在UIImageView中移動UIImage

Question

我有一個UIImageView （紅色方塊），它將顯示一個必須縮放的UIImage （我可以接收比UIImageView更大或更小的圖像）。 縮放后， UIImage的顯示部分就是它的中心。

我需要的是在藍色方塊中顯示圖像的一部分，我該如何存檔？

我只能獲得圖像大小（高度和寬度），但它顯示原始大小，當它應該是縮放的大小。

self.viewIm = [[UIImageView alloc] initWithFrame:CGRectMake(100, 100, 120, 80)];
self.viewIm.backgroundColor = [UIColor greenColor];
self.viewIm.layer.borderColor = [UIColor redColor].CGColor;
self.viewIm.layer.borderWidth = 5.0;
UIImage *im = [UIImage imageNamed:@"benjen"];
self.viewIm.image = im;
self.viewIm.contentMode = UIViewContentModeScaleAspectFill;
//    self.viewim.clipsToBounds = YES;
[self.view addSubview:self.viewIm];

Answer 1

為了做你想做的事情，我建議你查看CALayer的contentsRect屬性。

既然看到了你的答案，我一直試圖找出適當的解決方案一段時間，但數學逃脫了我因為contentsRect: 'sx和y參數似乎有點神秘......但是這里的一些代碼可能會指向你正確的方向......

float imageAspect = self.imageView.image.size.width/self.imageView.image.size.height;
float imageViewAspect = self.imageView.frame.size.width/self.imageView.frame.size.height;

if (imageAspect > imageViewAspect) {
    float scaledImageWidth = self.imageView.frame.size.height * imageAspect;
    float offsetWidth = -((scaledImageWidth-self.imageView.frame.size.width)/2);
    self.imageView.layer.contentsRect = CGRectMake(offsetWidth/self.imageView.frame.size.width, 0.0, 1.0, 1.0);
} else if (imageAspect < imageViewAspect) {
    float scaledImageHeight = self.imageView.frame.size.width * imageAspect;
    float offsetHeight = ((scaledImageHeight-self.imageView.frame.size.height)/2);
    self.imageView.layer.contentsRect = CGRectMake(0.0, offsetHeight/self.imageView.frame.size.height, 1.0, 1.0);
}

Answer 2

嘗試這樣的事情：

CGRect cropRect = CGRectMake(0,0,200,200);
CGImageRef imageRef = CGImageCreateWithImageInRect([ImageToCrop CGImage],cropRect);
UIImage *image = [UIImage imageWithCGImage:imageRef]; 
CGImageRelease(imageRef);

Answer 3

我發現這個答案非常接近。 其中，類別調整圖像大小，然后使用中心點進行裁剪。 我使用（0,0）作為原點來適應它。 因為我不需要類別，所以我將它用作單一方法。

- (UIImage *)imageByScalingAndCropping:(UIImage *)image forSize:(CGSize)targetSize {
    UIImage *sourceImage = image;
    UIImage *newImage = nil;
    CGFloat scaleFactor = 0.0;
    CGFloat scaledWidth = targetSize.width;
    CGFloat scaledHeight = targetSize.height;

    if (CGSizeEqualToSize(image.size, targetSize) == NO) {
        if ((targetSize.width / image.size.width) > (targetSize.height / image.size.height)) {
            scaleFactor = targetSize.width / image.size.width; // scale to fit height
        } else {
            scaleFactor = targetSize.height / image.size.height; // scale to fit width
        }

        scaledWidth  = image.size.width * scaleFactor;
        scaledHeight = image.size.height * scaleFactor;
    }

    UIGraphicsBeginImageContext(targetSize); // this will crop

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

    [sourceImage drawInRect:thumbnailRect];

    newImage = UIGraphicsGetImageFromCurrentImageContext();

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

    //pop the context to get back to the default
    UIGraphicsEndImageContext();

    return newImage;
}

我的電話是這樣的：

self.viewIm = [[UIImageView alloc] initWithFrame:CGRectMake(100, 100, 120, 80)];
self.viewIm.image = [self imageByScalingAndCropping:[UIImage imageNamed:@"benjen"] forSize:CGSizeMake(120, 80)];
[self.view addSubview:self.viewIm];

Answer 4

我花了一些時間在這上面，最后創建了一個Swift 3.2解決方案（基於我在另一個主題上的一個答案，以及上面的一個答案）。 此代碼僅允許圖像的Y轉換，但通過一些調整，任何人都應該能夠添加水平轉換;）

let yOffset: CGFloat = 20
myImageView.contentMode = .scaleAspectFill

//scale image to fit the imageView's width (maintaining aspect ratio), but allow control over the image's Y position
UIGraphicsBeginImageContextWithOptions(myImageView.frame.size, myImageView.isOpaque, 0.0)
let ratio = myImage.size.width / myImage.size.height
let newHeight = myImageView.frame.width / ratio
let rect = CGRect(x: 0, y: -yOffset, width: myImageView.frame.width, height: newHeight)
myImage.draw(in: rect)
let newImage = UIGraphicsGetImageFromCurrentImageContext() ?? myImage
UIGraphicsEndImageContext()

//set the new image
myImageView.image = newImage

現在，您可以通過更改yOffset來調整圖像所需的向下或向上的yOffset 。