Question

I’m generating UIImages with a bit-bucket, creating them on the fly and swapping the UIImageView’s image. Is there a way to edit the UIImageView’s Image directly? (ie. change the color of a specific pixel, without removing the UIImage from the UIImageView, and get it to redraw.)

Currently, I’m flushing the UIImage and using imageWithCGIImage to make a new one, and assigning it to the UIImageView. This works. Shows no MemLeaks. But on the iPhone (3Gs) after about 100 image replacements, CRASHES. Cache’n issue? The memory summation seems to be hitting the phone’s limit if cache not releasing, however, Simulator does not show memory consumption with each image swap. Stays flatlined without leaks.

Note: topologyImage array is the RGBA pixel-bucket. The REF variables are not released. Every attempt to do so, crashes next call. Without, Instruments reports no leaks.

=========

CGColorSpaceRef colorSpaceRef=CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault | kCGImageAlphaLast;
CGColorRenderingIntent renderingIntent=kCGRenderingIntentDefault;
CGDataProviderRef provider=CGDataProviderCreateWithData(NULL,topologyImage,(I*I*4),NULL);
CGImageRef imageRef=CGImageCreate(I,I,8,4*8,4*I,colorSpaceRef,bitmapInfo,provider,NULL,false,renderingIntent);

UIImage *img=[UIImage imageWithCGImage:imageRef];
if( IMG[NDXtopo].vw ) {
    [IMG[NDXtopo].vw setImage:img];
    }
else {
    IMG[NDXtopo].vw=[[UIImageView alloc] initWithImage:img];
    [master.view addSubview:IMG[NDXtopo].vw];
    }

Answer 1

Basically you should release your references, especially the CGImageRef since the imageWithCGImage doesn’t take ownership of the CGImage but rather seems to copy the data internally.

The docs on this are quite unclear, but from what I have found in my testing if I don’t release CGImageRefs and CGDataProviderRefs it will eventually cause the application to get memory warnings… and then crash.

Not sure why you would have a crash, but in doing a quick test with:

UIImageView *view = [[UIImageView alloc] init];
int I = 128;
unsigned char *topologyImage = malloc(I*I*4*sizeof(unsigned char));

for(int i=0; i<I*I*4; i++)
{
  topologyImage[i] = 100;
}

for(int i=0; i<1000; i++)
{
    CGColorSpaceRef colorSpaceRef=CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault | kCGImageAlphaLast;
    CGColorRenderingIntent renderingIntent=kCGRenderingIntentDefault;
    CGDataProviderRef provider=CGDataProviderCreateWithData(NULL,topologyImage,(I*I*4),NULL);
    CGImageRef imageRef=CGImageCreate(I,I,8,4*8,4*I,colorSpaceRef,bitmapInfo,provider,NULL,false,renderingIntent);
    CGColorSpaceRelease(colorSpaceRef);
    CGDataProviderRelease(provider);

    UIImage *img=[UIImage imageWithCGImage:imageRef];
    view.image = img;
    CGImageRelease(imageRef);
}
free(topologyimage);

Seems to work just fine for me, so whatever is causing your crash seems to be because of something outside of your example, like for example how you got the image data into the topologyImage