UIView creation and positioning - objective-c

Question

I have in my controller two UIView members, progressLineView and buttonsView. At some point I call this method:
- (void) drawPlayProgressLine{
progressLineView = [[UIView alloc] initWithFrame:CGRectMake(0.0, 0.0, 1, buttonsView.frame.size.height)];
progressLineView.backgroundColor = [UIColor whiteColor];
[buttonsView addSubview:progressLineView];
}
Everything works fine, and I also have a method that changes the position of the view:
- (void) moveProgressLine{
CGRect frame = progressLineView.frame;
frame.origin.x++;
progressLineView.frame = frame;
}
After the moveProgressLine method is called a few times and I want to call drawPlayProgressLine again, instead of completely moving the view to the starting position, it creates a new view. The more drawPlayProgressLine is called, the more views I get on my screen but I only need one.
I don't understand how this can happen when I'm creating only one object. How can I move the view instead of having a new one created each time? And another question: how can completely remove it (until the drawPlayProgressLine method is called to create it again)

Answer 1

I don't understand how this can happen when I'm creating only one object.
You create a new view every time you call your -drawPlayProgressLine method. Call it 10 times, you get 10 views.
How can I move the view instead of having a new one created each time?
Don't create the view each time through -drawPlayProgressLine. Instead, you can do either of:
Create progressLineView once, when the view controller's view hierarchy is created. -viewDidLoad is a perfect place for that sort of thing.
Check the value of progressLineView and create it only if it is currently nil.
Whichever you choose, assuming progressLineView is an instance variable, you can do exactly what you're doing in your -moveProgressLine method. That is, just use progressLineView as though it already exists, because it does. BTW, an easy way to move a view is to modify it's center property:
CGPoint *c = progressLineView.center;
c.x += 25.0;
progressLineView.center = c;
And another question: how can completely remove it (until the
drawPlayProgressLine method is called to create it again)
One approach is to simply hide the view when you're not using it. Another is to remove it from its super view (and release it if you've retained it), and then set your progressLineView to nil. So, if progressLineView is an ivar, do this:
[progressLineView removeFromSuperview];
[progressLineView release]; // if you're not using ARC and have retained it
progressLineView = nil;

Answer 2

you should just check if its created yet before creating it and move it if necessary:
- (void) drawPlayProgressLine{
if(progressLineView == nil)
{
progressLineView = [[UIView alloc] init];
progressLineView.backgroundColor = [UIColor whiteColor];
[buttonsView addSubview:progressLineView];
}
progressLineView.frame = CGRectMake(0.0, 0.0, 1, buttonsView.frame.size.height);
}

Answer 3

You are probably not invalidating the parent view. New objects are not created, but rather their presentation is left on the screen after you move them.
As for the second question:
[progressLineView removeFromSuperview];
[progressLineView release];
progressLineView = nil;