Memory management, should I be retaining? - objective-c

Question

If I declare an NSString in my header file as follows:
{
NSString *testString;
}
#property(nonatomic,retain) NSString *testString;
Then synthesize the string in my .m file, what is the correct way to initialise it?
If I don't write:
self.testString = [[NSString alloc] init];
then the it is never initialised, but if I do, then isn't the string being retained twice? Or should I initialise it some other way, such as:
self.testString = [NSString stringWithFormat:#"%#, sampleText];

Answer 1

You are correct, the former will over retain the object.
Use the second form instead.
If you had to use the ivar directly however, you need to retain the object :
testString = [[NSString stringWithFormat:#"%#, sampleText] retain];

Answer 2

self.testString = [NSString stringWithFormat:#"%#, sampleText]; or self.testString = [NSString string]; is correct; self.testString = [[NSString alloc] init]; will cause over-retaining.
Consider using ARC (Automatic Retain Counting) for you project. With ARC the compiler takes care of retain counts so you don't have to, in fact aren't allowed to. There is a refactoring that will convert a current project.

Answer 3

It seems that you declare an variable called testString in your .h and you also create a property that retains.
You can either use this:
self.testString = [NSString string];
or you can use
testString = [[NSString alloc] init];
Defining the variable through the property will cause it to be retained, that's why you declared it as (nonatomic, retain). Defining the variable through the declaration won't take those arguments into consideration. Here's a quick rule of thumb about retaining.
Using your code as a base:
self.testString = [[NSString alloc] init]; // Retain count = 2
self.testString = [NSString string]; // Retain count = 1
testString = [[NSString alloc] init]; // Retain count = 1
testString = [NSString string]; // Not retained at all.

Answer 4

First of all #property (nonatomic, copy) NSString *testString to avoid mutability bugs.
Second - if you want just a string without leaks:
self.testString = [NSString string];
self.testString = [[[NSString alloc] init] autorelease];
self.testString = [NSString stringWithFormat:#"%#", text];
these are all valid options.