Question

我从网络资源（> 300MB）下载了大量的UIImage，当我尝试渲染时，由于内存导致应用程序崩溃。我正在尝试使用以下代码调整图像大小：

with cte (StudentId, Fname, LName, DOB, RowCnt)
as (
SELECT StudentId, FirstName, LastName, DateOfBirth as DOB, SUM(1) OVER (Partition By FirstName, LastName, DateOfBirth) as RowCnt
FROM tblStudent
)
SELECT * from CTE where RowCnt > 1
ORDER BY DOB, LName

问题是，正如您可能已经猜到的那样，这需要实际渲染图像，从而导致同样的崩溃。有没有办法在不给系统带来如此巨大的内存压力的情况下调整大图像的大小？

Answer 1

问题在于您将图像保存在内存中。将其下载到磁盘并使用ImageIO框架直接从磁盘读取“缩略图”（较小的大小），而无需将全尺寸图像保存在内存中。

Answer 2

您可以试用+ (UIImage *)decodedImageWithImage:(UIImage *)image maxSize:(NSInteger) maxSize.

中的SDWebImage代码

#define MAX_IMAGE_SIZE 1000
@implementation UIImage (ForceDecode)
+ (CGSize) originalSize:(UIImage*) image
{
    return  CGSizeMake(CGImageGetWidth(image.CGImage), CGImageGetHeight(image.CGImage));
}
+ (UIImage *)decodedImageWithImage:(UIImage *)image {
    return [self decodedImageWithImage:image maxSize:MAX_IMAGE_SIZE];
}
+ (UIImage *)decodedImageWithImage:(UIImage *)image maxSize:(NSInteger) maxSize{
    if (image.images) {
        // Do not decode animated images
        return image;
    }

    CGImageRef imageRef = image.CGImage;
    CGSize imageSize = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));
    imageSize = [self checkMaxImageSize:imageSize maxSize:maxSize];
    CGRect imageRect = (CGRect){.origin = CGPointZero, .size = imageSize};

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);

    int infoMask = (bitmapInfo & kCGBitmapAlphaInfoMask);
    BOOL anyNonAlpha = (infoMask == kCGImageAlphaNone ||
                        infoMask == kCGImageAlphaNoneSkipFirst ||
                        infoMask == kCGImageAlphaNoneSkipLast);

    // CGBitmapContextCreate doesn't support kCGImageAlphaNone with RGB.
    // https://developer.apple.com/library/mac/#qa/qa1037/_index.html
    if (infoMask == kCGImageAlphaNone && CGColorSpaceGetNumberOfComponents(colorSpace) > 1) {
        // Unset the old alpha info.
        bitmapInfo &= ~kCGBitmapAlphaInfoMask;

        // Set noneSkipFirst.
        bitmapInfo |= kCGImageAlphaNoneSkipFirst;
    }
    // Some PNGs tell us they have alpha but only 3 components. Odd.
    else if (!anyNonAlpha && CGColorSpaceGetNumberOfComponents(colorSpace) == 3) {
        // Unset the old alpha info.
        bitmapInfo &= ~kCGBitmapAlphaInfoMask;
        bitmapInfo |= kCGImageAlphaPremultipliedFirst;
    }

    // It calculates the bytes-per-row based on the bitsPerComponent and width arguments.
    CGContextRef context = CGBitmapContextCreate(NULL,
                                                 imageSize.width,
                                                 imageSize.height,
                                                 CGImageGetBitsPerComponent(imageRef),
                                                 0,
                                                 colorSpace,
                                                 bitmapInfo);
    CGColorSpaceRelease(colorSpace);

    // If failed, return undecompressed image
    if (!context) return image;

    CGContextDrawImage(context, imageRect, imageRef);
    CGImageRef decompressedImageRef = CGBitmapContextCreateImage(context);

    CGContextRelease(context);

    UIImage *decompressedImage = [UIImage imageWithCGImage:decompressedImageRef scale:image.scale orientation:image.imageOrientation];
    CGImageRelease(decompressedImageRef);
    return decompressedImage;
}

+ (CGSize) checkMaxImageSize:(CGSize) size maxSize:(NSInteger) max
{
    CGFloat whRatio = size.width / size.height;
    if (size.height > max || size.width > max) {
        if (size.height > size.width) {
            size.width = max * whRatio;
            size.height = max;
        }else{
            size.width = max ;
            size.height = max / whRatio;
        }
    }
    return size;
}

在内存限制下调整UIImage的大小

2 个答案: