Potential leak of object stored in context

问题:

I am getting a memory leak for this code.

- (CGContextRef) createARGBBitmapContextFromImage:(CGImageRef) imageRef {

    CGContextRef    context = NULL;
    CGColorSpaceRef colorSpace;
    void *          bitmapData;
    int             bitmapByteCount;
    int             bitmapBytesPerRow;

    // Get image width, height. We'll use the entire image.

    size_t pixelsWide = CGImageGetWidth(imageRef);
    size_t pixelsHigh = CGImageGetHeight(imageRef);

    // Declare the number of bytes per row. Each pixel in the bitmap in this
    // example is represented by 4 bytes; 8 bits each of red, green, blue, and
    // alpha.

    bitmapBytesPerRow   = (pixelsWide * 4);
    bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);

    // Use the generic RGB color space.
    colorSpace = CGColorSpaceCreateDeviceRGB();
    if (colorSpace == NULL)
    {
        fprintf(stderr, "Error allocating color space\n");
        return NULL;
    }
    // Allocate memory for image data. This is the destination in memory
    // where any drawing to the bitmap context will be rendered.
    bitmapData = malloc( bitmapByteCount );

    if (bitmapData == NULL)
    {
        fprintf (stderr, "Memory not allocated!");
        CGColorSpaceRelease( colorSpace );
        return NULL;
    }

    // Create the bitmap context. We want pre-multiplied ARGB, 8-bits
    // per component. Regardless of what the source image format is
    // (CMYK, Grayscale, and so on) it will be converted over to the format
    // specified here by CGBitmapContextCreate.

    context = CGBitmapContextCreate (bitmapData,
                                     pixelsWide,
                                     pixelsHigh,
                                     8,      // bits per component
                                     bitmapBytesPerRow,
                                     colorSpace,
                                     kCGImageAlphaPremultipliedFirst);
    if (context == NULL)
    {
        free (bitmapData);
        fprintf (stderr, "Context not created!");
    }

    CGRect rect = {{0,0},{pixelsWide, pixelsHigh}}; 

    //        
    //        // Draw the image to the bitmap context. Once we draw, the memory
    //        // allocated for the context for rendering will then contain the
    //        // raw image data in the specified color space.
    CGContextDrawImage(context, rect, self.CGImage); 

    // Make sure and release colorspace before returning
    CGColorSpaceRelease( colorSpace );

    return context;
}

error: Potential leak of object stored in context.

回答1:

The memory leak analyser uses the name of the method to determine the change in retain count of the returned object. For Obj-C methods it is documented in Basic Memory Management Rules. It states

You create an object using a method whose name begins with “alloc”, “new”, “copy”, or “mutableCopy” (for example, alloc, newObject, or mutableCopy).

The name createARGBBitmapContextFromImage: is not matched by that rule. Instead you should name the method newARGBBitmapContextFromImage:.

Adding the word Create into a function name is used for C functions.