How to reuse a UILabel? (Or any object) - iphone

Question

This:
UILable *myLabel = [[UILabel alloc] init];
UILable *myLabel = [[UILabel alloc] init];
gives me a redefinition error.
But this:
for(i=0;i<5;i++)
{
UILable *myLabel = [[UILabel alloc] init];
// some label code here
[self.view addSubview:myLabel];
[myLabel release];
}
doesn't. So is the second one false? Should I define it before and just reuse it?
Is that right:
UIIMageView *Sign;
//Some Sign Stuff
Sign = [[UIImageView alloc]init];
Sign.image = [UIImage imageNamed:#"Minus.png"];
frame = CGRectMake(160 ,80, 64, 64);
Sign.frame = frame;
[scrollView addSubview:Sign];
Sign = nil;
[Sign release];
//Some other Sign stuff
Sign = [[UIImageView alloc]init];
Sign.image = [UIImage imageNamed:#"Plus.png"];
frame = CGRectMake(200 ,80, 64, 64);
Sign.frame = frame;
[scrollView addSubview:Sign];
Sign = nil;
[Sign release];
is that correct? That doesnt work without the Sign = nil. So it seems a little wobbly too.

Answer 1

You cannot have identical variable names used in the same block level scope. So in your first example you cannot have a variable definition with the same name, you have to name them differently.
- (void) method {
UIImageView* image1;
// here we define a new block scope. This can be a block of any kind (while, for, if)
{
// All reference in this block to this variable will see this definition.
UIImageView* image1;
// Using image1 here
}
// Here we see again the image1 defined at the beginning of the method.
}
In your loop example you are in a new scope that it's reinitialize after each iteration.
Your third example is correct in that it define the variable only one time. You reuse this variable after that to assign a new object. The third one is less elegant in that your variable name does not describe well for each case what are their purpose.
For your case of 'Sign = nil' this effectively make the line that follows useless since in Objective-C a message sent to a nil object is ignored.
I would suggest to define a method that you can call to create your images that look the same. Something like:
- (void) createImage:(NSString*) image frame:(CGRect) frame {
UIImageView *Sign;
Sign = [[UIImageView alloc]init];
Sign.image = [UIImage imageNamed:image];
Sign.frame = frame;
[self.scrollView addSubview:Sign];
[Sign release];
}

Answer 2

Your for-loop is perfectly fine. The scope of myLabel is limited to one run of your for-loop. So each run a new variable to hold the reference to your UILabel is created.
The second code you posted has leaks.
Sign = nil
[Sign release]
This will release the object at address nil and not the object you created. I can't see what else is wrong with your code, but your fix is definitely not fixing the root cause. Maybe it will help to post what error/warning you get when removing Sign = nil.
Also note that starting your variable names with a capital letter is not a good naming convention, because usually class names start with one.