Drawing a series of UIImages and memory issues

问题

I need to draw a series of large UIImages on top of each other and I am coming up against memory issues and I was wondering if anybody has a solution.

The code below gives you an example of how my function calls work. The functions have been simplified to show my main issue.

The function "generateImage" has a for loop that calls into a subclass that also returns images that have been generated from a series of paths. I have put @autoreleasepools around the calls so that the images that are generated are immediately deallocated after they are used, but this does not seem to be working and when arrayOfSubImages grows I come up against memory issues.

-( UIImage *)   generateImage
{
    @autoreleasepool {

        UIGraphicsBeginImageContextWithOptions( CGSizeMake( 1000, 1000 ), NO, 0.0 );

        CGContextRef context = UIGraphicsGetCurrentContext();

        UIGraphicsPushContext(context);

        for ( SubImage *subImage in arrayOfSubImages ) {
            UIImage     *aImage = [ subImage imageFromPaths ];
            [ aImage drawAtPoint:CGPointZero ];
        }

        UIGraphicsPopContext();

        UIImage     *image = UIGraphicsGetImageFromCurrentImageContext();

        UIGraphicsEndImageContext();
        return image;
    }
}

The SubImage that is called from generateImage

-( UIImage *)   imageFromPaths
{
    @autoreleasepool {

        UIGraphicsBeginImageContextWithOptions( CGSizeMake( 1000, 1000 ), NO, 0.0 );

        CGContextRef context = UIGraphicsGetCurrentContext();

        UIGraphicsPushContext(context);


        for ( UIBezierPath *path in arrayOfPaths ) {
            [ path fill ];
        }


        UIGraphicsPopContext();

        UIImage     *image = UIGraphicsGetImageFromCurrentImageContext();

        UIGraphicsEndImageContext();
        return image;
    }
}

Any help would be appreciated

Reza

回答1:

I've had similar problems in the past. Try adding an @autoreleasepool within your for-loops because you're likely running into memory problems by performing several memory intensive operations within a tight loop. Memory won't automatically release itself until a loop is over even if that loop is contained in an autoreleasepool -- you need to release each individual iteration.

回答2:

Setting the images to nil directly after using them should release the memory, like so:

-( UIImage *)   generateImage
{
    @autoreleasepool {

    UIGraphicsBeginImageContextWithOptions( CGSizeMake( 1000, 1000 ), NO, 0.0 );

    CGContextRef context = UIGraphicsGetCurrentContext();

    UIGraphicsPushContext(context);

    for ( SubImage *subImage in arrayOfSubImages ) {
        UIImage     *aImage = [ subImage imageFromPaths ];
        [ aImage drawAtPoint:CGPointZero ];
        aImage = nil;
    }

    UIGraphicsPopContext();

    UIImage     *image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
    return image;
}

回答3:

Instead using temp variables, Like:

UIimage * image=

You can define an instance temp variables in you .h file, Like:

UIImage * _image;

Then use it everywhere you define a new image, which needs to be deallocated. It can guarantee you reset memory in time.

Scott is right. I forgot this issue. Release within Loop is the key

来源：https://stackoverflow.com/questions/20304615/drawing-a-series-of-uiimages-and-memory-issues