Change the state of a customized button (button with an image)?

Question

I know how to change the state of the regular button, as well as change the background color of a regular button. However, when I do UIButton:setBackgroundImage (cu

Answer 1

You need to create a copy of the image in a bitmap context, modify the copy by drawing an overlay or processing it in some way, and then assign the modified image to the button's UIControlStateSelected state.

Here is some sample code that creates the context and draws a 50% black overlay on the image for the selected state of the button, which darkens it:

//assume UIImage* image exists

//get the size of the image
CGFloat pixelsHigh = image.size.height;
CGFloat pixelsWide = image.size.width;

//create a new context the same size as the image
CGContextRef    cx = NULL;
CGColorSpaceRef colorSpace;
void *          bitmapData;
int             bitmapByteCount;
int             bitmapBytesPerRow;

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

colorSpace = CGColorSpaceCreateDeviceRGB();
bitmapData = malloc( bitmapByteCount );
if (bitmapData == NULL)
{
    fprintf (stderr, "Memory not allocated!");
    return;
}
cx = CGBitmapContextCreate (bitmapData,
                                 pixelsWide,
                                 pixelsHigh,
                                 8,      // bits per component
                                 bitmapBytesPerRow,
                                 colorSpace,
                                 kCGImageAlphaPremultipliedLast);
if (cx == NULL)
{
    free (bitmapData);
    fprintf (stderr, "Context not created!");
    return;
}
CGColorSpaceRelease( colorSpace );
CGRect imageRect = CGRectMake(0, 0, pixelsWide, pixelsHigh);

//draw the existing image in the context
CGContextDrawImage(cx, imageRect, image.CGImage);

//draw a 50% black overlay
CGContextSetRGBFillColor(cx, 0, 0, 0, 0.5);
CGContextFillRect(cx, imageRect);

//create a new image from the context
CGImageRef newImage = CGBitmapContextCreateImage(cx);
UIImage* secondaryImage = [UIImage imageWithCGImage:newImage];
CGImageRelease(newImage);
CGContextRelease(cx);

//assign the images to the button
[button setBackgroundImage:image forState:UIControlStateNormal];
[button setBackgroundImage:secondaryImage forState:UIControlStateSelected];