iOS上的CGImage旋转方法内存泄漏

Question

我有这个代码来旋转CGImage：

- (CGImageRef)rotateCGImageRef:(CGImageRef)imageRef toOrientation:(UIImageOrientation)orientation
{
    CGRect             bnds = CGRectZero;
    CGImageRef         copy = nil;
    CGContextRef       ctxt = nil;
    CGRect             rect = CGRectZero;
    CGAffineTransform  tran = CGAffineTransformIdentity;

    @autoreleasepool {
        bnds.size = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef)); //self.size;
        rect.size = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef)); //self.size;

        switch (orientation)
        {
            case UIImageOrientationUp:
                return imageRef;

            case UIImageOrientationUpMirrored:
                tran = CGAffineTransformMakeTranslation(rect.size.width, 0.0);
                tran = CGAffineTransformScale(tran, -1.0, 1.0);
                break;

            case UIImageOrientationDown:
                tran = CGAffineTransformMakeTranslation(rect.size.width, rect.size.height);
                tran = CGAffineTransformRotate(tran, degreesToRadians(180.0));
                break;

            case UIImageOrientationDownMirrored:
                tran = CGAffineTransformMakeTranslation(0.0, rect.size.height);
                tran = CGAffineTransformScale(tran, 1.0, -1.0);
                break;

            case UIImageOrientationLeft:
                bnds.size = swapWidthAndHeight(bnds.size);
                tran = CGAffineTransformMakeTranslation(0.0, rect.size.width);
                tran = CGAffineTransformRotate(tran, degreesToRadians(-90.0));
                break;

            case UIImageOrientationLeftMirrored:
                bnds.size = swapWidthAndHeight(bnds.size);
                tran = CGAffineTransformMakeTranslation(rect.size.height, rect.size.width);
                tran = CGAffineTransformScale(tran, -1.0, 1.0);
                tran = CGAffineTransformRotate(tran, degreesToRadians(-90.0));
                break;

            case UIImageOrientationRight:
                bnds.size = swapWidthAndHeight(bnds.size);
                tran = CGAffineTransformMakeTranslation(rect.size.height, 0.0);
                tran = CGAffineTransformRotate(tran, degreesToRadians(90.0));
                break;

            case UIImageOrientationRightMirrored:
                bnds.size = swapWidthAndHeight(bnds.size);
                tran = CGAffineTransformMakeScale(-1.0, 1.0);
                tran = CGAffineTransformRotate(tran, degreesToRadians(90.0));
                break;

            default:
                // orientation value supplied is invalid
                assert(false);
                return nil;
        }

        UIGraphicsBeginImageContext(bnds.size);
        ctxt = UIGraphicsGetCurrentContext();

        switch (orientation)
        {
            case UIImageOrientationLeft:
            case UIImageOrientationLeftMirrored:
            case UIImageOrientationRight:
            case UIImageOrientationRightMirrored:
                CGContextScaleCTM(ctxt, -1.0, 1.0);
                CGContextTranslateCTM(ctxt, -rect.size.height, 0.0);
                break;

            default:
                CGContextScaleCTM(ctxt, 1.0, -1.0);
                CGContextTranslateCTM(ctxt, 0.0, -rect.size.height);
                break;
        }

        CGContextConcatCTM(ctxt, tran);
        CGContextDrawImage(ctxt, rect, imageRef);

        //copy = UIGraphicsGetImageFromCurrentImageContext();
        copy = CGBitmapContextCreateImage(ctxt);
        UIGraphicsEndImageContext();
    }
    return copy;
}

但 Analyzer 说它有泄漏：

我无法释放复制对象，因为我的方法正在返回它。

实际上泄漏了什么？

编辑： 这是转换为 C 函数的最终代码：

CGImageRef CreateRotatedImage(CGImageRef imageRef, UIImageOrientation orientation)
{
    CGRect             bnds = CGRectZero;
    CGImageRef         copy = nil;
    CGContextRef       ctxt = nil;
    CGRect             rect = CGRectZero;
    CGAffineTransform  tran = CGAffineTransformIdentity;

    bnds.size = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef)); //self.size;
    rect.size = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef)); //self.size;

    switch (orientation)
    {
        case UIImageOrientationUp:
            return imageRef;

        case UIImageOrientationUpMirrored:
            tran = CGAffineTransformMakeTranslation(rect.size.width, 0.0);
            tran = CGAffineTransformScale(tran, -1.0, 1.0);
            break;

        case UIImageOrientationDown:
            tran = CGAffineTransformMakeTranslation(rect.size.width, rect.size.height);
            tran = CGAffineTransformRotate(tran, degreesToRadians(180.0));
            break;

        case UIImageOrientationDownMirrored:
            tran = CGAffineTransformMakeTranslation(0.0, rect.size.height);
            tran = CGAffineTransformScale(tran, 1.0, -1.0);
            break;

        case UIImageOrientationLeft:
            bnds.size = swapWidthAndHeight(bnds.size);
            tran = CGAffineTransformMakeTranslation(0.0, rect.size.width);
            tran = CGAffineTransformRotate(tran, degreesToRadians(-90.0));
            break;

        case UIImageOrientationLeftMirrored:
            bnds.size = swapWidthAndHeight(bnds.size);
            tran = CGAffineTransformMakeTranslation(rect.size.height, rect.size.width);
            tran = CGAffineTransformScale(tran, -1.0, 1.0);
            tran = CGAffineTransformRotate(tran, degreesToRadians(-90.0));
            break;

        case UIImageOrientationRight:
            bnds.size = swapWidthAndHeight(bnds.size);
            tran = CGAffineTransformMakeTranslation(rect.size.height, 0.0);
            tran = CGAffineTransformRotate(tran, degreesToRadians(90.0));
            break;

        case UIImageOrientationRightMirrored:
            bnds.size = swapWidthAndHeight(bnds.size);
            tran = CGAffineTransformMakeScale(-1.0, 1.0);
            tran = CGAffineTransformRotate(tran, degreesToRadians(90.0));
            break;

        default:
            // orientation value supplied is invalid
            assert(false);
            return nil;
    }

    UIGraphicsBeginImageContext(bnds.size);
    ctxt = UIGraphicsGetCurrentContext();

    switch (orientation)
    {
        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
            CGContextScaleCTM(ctxt, -1.0, 1.0);
            CGContextTranslateCTM(ctxt, -rect.size.height, 0.0);
            break;

        default:
            CGContextScaleCTM(ctxt, 1.0, -1.0);
            CGContextTranslateCTM(ctxt, 0.0, -rect.size.height);
            break;
    }

    CGContextConcatCTM(ctxt, tran);
    CGContextDrawImage(ctxt, rect, imageRef);

    //copy = UIGraphicsGetImageFromCurrentImageContext();
    copy = CGBitmapContextCreateImage(ctxt);
    UIGraphicsEndImageContext();
    return copy;
}

调用这个 C 函数：

imageRef = CreateRotatedImage(imageRef, UIImageOrientationRight);

Answer 1

我认为您的问题是您从 Obj-C 方法返回 CGImageRef。 CGImageRef 是 C-struct 指针的 typedef，而不是 NSObject，因此它不能自动释放。

我会考虑两种选择 - 将方法转换为 C 函数或将返回值放入 NSObject（例如 UIImage）。

编辑：

CGImageRef CreateRotatedImage(CGImageRef imageRef, UIImageOrientation toOrientation) {
    [... your code ...]
}

呼叫：

CGImageRef rotatedImage = CreateRotatedImage(image, orientation);

Answer 2

你必须释放你的CGImageRef copy。 CFType 应该知道如何处理release 和autorelease。试试这个：

return (CGImageRef)[(id)copy autorelease];

首先，您必须将其转换为 Objective-C 指针。随后，您将其转换回 CGImageRef。看到这个答案：https://*.com/a/7061168/656036

Answer 3

您应该阅读分析仪所说的内容：这是一个潜在泄漏。 Analyzer 不会告诉您这是否真的是泄漏，以获取从仪器运行泄漏工具所需的信息。

分析器正确地警告您返回一个您必须自己释放的值。

在你的接收函数中，调用

CGImageRelease(img);

在你完成CGImageRef之后。