size.height = frame.size.width / aspectRatio;
} 
else 
{
    frame.size.height = kMaxImageViewSize.height;
    frame.size.width = frame.size.height * aspectRatio;
}
imageView.frame = frame;

可以这样调整UIImage的大小

image = [UIImage imageWithCGImage:[image CGImage] scale:2.0 orientation:UIImageOrientationUp];

UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://farm4.static.flickr.com/3092/2915896504_a88b69c9de.jpg"]]];
UIImageView *imageView = [[UIImageView alloc] initWithImage:image]; 


//set contentMode to scale aspect to fit
imageView.contentMode = UIViewContentModeScaleAspectFit;

//change width of frame
//CGRect frame = imageView.frame;
//frame.size.width = 100;
//imageView.frame = frame;

//original lines that deal with frame commented out, yo.
imageView.frame = CGRectMake(10, 20, 60, 60);

...

//Add image view
[myView addSubview:imageView]; 

在顶部发布的原始代码在iOS 4.2中对我来说效果很好。

我发现创建一个CGRect并指定所有的顶部，左侧，宽度和高度值是在我的情况下调整位置的最简单方法，即在表格单元格内使用UIImageView。（仍然需要添加代码以释放对象）

通过选择模式设置为ImageView Aspect Fill并选中该Clip Subviews框。

这对我的Swift 2.x正常工作：

imageView.contentMode = .ScaleAspectFill
imageView.clipsToBounds = true;

UIimageview按比例设置.........

对于Swift：

self.imageViews.contentMode = UIViewContentMode.ScaleToFill

UIImageView + Scale.h：

#import <Foundation/Foundation.h>

@interface UIImageView (Scale)

-(void) scaleAspectFit:(CGFloat) scaleFactor;

@end

UIImageView + Scale.m：

#import "UIImageView+Scale.h"

@implementation UIImageView (Scale)


-(void) scaleAspectFit:(CGFloat) scaleFactor{

    self.contentScaleFactor = scaleFactor;
    self.transform = CGAffineTransformMakeScale(scaleFactor, scaleFactor);

    CGRect newRect = self.frame;
    newRect.origin.x = 0;
    newRect.origin.y = 0;
    self.frame = newRect;
}

@end

我使用以下代码。其中imageCoverView是UIView持有UIImageView

if (image.size.height<self.imageCoverView.bounds.size.height && image.size.width<self.imageCoverView.bounds.size.width)
{
    [self.profileImageView sizeToFit];
    self.profileImageView.contentMode =UIViewContentModeCenter
}
else
{
    self.profileImageView.contentMode =UIViewContentModeScaleAspectFit;
}

如果此处提出的解决方案不适合您，并且您的图像资产实际上是PDF，请注意，XCode实际上将PDF与图像文件区别对待。特别是，它似乎无法缩放以正确填充PDF：它最终以平铺显示。这让我发疯，直到我发现问题出在PDF格式。转换为JPG，您应该一切顺利。

通常，我对我的应用程序使用此方法（与Swift 2.x兼容）：

// Resize UIImage
func resizeImage(image:UIImage, scaleX:CGFloat,scaleY:CGFloat) ->UIImage {
    let size = CGSizeApplyAffineTransform(image.size, CGAffineTransformMakeScale(scaleX, scaleY))
    let hasAlpha = true
    let scale: CGFloat = 0.0 // Automatically use scale factor of main screen

    UIGraphicsBeginImageContextWithOptions(size, !hasAlpha, scale)
    image.drawInRect(CGRect(origin: CGPointZero, size: size))

    let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return scaledImage
}

我想你可以做类似的事情

image.center = [[imageView window] center];

这是您可以轻松扩展的方法。

在Simulator和iPhone中的2.x版本中可以使用。

UIImage *thumbnail = [originalImage _imageScaledToSize:CGSizeMake(40.0, 40.0) interpolationQuality:1];