iOS - 仅将 UIView 的一部分保存为 PNG

Question

我使用以下代码将 UIView 的内容转换为 PNG 图像:

UIGraphicsBeginImageContext(myView.bounds.size);
[myView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

这很好用。如果 UIView 的高度为 500 像素，并且我想生成两张图像(一张是上半部分，一张是下半部分)，我将如何处理做这个？

如有任何帮助，我们将不胜感激。

Answer 1

有几种方法可以做到这一点。一种方法是将其绘制成一张大图，然后制作两张子图:

static UIImage *halfOfImage(UIImage *fullImage, CGFloat yOffset) {
    // Pass yOffset == 0 for the top half.
    // Pass yOffset == 0.5 for the bottom half.

    CGImageRef cgImage = fullImage.CGImage;
    size_t width = CGImageGetWidth(cgImage);
    size_t height = CGImageGetHeight(cgImage);
    CGRect rect = CGRectMake(0, height * yOffset, width, height * 0.5f);

    CGImageRef cgSubImage = CGImageCreateWithImageInRect(cgImage, rect);
    UIImage *subImage = [UIImage imageWithCGImage:cgSubImage scale:fullImage.scale
        orientation:fullImage.imageOrientation];
    CGImageRelease(cgSubImage);
    return subImage;
}

...
    UIGraphicsBeginImageContext(myView.bounds.size);
    [myView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIImage *topHalfImage = halfOfImage(viewImage, 0);
    UIImage *bottomHalfImage = halfOfImage(viewImage, 0.5f);