How to move image in the background of the view? [duplicate] - iphone

Question

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Closed 10 years ago.
I have a problem in my application i have a moving image it works fine.
But my image is also moving over a button, that i can't click when the image is before the button. How can i make sure that the image is moving on the background of my view so i can still press the button.
This is the code for the moving image
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
[[self navigationController] setNavigationBarHidden:YES animated:YES];
[self loadImage];
image = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"cow.png"]];
image.frame =self.view.bounds;
[[self view] addSubview:image];
[NSTimer scheduledTimerWithTimeInterval: 3
target: self
selector:#selector(moveImage:)
userInfo: nil repeats:YES];
}
-(void) moveImage: (NSTimer*)timer {
CGFloat x = (CGFloat) (arc4random() % (int) self.view.bounds.size.width);
CGFloat y = (CGFloat) (arc4random() % (int) self.view.bounds.size.height);
CGPoint pointOne=CGPointMake(x,y);
image.center=pointOne;
}
}

Answer 1

The problem lies in the fact that arc4random_uniform() calls take an upper bounds, not a 0-based count of args (as you, cleverly some would say, extrapolated). Your equation is nearly-sound, however flawed in a few places, which I've tried to correct with some documentation:
-(void)someAction:(id)sender {
NSInteger imageIndex1 = arc4random_uniform(self.images.count); //upper bounds, so no -1
NSInteger imageIndex2 = arc4random_uniform(self.images.count); //upper bounds, so no -1
NSInteger imageIndex3 = arc4random_uniform(self.images.count); //upper bounds, so no -1
_Bool b1 = true, b2 = true, b3 = true; //I can only assume you've been declaring GNU C booleans because of the lowercase false.
//be careful, in Objective-C land, BOOL is signed char.
if (imageIndex1 == imageIndex2) {
b1 = false;
imageIndex2 = arc4random_uniform(self.images.count); //upper bounds, so no -1
}
if(imageIndex1 == imageIndex3) {
b2 = false;
imageIndex1 = arc4random_uniform(self.images.count); //upper bounds, so no -1
}
if (imageIndex2 == imageIndex3) {
b3 = false;
imageIndex3 = arc4random_uniform(self.images.count); //upper bounds, so no -1
}
//You have to use ors here, otherwise your UI will never actually update, considering that in checking
//for unique factors, then reassigning to another unique factor if a check fails, one of them has got
//to be true before the UI can update, rather than all 3 at once.
//Perhaps an individual check of each boolean would be more effective.
if(b1 == true || b2 == true || b3 == true ) {
[self.picture1 setImage:self.images[imageIndex1]];
[self.picture2 setImage:self.images[imageIndex2]];
[self.picture3 setImage:self.images[imageIndex3]];
}
}

Answer 2

I'm guessing you're looking for a random index that isn't the current index, so that you can pick a random, different index, rather than just a random index.
- (NSUInteger)randomUnsignedLessThan:(NSInteger)max excluding:(NSUInteger)exclude {
NSInteger firstTry = -1;
while (firstTry == exclude) firstTry = arc4random() % max;
return firstTry;
}
Note that this approach will always call arc4random once, and require 1+N calls with a probability of 1/max^N, so for low ranges, and high performance requirements, you might consider a different algorithm to exclude the one index.