iphone - Focus effect (just like UIAlertView)

Question

I know title of my question is so bad, but I don't know how to describe it.

When an UIAlertView pops up, anything else on the screen (except the UIAlertView) becomes a bit darker but can be seen. I call this as Focus effect, because you will know clearly and directly that now the UIAlertView is the focus.

So how can I implement such a focus effect?

thanks

Answer 1

Just add a translucent view below the view you want to "focus" on. Simple example:

UIView *shieldView = [[[UIView alloc] initWithFrame:myView.bounds] autorelease];
shieldView.backgroundColor = [UIColor colorWithWhite:0.0 alpha:0.7];
[myView.superview insertSubview:shieldView belowSubview:myView];

UIAlertView actually uses an image with a radial gradient instead of a simple color, in order to highlight the center of the view.

Answer 2

I know this post is a bit old but I thought it might help someone.

Use this code to generate the radial gradient background:

- (UIImage *)radialGradientImage:(CGSize)size start:(float)start end:(float)end centre:(CGPoint)centre radius:(float)radius{
UIGraphicsBeginImageContextWithOptions(size, YES, 1);

size_t count = 2;
CGFloat locations[2] = {0.0, 1.0};
CGFloat components[8] = {start, start, start, 1.0, end, end, end, 1.0};

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGGradientRef grad = CGGradientCreateWithColorComponents (colorSpace, components, locations, count);
CGColorSpaceRelease(colorSpace);

CGContextDrawRadialGradient (UIGraphicsGetCurrentContext(), grad, centre, 0, centre, radius, kCGGradientDrawsAfterEndLocation);

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

CGGradientRelease(grad);
UIGraphicsEndImageContext();
return image;}

Define gradient in the .h file like so:

UIImageView *gradient;

Call your gradient like so:

- (void)addGradient{
CGSize size = self.view.bounds.size;
CGPoint centre = CGPointMake(self.view.bounds.size.width/2, self.view.bounds.size.height/2);

float startColor = 1.0f; 
float endColor = 0.0f;
float radius = MIN(self.view.bounds.size.width/4, self.view.bounds.size.height/4); 

gradient = [[UIImageView alloc] initWithImage:[self radialGradientImage:size 
                                                                  start:startColor 
                                                                    end:endColor 
                                                                 centre:centre 
                                                                 radius:radius]];

[gradient setBackgroundColor:[UIColor clearColor]];
[gradient setUserInteractionEnabled:YES];
[gradient setAlpha:0.6f];
[self.view addSubview:gradient];}