How to remove or hide the toolbars' top shadow

Question

After removing the background of the toolbar, with an image mask, a shadow line still remains above the toolbar. How do we get rid of it? As you can see, by the image below, I want to use the toolbar and buttons but no background or top shadow.

const float colorMask[6] = {222, 255, 222, 255, 222, 255};
UIImage *_img = [[UIImage alloc] init];
UIImage *_maskedImage = [UIImage imageWithCGImage:CGImageCreateWithMaskingColors(_img.CGImage, colorMask)];
[self.navigationController.toolbar setBackgroundImage:_maskedImage forToolbarPosition:UIToolbarPositionAny barMetrics:UIBarMetricsDefault];

Answer 1

None of the other answers worked on iOS7, some didn't seem to work consistently on older iOS versions either. This (paraphrasing http://samplecodebank.blogspot.com/2013/06/UIToolbar-setShadowImage-forToolbarPosition-example.html) works consistently on 5.1+ for me and is concise and more performant than generating custom background images and color masks.

toolbar.backgroundColor = [UIColor clearColor];
if ([toolbar respondsToSelector:@selector(setBackgroundImage:forToolbarPosition:barMetrics:)]) {
  [toolbar setBackgroundImage:[UIImage new] forToolbarPosition:UIToolbarPositionAny barMetrics:UIBarMetricsDefault];
}
if ([toolbar respondsToSelector:@selector(setShadowImage:forToolbarPosition:)]) {
  [toolbar setShadowImage:[UIImage new] forToolbarPosition:UIToolbarPositionAny];
}

Answer 2

On iOS 7, set [toolBar setClipsToBounds:YES].