How can I make a UILabel change positions randomly? - ios

Question

What I mean by this is, if I have a UILabel that I created, how can I make it change periodically within the view of the screen to a random point? Would I use something like arc4random, or something like a random CGPointMake?
I would have it change every second or so using something like this
Text = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(RandomText) userInfo:nil repeats:YES] ;
but i'm just not sure how to get it to "spawn" in a random place, if possible, and then to remove the other one.
A simpler version would also be, If I just made say, 4 different UILabels, how could I make it appear randomly on one of the 4, and then remove after the time interval? I assume I could use something like
int randomNumber = rand() % 4;
and then put a switch in there, but i'm not sure if that would be the correct way to do it either.

Answer 1

Do you have a single label that you want to move to different points on the screen? Or are you adding multiple labels?
Are you using auto-layout or not? (If you're using auto-layout then you can't just move the label around - instead you need to modify it's position constraints. That gets a little more complicated.)
As to how to move it around, I would suggest using arc4random_uniform to calculate a new location for the label's center.
You could put code like the following into your timer method. In the code below, "view" is the view that contains your label.
The code below keeps the label fully visible on-screen by moving the center no closer to the edges of it's parent view than half the label's width&height.
CGFloat newX = arc4random_uniform(view.bounds.width - label.bounds.width) +
label.bounds.width/2;
CGFloat newY = arc4random_uniform(view.bounds.height - label.bounds.height) + label.bounds.height/2;
label.center = CGPointMake(newX, newY);
If you want the label to move to it's new location in an animation you could use the UIView method animateWithDuration:animations to change the center point in an animation block.
Again, if you're using AutoLayout, you'll need to attach center X and center Y constraints as outlets, and change their value settings to move the label.

Answer 2

Interesting. Maybe this helps. This is just a prototype; by no way a production code. Hope this helps. Consider label,screenHeight and screenWidth as instance level variables.
- (void)viewDidLoad
{
[super viewDidLoad];
label = [[UILabel alloc]initWithFrame:CGRectMake(0, 0, 20, 20)];
label.backgroundColor = [UIColor blackColor];
[self.view addSubview:label];
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:2.0
target:self
selector:#selector(createRandomPoint:)
userInfo:nil
repeats:YES];
screenHeight = [UIScreen mainScreen].bounds.size.height;
screenWidth = [UIScreen mainScreen].bounds.size.width;
}
-(void) createRandomPoint:(id)sender {
int randX = arc4random() % screenWidth;
int randY = arc4random() % screenHeight;
label.center = CGPointMake(randX, randY);
}