CODEWITHSUNDEEP
iosobjective-cmemoryuiimageautomatic-ref-counting
Jack Huang
Jack Huang

Reputation: 41

Why the UIImage is not released by ARC when I used UIGraphicsGetImageFromCurrentImageContext inside of a block

I try to download an image from server by using the NSURLSessionDownloadTask(iOS 7 API), and inside of the completion block, I want to the original image to be resized and store locally. So I wrote the helper method to create the bitmap context and draw the image, then get the new image from UIGraphicsGetImageFromCurrentImageContext(). The problem is the image is never released every time I do this. However, if I don't use the context and image drawing, things just work fine and no memory increasing issue. There is no CGImageCreate/Release function called, so really nothing to manually release here, and nothing fixed by adding @autoreleasepool here. Is there any way to fix this? I really want to modify the original image after downloading and before storing.

Here is some snippets for the issue:

[self fetchImageByDownloadTaskWithURL:url completion:^(UIImage *image, NSError *error) {

    UIImage *modifiedImage = [image resizedImageScaleAspectFitToSize:imageView.frame.size];

    // save to local disk
    // ...
}];

// This is the resize method in UIImage Category
- (UIImage *)resizedImageScaleAspectFitToSize:(CGSize)size
{
    CGSize imageSize = [self scaledSizeForAspectFitToSize:size];

    UIGraphicsBeginImageContextWithOptions(imageSize, YES, 0.0);
    CGRect imageRect = CGRectMake(0.0, 0.0, imageSize.width, imageSize.height);
    [self drawInRect:imageRect]; // nothing will change if make it weakSelf
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;
}

updates:

When I dig into with allocations instrument, I find out that the memory growth is related with "VM: CG raster data". In my storing method, I use the NSCache for a photo memory cache option before store it persistently, and the raster data eats a lot of memory if I use the memory cache. It seems like after the rendered image being cached, all drawing data is also alive in memory until I release all cached images. If I don't memory cache the image, then non of raster data that coming from my image category method will be alive in memory. I just can not figure out why the drawing data is not released after image is being cached? Shouldn't it being released after drawing?

new updates:

I still didn't figure out why raster data is not being released when image for drawing is alive, and there is no analyze warning about this for sure. So I guess I just have to not cache the huge image for drawing to fit the big size, and remove cached drawing images when I don't want to use them any more. If I call [UIImage imageNamed:] and make it drawing, it seems never being released with raster data together since the image is system cached. So I called [UIImage imageWithContentsOfFile:] instead. Eventually the memory performs well. Other memory growth are something called non-object in allocations instrument which I have no idea currently. The memory warning simulation will release the system cached image created by [UIImage imageNamed:]. But for raster data, I will give some more tests on tomorrow and see.

Upvotes: 0

Views: 555

Answers (1)

Avi
Avi

Reputation: 7552

Try making your category method a class method instead. Perhaps the leak is the original CGImage data which you are overwriting when you call [self drawInRect:imageRect];.

Upvotes: 0

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